Engineering a layered-differentiation core–shell architecture: NiCoAlO_x@Pt/ZSM-5 for synergistically enhanced activity and dual H₂O/SO₂ resistance in propane oxidation

Abstract

Pt-based catalysts, though efficient for alkane C–H activation, suffer from water and SO₂ poisoning due to competitive adsorption on Pt sites. Herein, a core–shell Ni₁Co_0.5AlO_x@Pt/ZSM-5 catalyst was constructed via supramolecular assembly to improve the anti-poisoning performance, featuring a layered differentiation function. The ZSM-5 shell selectively sequesters H₂O and SO₂, preventing their access to Pt sites, while promoting the formation of active species such as Pt⁰, Co³⁺, and adsorbed oxygen. The optimized catalyst exhibits enhanced activity, water resistance, and sulfur tolerance in propane combustion. In situ DRIFTS confirmed the oxidation pathway as follows: propane is first activated at Pt⁰ sites to form isopropyl species, subsequently oxidized via Co³⁺-mediated sites to intermediates such as propene and acetate salts, and finally fully converted into CO₂ and H₂O with the participation of adsorbed oxygen. DFT calculations elucidated that this catalyst achieves superior propane oxidation activity and dual H₂O/SO₂ resistance via strengthened propane adsorption, reduced reaction energy barriers, and selective trapping of H₂O/SO₂ by the ZSM-5 shell. This atomic-level insight verifies that H₂O and SO₂ are preferentially sequestered by the ZSM-5 shell (rather than occupying Pt active sites), thus ensuring efficient propane/O₂ diffusion to Pt surfaces. This work provides a rational design strategy for robust, poisoning-resistant VOC oxidation catalysts.

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Broader context

Volatile organic compounds (VOCs), typified by propane, are key precursors of photochemical smog and tropospheric ozone, threatening the atmospheric environment and public health. Catalytic oxidation is the most effective industrial abatement route, yet state-of-the-art Co-based catalysts suffer severe deactivation under realistic flue gas conditions. The coexistence of H₂O and SO₂ causes competitive adsorption, active-site sulfidation, and irreversible degradation, restricting practical applications. Herein, we construct a layered-differentiated Ni₁Co_0.5AlO_x@Pt/ZSM-5 core–shell catalyst via supramolecular assembly and hydrothermal encapsulation. The Pt/ZSM-5 shell acts as a selective barrier to sequester H₂O and SO₂, while the LDH-derived core provides sufficient redox sites for propane activation. The optimized catalyst exhibits outstanding low-temperature activity, H₂O tolerance, and SO₂ durability. The core–shell interface optimizes electron transfer and stabilizes active species, reducing the C–H activation barrier. This work provides an atomic-level design principle for robust anti-poisoning catalysts toward efficient VOC elimination in harsh industrial exhausts.

1. Introduction

Volatile organic compounds (VOCs), primarily emitted from petrochemical, printing and dyeing, and manufacturing industries, are typically highly toxic, carcinogenic, and photochemically active, posing significant risks to both human health and the atmospheric environment.^1,2 Among various abatement strategies, catalytic combustion has emerged as one of the most effective technologies due to its high destruction efficiency, low ignition temperature, and minimal secondary pollution.^3–5 Propane (C₃H₈), a model VOC, exhibits low reactivity at mild temperatures due to its strong C–H bonds. Accordingly, Pt-based catalysts are considered highly effective, owing to their superior C–H bond activation and oxygen adsorption/activation capabilities.^6,7 For Pt-based catalysts, the support exerts a critical influence on performance by regulating the dispersion and electronic structure of Pt species. Water vapor in industrial VOC streams can deactivate catalysts through competitive adsorption or alteration of their physicochemical properties; hydrophobic supports effectively suppress water adsorption and enhance moisture tolerance.^8,9 Consequently, substantial research efforts have been devoted to the rational design of high-performance and durable catalysts capable of maintaining activity under complex and variable operating conditions.

Layered double hydroxides (LDHs), a class of anionic clays, have attracted considerable attention in heterogeneous catalysis due to their tunable composition and structure. Their general formula is [M_1−x²⁺M_x³⁺(OH)₂]^x+(Aⁿ⁻)_x/n(mH₂O), where M²⁺ and M³⁺ represent divalent and trivalent metal cations (e.g., Ni²⁺, Co²⁺, Al³⁺, and Ce³⁺), and Aⁿ⁻ and H₂O denote interlayer anions and water molecules, respectively.¹⁰ Upon high-temperature calcination, LDHs are converted into mixed metal oxides (MMOs) with mesoporous structures formed by stacked nanosheets, facilitating efficient reactant-active site interactions and product diffusion.^6,11,12 The presence of Al³⁺ promotes nanosheet growth, enhances crystallinity, and provides a robust framework for anchoring Ni and Co, thereby facilitating redox activity.¹¹ Furthermore, intercalation of anionic metal complexes such as PtCl₆²⁻ into LDH interlayers enables the formation of atomically dispersed active sites upon calcination, driven by the two-dimensional (2D) confinement effect, thus enhancing catalytic stability.¹³ For instance, Meng et al. synthesized a Ru₁Co_n single-atom alloy (SAA) catalyst by exploiting electrostatic repulsion between RuCl₅²⁻ and interlayer anions, preventing agglomeration and enabling uniform dispersion during thermal treatment.¹⁴ Similarly, Zhang et al. employed this strategy to prepare a highly active and stable Ru single-atom catalyst.¹⁵ However, despite their excellent catalytic performance, LDH-derived oxides generally exhibit poor water resistance, likely due to the intrinsic hydrophilicity caused by Al species in the LDH precursor, highlighting the need to improve moisture tolerance.^6,11,16

Water vapor can significantly inhibit catalytic oxidation of VOCs by competitively occupying active sites or altering their physicochemical properties, and this detrimental effect can be alleviated by employing hydrophobic coatings or supports, which reduce H₂O adsorption and minimize performance loss.⁹ Coating the catalyst with appropriate shell materials not only protects the active metal from deactivation but also enables synergistic effects at the core–shell interface, thereby enhancing catalytic activity.¹⁷ ZSM-5, a silica–alumina zeolite with the general formula M_2/nO·Al₂O₃·ySiO₂·zH₂O (where n is the valence of the charge-compensating cation and y represents the SiO₂/Al₂O₃ ratio), features a unique ten-membered ring structure composed of interconnected SiO₄ or AlO₄ tetrahedra.¹⁸ Its hydrophobicity is primarily governed by the SiO₂/Al₂O₃ ratio and the concentration of surface silanol groups.^19–22 Wang et al. showed that a higher SiO₂/Al₂O₃ ratio and lower Si-OH content in ZSM-5 confer greater hydrophobicity, which in turn enhances the water resistance of Pt/ZSM-5 catalysts.²⁰ Furthermore, researchers have conducted extensive studies on the sulfur resistance of catalytic oxidation systems for VOCs, with key strategies including hydrophobic zeolite coating, surface acidity regulation, core–shell spatial confinement, and modulation of metal electronic structures.²² However, existing catalysts still generally suffer from difficulties in simultaneously resisting combined H₂O and SO₂ poisoning, the challenge of balancing activity and stability under complex atmospheres, and a lack of clarity regarding atomic-level anti-poisoning mechanisms. Very few studies have integrated the four key functions: propane activation, oxygen migration, resistance to H₂O poisoning, and resistance to SO₂ poisoning, into a single catalyst through the design of a layered core–shell structure.

To mitigate catalyst deactivation under H₂O/SO₂ exposure, a Ni₁Co_0.5AlO_x catalyst derived from LDHs was synthesized via a supramolecular assembly strategy and hydrothermally coated with a Pt/ZSM-5 shell. Systematic modulation of Pt location (within the Ni₁Co_0.5AlO_x core or the ZSM-5 shell) and shell thickness enabled performance optimization. The Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalyst with Pt deposited on the 3 wt% shell exhibits the optimal balance between H₂O and SO₂ resistance. The possible propane oxidation pathways under both air and SO₂-containing atmospheres were investigated by in situ DRIFTS. This strategy offers a promising route to designing durable, high-performance Pt-based catalysts for propane oxidation under severe conditions.

2. Experimental

2.1. Synthesis of Pt/Ni_aCo_bAlO_x catalysts

Pt/Ni_aCo_bAlO_x catalysts were synthesized via a supramolecular assembly method, wherein NiAl-(PtCl₆²⁻)-LDH precursors were first prepared and subsequently calcined.^6,15 The theoretical Pt loading and the molar ratio of (a + b)/c were fixed at 0.5 wt% and 3 : 1, respectively, while the Ni : Co molar ratio (a : b) was varied: 1 : 0, 1 : 0.5, 0.5 : 1, and 0 : 1. The synthesis procedures for other Pt/Ni_aCo_bAlO_x catalysts were the same as that of Pt/NiAlO_x, with variations only in the amounts of Ni(NO₃)₂·6H₂O, Co(NO₃)₂·6H₂O and H₂PtCl₄.

2.2. Synthesis of the Pt/Ni₁Co_0.5AlO_x@ZSM-5(5%) catalyst

To systematically investigate the influence of Pt position on catalyst performance, we also prepared the Pt/Ni₁Co_0.5AlO_x@ZSM-5(5%) catalyst. The Pt/Ni₁Co_0.5AlO_x core was synthesized via the preparation of a Ni₁Co_0.5Al-(PtCl₆²⁻)-LDH precursor, following the same synthesis route as that of the Pt/Ni₁Co_0.5AlO_x catalyst. The resulting mixture was subjected to hydrothermal treatment at 180 °C for 48 h. Finally, the dried solid was ground into a uniform powder and calcined at 550 °C for 4 h (heating rate: 1 °C min⁻¹) to yield the Pt/Ni₁Co_0.5AlO_x@ZSM-5(5%) catalyst containing 0.5 wt% Pt.

2.3. Synthesis of Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%), Ni₁Co_0.5AlO_x@Pt/ZSM-5(5%) and Ni₁Co_0.5AlO_x@Pt/ZSM-5(10%) catalysts

To systematically investigate the influence of shell content on the catalytic performance, core–shell catalysts with different shell thicknesses were also fabricated. The synthesis of Pt/ZSM-5 shells with varying mass fractions (3%, 5%, and 10%) followed the same procedure as the standard ZSM-5 shell synthesis, with modifications in the amounts of water glass and n-butylamine and replacement of the Pt/Ni₁Co_0.5AlO_x core with the corresponding amounts of the Ni₁Co_0.5AlO_x core. The detailed preparation procedure for catalysts with different Pt/ZSM-5 shell mass fractions is provided in the supplementary information (SI). The synthesis procedures of Ni₁Co_0.5AlO_x@Pt/ZSM-5 catalysts are illustrated in Fig. 1a.

Fig. 1 (a) Schematic illustration of the synthesis process for Ni₁Co_0.5AlO_x and Ni₁Co_0.5AlO_x@Pt/ZSM-5 catalysts. TEM and HRTEM images and plane of Pt/Ni₁Co_0.5AlO_x (b) and Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) (c) catalysts. TEM images and mapping analysis of Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalyst (d).

2.4. Catalyst characterization studies

Characterization techniques employed in this study included TEM, EDS mapping, XRD, Raman spectroscopy, FTIR, O₂/SO₂/H₂O/NH₃-TPD, H₂-TPR, BET surface area analysis, XPS, in situ DRIFTS and DFT calculations. Detailed experimental procedures are provided in the SI.

2.5. Theoretical calculations

Density functional theory (DFT) calculations were performed using the Vienna ab initio simulation package (VASP). Details concerning the definitions and computational procedures are provided in the SI.

3. Results and discussion

3.1. Morphology and microstructure

We observed the morphology of Pt/Ni₁Co_0.5AlO_x and the core–shell catalysts via TEM electron microscopy, and the results are shown in Fig. 1 and Fig. S1 and S2. The five catalysts retained well-defined nanosheet structures derived from the layered double hydroxide (LDH) precursors, confirming the successful synthesis of hydrotalcite-derived oxides. Compared with the Pt/Ni₁Co_0.5AlO_x catalyst, the Ni₁Co_0.5AlO_x@Pt/ZSM-5 catalysts exhibited numerous disordered fibrous bundles of varying sizes distributed across the nanosheet surfaces (Fig. S1c–j). These straight, fiber-like structures contributed to the increased thickness of the nanosheets. Notably, the morphology and structure of the Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%), Ni₁Co_0.5AlO_x@Pt/ZSM-5(5%), and Ni₁Co_0.5AlO_x@Pt/ZSM-5(10%) catalysts reveal that the thickness of the coating layer progressively increases with increasing Pt/ZSM-5 shell content (Fig. S1e, g and i). This indicates that ZSM-5 or Pt/ZSM-5 layers have successfully grown upon the surface of the LDH-derived oxides. The morphology and lattice spacing of the Pt/Ni₁Co_0.5AlO_x catalyst are shown in Fig. 1b. The average particle size of Pt/Ni₁Co_0.5AlO_x is approximately 33.18 nm, with a lattice spacing of 0.31 nm corresponding to the (220) plane of Co₃O₄. Fig. 1c displays the morphology and lattice spacing of the Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) sample. The average particle size of Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) is approximately 39.26 nm, slightly larger than that of Pt/Ni₁Co_0.5AlO_x, which indirectly confirms the successful encapsulation of the Pt/ZSM-5 shell. Elemental mapping of the Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalyst, shown in Fig. 1d, reveals that Ni, Co, O, and Pt were homogeneously distributed within the nanosheet matrix, indicating uniform dispersion of active components, which is beneficial for propane oxidation. The uniform distribution of Al provided abundant core sites for ZSM-5 or Pt/ZSM-5 shell growth, while the homogeneous dispersion of Si confirmed uniform coverage of the molecular sieve shells on the LDH-derived oxides.

3.2. Catalytic performance

Considering that the distribution of the active component Pt is a key factor influencing propane oxidation performance, we conducted a series of comparative performance tests on three catalysts: Pt/Ni₁Co_0.5AlO_x, Pt/Ni₁Co_0.5AlO_x@ZSM-5(5%), and Ni₁Co_0.5AlO_x@Pt/ZSM-5(5%). The results are presented in Fig. 2 and Fig. S3. Fig. 2 shows the systematic investigation of the influence of Pt distribution and ZSM-5 shell formation on the propane oxidation performance of Pt/Ni₁Co_0.5AlO_x-based catalysts. Under dry conditions, the Pt/Ni₁Co_0.5AlO_x catalyst exhibits outstanding low-temperature catalytic activity, indicating that the active components are fully exposed and effectively promote propane oxidation (Fig. 2a). Upon introduction of 5 vol% H₂O, activity declined across all catalysts, with Ni₁Co_0.5AlO_x@Pt/ZSM-5(5%) exhibiting the smallest decrease, confirming the Pt/ZSM-5 shell structure's tolerance to water molecules (Fig. 2b). The Pt/Ni₁Co_0.5AlO_x@ZSM-5(5%) catalyst showed significantly improved water resistance (ΔT₉₀ = −20 °C), although the encapsulated Pt was less accessible to propane, likely due to the overly thick ZSM-5 shell, resulting in a lower activity. Conversely, Ni₁Co_0.5AlO_x@Pt/ZSM-5(5%) retained high catalytic performance, demonstrating that water molecules did not significantly poison its active centers. This result confirms that confining Pt within the ZSM-5 shell constitutes an effective strategy. It maintains catalytic activity while suppressing water molecule occupation of active sites, thereby mitigating activity decline. Fig. 2c and d display the calculation of the apparent activation energies (E_a) for the three catalysts under dry and humid conditions. The E_a trends correlate closely with catalytic activity. Under water-permeable conditions, Pt/Ni₁Co_0.5AlO_x exhibits a marked increase in E_a, indicating water molecules inhibit its low-temperature oxidation efficiency. Whereas Ni₁Co_0.5AlO_x@Pt/ZSM-5(5%) shows no discernible E_a shift, demonstrating that the ZSM-5 shell not only shields Pt active sites but also optimizes reactant diffusion and adsorption behavior, synergistically lowering the reaction energy barrier. Furthermore, we conducted water resistance stability tests on all three samples at T₉₀ (temperatures corresponding to 90% propane conversion) under dry air conditions (Fig. 2e). After 20 h of reaction in a 5 vol% H₂O atmosphere, the propane conversion rate of Ni₁Co_0.5AlO_x@Pt/ZSM-5(5%) remained at 85.9%, substantially higher than the 55.9% observed for Pt/Ni₁Co_0.5AlO_x without the shell. Similarly, the anti-SO₂ performance test results are shown in Fig. 2f. Under a 20 ppm SO₂ atmosphere, the Pt/Ni₁Co_0.5AlO_x catalyst without the ZSM-5 shell exhibited a sharp decline in stability, ultimately achieving a conversion rate of only 42.2%. However, the Ni₁Co_0.5AlO_x@Pt/ZSM-5(5%) sample exhibited a gradual decrease in the conversion rate. These findings demonstrate that the ZSM-5 shell physically shields active sites from contact with toxic molecules, preventing direct poisoning and significantly enhancing catalyst stability under complex atmospheres.

Fig. 2 Catalytic activity of Pt/Ni₁Co_0.5AlO_x and its core–shell catalysts under dry air and 5 vol% H₂O conditions (a) and (b). E_a of Pt/Ni₁Co_0.5AlO_x and its core–shell catalysts under dry air (c) and 5 vol% H₂O (d) conditions. Anti-H₂O ability (e) and anti-SO₂ ability (f) of Pt/Ni₁Co_0.5AlO_x and its core–shell catalyst.

Based on the above performance analysis, we found that the percentage content of the Pt/ZSM-5 shell layer is crucial for enhancing the catalyst's resistance to poisoning and stability. Therefore, we further prepared catalysts with varying Pt/ZSM-5 shell contents. Fig. 3 displays the systematic investigation of the influence of the Pt/ZSM-5 shell content (3%, 5%, 10%) on the propane oxidation activity, kinetics, and poisoning resistance stability of the Ni₁Co_0.5AlO_x@Pt/ZSM-5 catalyst, identifying the optimal threshold effect of shell content. The results are illustrated in Fig. 3a–h and Fig. S4–S10 and Table 1. Under dry air conditions, the propane oxidation activity followed the order: Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) > Ni₁Co_0.5AlO_x@Pt/ZSM-5(5%) > Ni₁Co_0.5AlO_x@Pt/ZSM-5(10%) (Fig. 3a). Compared to other core–shell catalysts, the enhanced activity of Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) probably arises from highly accessible Pt sites on the outer shell and a thin ZSM-5 layer that promotes efficient reactant diffusion. The introduction of 5% H₂O resulted in a slight decrease in activity for all catalysts. However, the 3% shell sample still exhibited the lowest T₉₀ among the three, indicating that a lower shell layer content is more conducive to the diffusion and adsorption of reactants near the active sites (Fig. 3b). The Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalyst exhibits higher activity than the bare Pt/Ni₁Co_0.5AlO_x catalyst under both dry air and 5 vol% H₂O conditions, indicating that the 3 wt% Pt/ZSM-5 shell enhances the redox performance and water tolerance of the Ni₁Co_0.5AlO_x core through interfacial interactions (Fig. S5).

Fig. 3 Catalytic activity of core–shell structured Ni₁Co_0.5AlO_x@Pt/ZSM-5 catalyst under dry air and 5 vol% H₂O conditions (a) and (b). Anti-H₂O ability (c). E_a of core–shell structured Ni₁Co_0.5AlO_x@Pt/ZSM-5 catalyst under dry air (d) and 5 vol% H₂O (e) conditions. Comparison of R_s and R_m with respect to temperature variation (f). Anti-SO₂ ability (g) and CO₂ selectivity (h) of Pt/Ni₁Co_0.5AlO_x and its core–shell catalysts. Comparison of catalytic properties for propane oxidation of Pt-based catalysts reported in the literature with this work (i).

Table 1 Catalytic properties of Pt/Ni₁Co_0.5AlO_x and its core–shell catalysts for propane oxidation

Catalysts	Dry			Wet			Difference
	T50^a (°C)	T90^a (°C)	Ea^b (kJ mol^−1)	T50^a (°C)	T90^a (°C)	Ea^b (kJ mol^−1)	ΔT90^c (°C)	ΔEa^c (kJ mol^−1)
a The reaction temperatures at 50% and 90% propane conversion under dry air and 5 vol% H2O conditions.b Ea values were obtained by calculating the slope of the Arrhenius curve for propane conversion under 20%.c Difference between Ea and T90 of the same catalyst under dry air and 5 vol% H2O conditions.
Pt/Ni1Co0.5AlOx	317	374	41.6	376	450	51.0	76	9.4
Pt/Ni1Co0.5AlOx@ZSM-5(5%)	353	440	49.4	354	420	48.4	−20	−1.0
Ni1Co0.5AlOx@Pt/ZSM-5(3%)	293	368	39.7	332	393	44.3	25	4.6
Ni1Co0.5AlOx@Pt/ZSM-5(5%)	323	400	44.8	313	410	46.0	10	1.2
Ni1Co0.5AlOx@Pt/ZSM-5(10%)	336	450	50.6	340	455	53.0	5	2.4

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To evaluate the practical applicability of these catalysts under realistic conditions, H₂O was introduced into the reaction feed to simulate typical industrial exhaust environments. As shown in Fig. 3c, under 5 vol% H₂O conditions, the propane conversions of the three catalysts remained stable during the initial 3 h but subsequently declined by 16.2% (Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%)), 4.57% (Ni₁Co_0.5AlO_x@Pt/ZSM-5(5%)) and 18.4% (Ni₁Co_0.5AlO_x@Pt/ZSM-5(10%)) over the next 12 h, respectively. This activity loss is likely due to competitive adsorption of H₂O molecules with propane, O₂, and reactive intermediates on active sites, which weakens reactant adsorption and inhibits the formation of reactive species. Consequently, the interaction between reactants and active centers is suppressed, leading to reduced catalytic activity. Furthermore, H₂O may irreversibly deactivate moisture-sensitive active sites through direct interaction, resulting in permanent loss of activity. Compared to the Pt/Ni₁Co_0.5AlO_x catalyst, the four core–shell catalysts exhibited reduced activity loss, indicating that the ZSM-5 shell effectively suppressed H₂O adsorption and inhibited direct interaction between H₂O and active sites. An increased H₂O resistance of the four core–shell catalysts may stem from the relatively high Si/Al ratio of ZSM-5, which reduces the density of polar Si–O–Al linkages while increasing nonpolar Si–O–Si bonds, thereby weakening the interaction between polar H₂O molecules and active sites and decreasing hydrophilicity.¹⁹ Additionally, the optimal anti-H₂O stability of the Ni₁Co_0.5AlO_x@Pt/ZSM-5(5%) catalyst may arise from its moderately thick hydrophobic Pt/ZSM-5 shell, which potentially inhibits H₂O adsorption and shields Pt from water-sensitive sites in the LDH-derived Ni₁Co_0.5AlO_x core. To determine E_a under dry air and 5 vol% H₂O conditions, four data points with propane conversion below 20% were selected from the activity curves shown in Fig. 3a and b. The corresponding E_a are summarized in Fig. 3d and e and Table 1. Generally, a lower E_a indicates that VOC molecules are more readily activated on the catalyst surface, reflecting higher intrinsic activity. Under dry conditions, E_a followed the trend: Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) < Ni₁Co_0.5AlO_x@Pt/ZSM-5(5%) < Ni₁Co_0.5AlO_x@Pt/ZSM-5(10%), which is consistent with their activity ranking, confirming differences in ease of propane activation over different catalyst surfaces. As shown in Fig. S6, E_a, reaction rate (r) and T₉₀ of the same catalyst exhibit strong linear correlations, with E_a and r showing inverse trends relative to T₉₀, indicating that lower activation energy and higher reaction rates correspond to enhanced catalytic activity.

Catalytic stability tests of Pt/Ni₁Co_0.5AlO_x and its core–shell catalysts were performed at constant temperatures corresponding to high propane conversions (85.0–95.0%), with SO₂ introduced as needed. The SO₂ tolerance of the catalysts was also evaluated, as shown in Fig. 3f. After 12 h exposure to SO₂, propane conversion over the Pt/Ni₁Co_0.5AlO_x catalyst dropped sharply by 44.9% and did not recover after SO₂ removal, suggesting severe and irreversible SO₂ poisoning. In contrast, the decreases in propane conversion over Pt/Ni₁Co_0.5AlO_x@ZSM-5(5%), Ni₁Co_0.5AlO_x@Pt/ZSM-5(5%), and Ni₁Co_0.5AlO_x@Pt/ZSM-5(10%) catalysts were less distinct, while Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalyst even showed a 4.66% increase. The temporary increase in propane conversion on the Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalyst during SO₂ exposure may be attributed to the formation of sulfate/sulfite species with strong Lewis acidity, which promote propane adsorption and C–H bond activation.²³ These results demonstrate the excellent SO₂ tolerance of the Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalyst and highlight its strong potential for practical applications.²⁴ However, once SO₂ was removed, the five catalysts exhibited greater decreases in activity, likely due to the irreversible deactivation of active sites. As shown in Fig. S10, after 20 h of propane oxidation under dry conditions, the propane conversion over the Pt/Ni₁Co_0.5AlO_x catalyst declined by 8.20%, whereas the decrease over the four core–shell catalysts remained below 5.00%, indicating that the ZSM-5 and Pt/ZSM-5 shell effectively enhanced the thermal stability of the hydrotalcite-derived catalysts.

To further evaluate catalytic efficiency, the reaction rates normalized by specific surface area (R_s) and catalyst mass (R_m) were calculated at 140, 160, 180, 200, and 220 °C under both dry air and 5 vol% H₂O conditions, as shown in Fig. 3g and Fig. S7. The Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalyst exhibited the highest R_s and R_m at every temperature point, which were 4.3–7.6 and 2.6–6.2 times greater than those of other catalysts, respectively, indicating the highest catalytic efficiency. Furthermore, the Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalyst showed the smallest decrease in R_s and R_m under 5 vol% H₂O conditions, confirming its superior activity and water resistance. Turnover frequencies (TOF) based on the active metals under dry air and 5 vol% H₂O conditions were also calculated. Under dry conditions, the TOF_Pt at 220 °C confirms that the interactions between the 3 wt% Pt/ZSM-5 shell and the Ni₁Co_0.5AlO_x core enhance the intrinsic oxidation activity of the Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalyst. In contrast, all catalysts exhibited lower TOF_Pt, TOF_Ni and TOF_Co under 5 vol% H₂O conditions, highlighting the inhibitory effect of water vapor on the intrinsic reaction kinetics (Fig. S8). Fig. S9 shows the good linear correlations between TOF_Pt and T₉₀ of the catalyst under both dry air and 5 vol% H₂O conditions, suggesting that intrinsic catalytic activity directly governs light-off performance.

As shown in Fig. 3h, the CO₂ selectivity trend highly correlates with the propane conversion rate trend, confirming the high catalytic efficiency of Pt/Ni₁Co_0.5AlO_x and its core–shell catalysts. The Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalyst exhibits outstanding CO₂ selectivity, increasing rapidly in the ∼200 °C range and approaching 100% in the medium-to-high temperature range (>300 °C), consistently remaining significantly higher than other catalysts. The Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalyst not only efficiently activates propane at low temperatures but also drives the oxidation reaction to a deeper extent, significantly suppressing the formation of intermediate products. To provide an intuitive comparison of the propane catalytic combustion activity among different Pt-based catalysts, Fig. 3i and Table 2 present an analysis centered on T₅₀ and T₉₀ as core metrics. Notably, the T₅₀ and T₉₀ values of the Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalyst prepared in this work are significantly lower than those of conventional Pt-based catalysts, directly demonstrating its outstanding low-temperature activity advantage in propane catalytic combustion. Conventional Pt-based catalysts generally exhibit elevated T₅₀ and T₉₀ values due to weak interactions between the support and Pt, coupled with insufficient adsorption and activation capabilities for propane. The Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalyst overcomes this limitation through core–shell synergistic effects. ZSM-5 not only stabilizes Pt nanoparticles via strong interactions but also provides abundant oxygen vacancies and active oxygen species, thereby enhancing the low-temperature activation of propane C–H bonds.

Table 2 Comparison of catalytic properties for propane oxidation of Pt-based catalysts reported in the literature with this work

Catalysts	T50^a (°C)	T90^a (°C)	Pt content (wt%)	Concentration (ppm)	WHSV (mL g^−1 h^−1)	Ref.
a The reaction temperatures at 50% and 90% propane conversion under dry air conditions.
Pt/CeO2	318	380	0.8	0.2% C3H8 + 2% O2/Ar	150 000	7
1Pt/3.6Ce/Al2O3-RWH	360	450	1.0	0.1% C3H8 + 10% O2/Ar	40 000	67
Pt/Al2O3	472	591	—	0.2% C3H8 + 5% O2/Ar	30 000	68
Pt/Ti0.1AlOy	416	529	—	0.2% C3H8 + 5% O2/Ar	30 000	68
Pt/CeO2-SR	306	385	0.9	0.3% C3H8 + 20% O2/N2	30 000	69
Pt/CeO2-WI	334	389	1.0	0.3% C3H8 + 20% O2/N2	30 000	69
1%Pt/TiO2(bi-phasic)	355	400	1.0	0.5% C3H8 + 5% O2/He	50 000	70
Pt/Ni1Co0.5AlOx	317	374	0.5	0.2% C3H8 + 5% O2/Ar	30 000	This work
Pt/Ni1Co0.5AlOx@ZSM-5(5%)	353	440	0.5	0.2% C3H8 + 5% O2/Ar	30 000	This work
Ni1Co0.5AlOx@Pt/ZSM-5(3%)	293	368	0.5	0.2% C3H8 + 5% O2/Ar	30 000	This work

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3.3. Physicochemical properties of catalysts

The pore properties of Pt/Ni₁Co_0.5AlO_x and its core–shell catalysts are depicted in Fig. 4a and b. Both Pt/Ni₁Co_0.5AlO_x and Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalysts exhibited type IV isotherms based on the IUPAC classification, characteristic of mesoporous materials.²⁵ The Pt/Ni₁Co_0.5AlO_x catalyst displayed an H2 hysteresis loop, typically associated with ink-bottle-shaped pores, which likely originated from the partial collapse of the LDH structure during calcination at 400 °C.²⁶ In contrast, the Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalyst showed an H3 hysteresis loop, indicative of slit-shaped pores formed by the stacking of lamellar nanosheets. This suggests that the thin Pt/ZSM-5 coating preserved the mesostructural features of LDH-derived oxides.²⁷ In accordance with the literature, the unique micro-mesoporous composite structure may provide more optimal pathways for the adsorption and diffusion of propane.^28–30 As shown in Fig. 4b and Table S1, the five catalysts exhibited broad pore size distributions with abundant mesopores and relatively large specific surface areas, offering numerous contact sites for propane adsorption and oxidation. Compared with the Pt/Ni₁Co_0.5AlO_x catalyst, the four coated catalysts displayed slightly reduced mesopore volumes and surface areas, shown in Table S1, likely due to partial pore coverage by the ZSM-5 or Pt/ZSM-5 shell.

Fig. 4 Nitrogen adsorption–desorption isotherms (a), pore diameter distribution (b), and XRD (c) profiles of Pt/Ni₁Co_0.5AlO_x and its core–shell catalysts. (d) The electron location function and optimized mode of Pt/NiCoAlO_x and Ni₁Co_0.5AlO_x@Pt/ZSM-5. Raman (e) and FTIR (f) profiles of Pt/Ni₁Co_0.5AlO_x and its core–shell catalysts.

The crystalline phase structures of Pt/Ni₁Co_0.5AlO_x and its core–shell catalysts were examined by XRD technology, as depicted in Fig. 4c and Fig. S11. All five catalysts exhibited diffraction peaks at 19.1°, 31.4°, 37.0° and 45.0°, assigned to the (111), (220), (311), and (400) planes of NiAl₂O₄ (JCPDS 78-0052) and NiO (JCPDS 71-1179), as well as peaks at 19.0°, 31.3°, 36.8°, 44.8°, 59.4° and 65.2° attributed to (111), (220), (311), (400), (511) and (440) of Co₃O₄ (JCPDS 74-2120), respectively.^24,31 The absence of characteristic peaks for Al₂O₃ suggests that Al may be incorporated into NiAl₂O₄ spinel structures, existing as amorphous phases, or integrated into the ZSM-5 framework.³² The observed Ni-based and Co-based oxide peaks confirm the successful formation of mixed metal oxides derived from the hydrotalcite precursor. These peaks appeared slightly weakened in the four core–shell catalysts, likely due to the shielding effect of the ZSM-5 and Pt/ZSM-5 shells. No distinct diffraction peaks corresponding to ZSM-5 were detected, which may be attributed to the low crystallinity.³³ Similarly, the absence of Pt-related reflections indicates that Pt species may be highly dispersed in LDH derivatives and ZSM-5 due to the 2D space confinement effect of hydrotalcite or interaction between Pt and ZSM-5.^14,34

To gain deeper insight into the electronic interactions and structural evolution mechanisms induced by the core–shell structure, this study conducted localized electron function (ELF) calculations and structural optimization. The relevant results are shown in Fig. 4d (A1–A4). The ELF distribution maps (A1 for Pt/Ni₁Co_0.5AlO_x and A2 for Ni₁Co_0.5AlO_x@Pt/ZSM-5) visually represent the spatial distribution of electron localization, directly reflecting the chemical bonding nature and electron transfer characteristics at the interface. In A1 (Pt/Ni₁Co_0.5AlO_x), the electron localization around Pt atoms and Ni/Co sites exhibits a relatively uniform distribution, indicating the formation of metallic or ionic bonds within the LDH-derived oxides. Conversely, A2 (Ni₁Co_0.5AlO_x@Pt/ZSM-5) exhibits distinct electron localization patterns: the introduction of the ZSM-5 shell induces redistribution of electron density at the core–shell interface, enhancing electron localization around Si–O–Pt and Si–O–Co bonds. This interface-driven electronic rearrangement aligns with XPS findings, wherein the core–shell architecture modulates the oxidation states of Pt. Specifically, electron delocalization at the Pt/ZSM-5 interface promotes the formation of Pt⁴⁺ species, which exhibit reduced reactivity towards SO₂ and H₂O (verified by DFT adsorption energy calculations), thereby conferring exceptional anti-poisoning properties to the catalyst. Optimized structural models (A3: Pt/Ni₁Co_0.5AlO_x; A4: Ni₁Co_0.5AlO_x@Pt/ZSM-5) further elucidate the geometric and electronic effects of the core–shell design. In A3 (Pt/Ni₁Co_0.5AlO_x), Pt atoms are embedded within NiCoAlO_x, forming a relatively compact structure with limited exposure of Pt active sites. In contrast, the A4 model (Ni₁Co_0.5AlO_x@Pt/ZSM-5) shows Pt atoms anchored to the ZSM-5 surface, whose porous framework not only stabilizes Pt nanoparticles but also creates accessible pathways for propane/O₂ diffusion. Furthermore, the Si–O–Pt bonds in the A4 model induce tensile strain on the platinum atoms. Prior studies indicate that such a strain enhances C–H bond adsorption and activation. Collectively, these theoretical findings provide atomic-level evidence for core–shell synergy. The ZSM-5 shell modulates interfacial electron distribution through electronic free energy redistribution, while structural engineering optimizes the geometric environment of Pt active sites, thereby simultaneously enhancing catalytic activity and resistance to poisoning.

The phase structure evolution of Pt/Ni₁Co_0.5AlO_x and its core–shell catalysts was investigated via Raman spectroscopy, as shown in Fig. 4e. A prominent Raman band at 543 cm⁻¹, close to the characteristic peak of NiO (540 cm⁻¹), suggests the incorporation of Al³⁺ into the NiO lattice, forming Ni–O–Al bonds. This observation aligns with the absence of Al₂O₃-related peaks, supporting the inference that Al is integrated into the Ni-based oxide and ZSM-5 framework rather than existing as a separate phase.^6,24 The faint Raman peak at 588 cm⁻¹ of the five catalysts is attributed to the NiAl₂O₄ spinel phase, and the lack of additional spinel-related peaks is likely due to the structural disorder induced by the insertion of Al into NiO lattices, which disrupts the long-range order and diminishes peak visibility.³⁵ In the four coated catalysts, broad and weak bands observed in the 600–700 cm⁻¹ and 800–1000 cm⁻¹ regions correspond to the bending and stretching vibrations of T–O–T and T–O (T = Si, Al) bonds, respectively, indicating the presence of ZSM-5 or Pt/ZSM-5 framework.²⁹ The Si–O–Si bond in the ZSM-5 framework is a nonpolar species and shows weak affinity to polar water molecules, thus imparting good water resistance to the four coated catalysts in this work.¹⁹

The functional groups of Pt/Ni₁Co_0.5AlO_x and Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalysts were investigated via FTIR spectroscopy, as shown in Fig. 4f. Both catalysts exhibit characteristic bands at 3435 and 1630 cm⁻¹, corresponding to surface hydroxyl groups and physically adsorbed water (O–H and H–O–H vibrations), along with a band at 2922 cm⁻¹ attributed to C–H stretching and a peak at 1385 cm⁻¹ arising from C–O vibrations of carbonate species.^36,37 The broad band between 400 and 510 cm⁻¹ is associated with M–O (M = Ni, Co, and Al) lattice vibrations, confirming the formation of mixed metal oxides derived from hydrotalcite precursors.^37,38 The Si–O–Si bond in the framework imparts ZSM-5 hydrophobicity, thus improving the water resistance of the Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalyst.¹⁹ Furthermore, the markedly reduced intensity of O–H related bands (3435 and 1630 cm⁻¹) in the Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalyst suggests enhanced surface hydrophobicity imparted by the zeolite layer. These spectral features collectively confirm the core–shell structure and demonstrate that the Pt/ZSM-5 shell alters the surface environment, potentially contributing to improved hydrothermal resistance and catalytic performance.

XPS analysis was performed on Pt/Ni₁Co_0.5AlO_x and its core–shell catalysts, and the corresponding spectra are presented in Fig. 5a–e and Fig. S12 and S13. Due to the overlap between Pt 4f and Al 2p/Ni 3p signals, the Pt 4f spectra were fitted by fixing the Pt 4f_7/2 to Pt 4f_5/2 intensity ratio at 4 : 3 and maintaining a binding energy separation of 3.3 eV, as shown in Fig. 5a. Peaks at 67.60–67.86 eV and 69.60–69.86 eV were assigned to Ni 3p, while the signal at 74.00 eV corresponded to Al 2p.²⁷ In the Pt 4f region, the peaks at 71.40 and 74.70 eV were attributed to metallic Pt⁰, those at 72.50 and 75.80 eV to Pt²⁺, and those at 74.20 and 77.50 eV to Pt⁴⁺ species.⁷ The dominance of metallic Pt⁰ species on the five catalysts suggests the successful deposition of Pt nanoparticles on the Ni₁Co_0.5AlO_x core and ZSM-5 shell. Among these catalysts, Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) and Pt/Ni₁Co_0.5AlO_x exhibited the highest proportions of Pt⁰, which facilitates O₂ activation and C–H bond cleavage, thereby resulting in superior catalytic activity. However, the exposed Pt⁰ sites on the Pt/Ni₁Co_0.5AlO_x catalyst are susceptible to oxidation by SO₂ and competitive adsorption by H₂O, resulting in poor resistance to sulfur and moisture.^9,39 Conversely, the catalysts coated with ZSM-5 and Pt/ZSM-5 exhibited a higher Pt⁴⁺ content, illustrating that interactions between Pt and ZSM-5 promote the formation of high-valence Pt species, which is likely due to stabilization by the oxygen-rich environment and Al sites within the ZSM-5 shell.⁴⁰ Pt⁴⁺ offers superior chemical stability and lower reactivity toward SO₂ and H₂O, improving catalyst durability under harsh conditions.⁴¹ Moreover, the hydrophobic ZSM-5 shell acts as a physical barrier that suppresses SO₂ and H₂O access to Pt⁰ sites, thereby enhancing the poisoning resistance of the four core–shell catalysts. Additionally, this protective effect is more prominent with increased shell thickness or embedded Pt configurations. For instance, as shown in Fig. 3c, the Ni₁Co_0.5AlO_x@Pt/ZSM-5(5%) catalyst, featuring a 5 wt% ZSM-5 shell with embedded Pt, exhibits superior water resistance compared to both the Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalyst with a thinner (3 wt%) shell and the Pt/Ni₁Co_0.5AlO_x@ZSM-5(5%) catalyst, where Pt is confined into the Ni₁Co_0.5AlO_x core.

Fig. 5 XPS spectra of Pt 4f, Al 2p and Ni 3p (a), O 1 s (b), Ni 2p (c) and Co 2p (d) of Pt/Ni₁Co_0.5AlO_x and its core–shell catalysts. Ratios of Pt⁴⁺/Pt_total, O_latt/O_total, Si_framework/Si_total versus ΔT₉₀ (e) of Pt/Ni₁Co_0.5AlO_x and its core–shell catalysts. H₂ consumption (f), H₂-TPR profiles (g), NH₃-TPD (h) and O₂-TPD (i) profiles of Pt/Ni₁Co_0.5AlO_x and its core–shell catalysts.

As shown in Fig. 5b, the O 1s XPS spectra of Pt/Ni₁Co_0.5AlO_x and its core–shell catalysts exhibit three distinct peaks. The peak at 530.35–530.60 eV corresponds to lattice oxygen (O_latt), while those at 531.42–531.78 eV and 532.52–532.98 eV are attributed to adsorbed oxygen (O_ads) and surface hydroxyl groups (O_wat), respectively.⁴² Compared with the bare Pt/Ni₁Co_0.5AlO_x catalyst, the four coated catalysts exhibit positive shifts in the O_latt binding energy and increased proportions of O_latt (Fig. S12a). This enhancement is likely due to the oxidizing environment provided by Al and O species in the ZSM-5 shell, which strengthens M–O bonds and stabilizes high-valence metal cations, thereby promoting tolerance to SO₂ and H₂O.⁴⁰ The increase of O_latt content is particularly advantageous under humid and sulfur-rich conditions, where lattice oxygen plays a compensatory role when surface active oxygen is poisoned, thereby enhancing catalyst durability and poisoning resistance.⁴³ Furthermore, the four coated catalysts show positive shifts in the O_ads BE values compared to the bare Pt/Ni₁Co_0.5AlO_x catalyst, indicating that strong adsorption likely prevents rapid loss of active oxygen under SO₂- or H₂O-containing conditions. Meanwhile, after being coated with the ZSM-5 or Pt/ZSM-5 shell, the O_ads content in the catalysts decreases, except for Ni₁Co_0.5AlO_x@Pt/ZSM-5(5%) and Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%). As a more reactive and mobile species, O_ads is crucial for low-temperature oxidation and is often associated with oxygen vacancies.^6,44,45 The higher O_ads content in the Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalyst aligns with its superior activity, while the lower O_ads levels in other coated samples are consistent with reduced activity, highlighting the essential role of adsorbed oxygen in catalytic efficiency.

As shown in Fig. 5c, the Ni 2p XPS spectra of Pt/Ni₁Co_0.5AlO_x and its core–shell catalysts display two main peaks in the Ni 2p_3/2 region at 855.80 and 857.52 eV, corresponding to Ni²⁺ and Ni³⁺ species, respectively, along with a satellite feature near 862 eV. Similarly, in the Ni 2p_1/2 region, peaks at 873.80 and 875.52 eV were assigned to Ni²⁺ and Ni³⁺, with a satellite peak around 880 eV.^24,27 Compared with the bare Pt/Ni₁Co_0.5AlO_x catalyst, the four coated catalysts exhibit increased Ni³⁺/Ni²⁺ ratios, while the Ni 2p binding energies remain essentially unchanged. This indicates that ZSM-5 coating promotes Ni oxidation without altering its local coordination environment, indicative of surface reconstruction induced by the interactions between the Ni₁Co_0.5AlO_x core and the P/ZSM-5 shell. As shown in Fig. 5d, the deconvoluted Co 2p XPS spectra reveal Co³⁺ peaks at 780.70–780.98 eV and 795.70–795.98 eV, and Co²⁺ peaks at 782.77–783.15 eV and 797.77–798.15 eV.²⁴ As shown in Fig. 5d and Fig. S12b, compared to bare Pt/Ni₁Co_0.5AlO_x, the four coated catalysts exhibit positive shifts in Co³⁺ binding energies and a marked increase in Co³⁺ content, indicating that ZSM-5 favors the stabilization of high-valence cobalt species by interactions between the core and the shell. As Co³⁺ facilitates oxygen mobility and redox cycling, its highest proportion in the Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalyst correlates with the best low-temperature activity, highlighting the critical role of a high Co³⁺/Co²⁺ ratio in catalytic efficiency.²⁴ The XPS spectrum of Si 2p is shown in Fig. S13.

Fig. 5e and Fig. S14 reveal clear negative correlations between ΔT₉₀ and the contents of Pt⁴⁺, O_latt and Si_framework (framework Si species), with Si_framework in the Pt/Ni₁Co_0.5AlO_x@ZSM-5(5%) catalyst exhibiting an exceptionally strong inverse relationship. This demonstrates that Pt⁴⁺, O_latt and Si_framework enhance water tolerance by offering lower reactivity toward H₂O, compensatory oxygen species under humid conditions, and hydrophobicity to prevent competitive adsorption of H₂O, respectively. The core–shell catalyst contains higher concentrations of high-valence metal ions such as Co³⁺ and Pt⁴⁺ compared to the bare Pt/Ni₁Co_0.5AlO_x catalyst, confirming that the core–shell interactions promote the formation and stabilization of these oxidized species.

The reducibility of Pt/Ni₁Co_0.5AlO_x and its core–shell catalysts was investigated via H₂-TPR characterization, as presented in Fig. 5f, g and Fig. S15. Typically, Pt species reduce in the 60–120 °C range, but the corresponding signals were too weak to be resolved, likely due to the limited interaction between Pt and Ni₁Co_0.5AlO_x.^46,47 The bare Pt/Ni₁Co_0.5AlO_x catalyst exhibits a sharp peak at 300 °C and a strongly broad peak around 460 °C corresponding to the transition of NiO → Ni⁰ and Co₃O₄ → CoO → Co⁰, respectively, and a weakly broad peak at ∼750 °C corresponding to the overall reduction of the NiAl₂O₄ spinel phase.^47–53 This enhanced reducibility might partly account for the optimal activity of the Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalyst compared to the bare Pt/Ni₁Co_0.5AlO_x catalyst.

The acidity properties of Pt/Ni₁Co_0.5AlO_x and its core–shell catalysts were evaluated by NH₃-TPD, as exhibited in Fig. 5h and Fig. S16a. The profiles exhibit three distinct desorption regions corresponding to weak (50–300 °C), medium-strong (300–500 °C), and strong (500–800 °C) acid sites.⁴ Compared to the bare Pt/Ni₁Co_0.5AlO_x catalyst, the four core–shell catalysts show increased proportions of weak and medium-strong acid sites after coating with ZSM-5 and Pt/ZSM-5, enhancing propane adsorption and activation.^54–57 Specifically, the total percentage of weak and medium-strong acid sites follows the trend: Pt/Ni₁Co_0.5AlO_x (70.3%) < Ni₁Co_0.5AlO_x@Pt/ZSM-5(5%) (76.0%) < Ni₁Co_0.5AlO_x@Pt/ZSM-5(10%) (77.9%) < Pt/Ni₁Co_0.5AlO_x@ZSM-5(5%) (78.8%) < Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) (80.1%), with the highest value in the Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalyst correlating with its optimal catalytic activity. These acid sites include both Brønsted and Lewis types: Brønsted sites originate from surface hydroxyl groups (Ni–OH, Co–OH and Al–OH) in Ni₁Co_0.5AlO_x and bridging Si–OH–Al in the ZSM-5 framework, while Lewis sites arise from coordinatively unsaturated metal centers and extra-framework species. Their synergistic roles enhance propane adsorption, C–H bond cleavage, and oxidation efficiency, promoting propane consumption.^58,59 Moreover, Fig. S16a shows that the amount of acid sites on the four coated catalysts remains unchanged compared to the Pt/Ni₁Co_0.5AlO_x catalyst, which likely favors the dominance of metallic Pt⁰, partly accounting for the optimal activity of the Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalyst.⁶⁰

The oxygen species of Pt/Ni₁Co_0.5AlO_x and its core–shell catalysts were investigated by O₂-TPD, as depicted in Fig. 5i and Fig. S16b. The O₂-TPD profiles can be categorized into adsorbed oxygen (O_α) (50–300 °C), surface lattice oxygen (O_β) (300–600 °C), and bulk lattice oxygen (O_γ) (600–900 °C).⁵⁷ The relative content of O_α decreased in the order: Pt/Ni₁Co_0.5AlO_x@ZSM-5(5%) (20.7%) > Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) (17.1%) > Pt/Ni₁Co_0.5AlO_x (16.7%) > Ni₁Co_0.5AlO_x@Pt/ZSM-5(5%) (14.1%) > Ni₁Co_0.5AlO_x@Pt/ZSM-5(10%) (11.2%). This trend suggests that the movement of Pt species from the Ni₁Co_0.5AlO_x core to the ZSM-5 shell and increased shell thickness suppresses the formation of reactive adsorbed oxygen, leading to reduced low-temperature activity. As O_α and O_β are the primary active oxygen species, their depletion in Pt/Ni₁Co_0.5AlO_x@Z(5%), Ni₁Co_0.5AlO_x@Pt/ZSM-5(5%), and Ni₁Co_0.5AlO_x@Pt/ZSM-5(10%) catalysts may be responsible for the decline in catalytic activity.⁶¹ In contrast, coating with ZSM-5 and Pt/ZSM-5 significantly increased the amount of O_γ, likely due to enhanced bulk oxygen storage and release at elevated temperatures, which improved high-temperature oxygen cycling and contributed to better hydrothermal stability.⁴³ Additionally, Fig. S16b reveals that the four coated catalysts have less amount of oxygen species than the Pt/Ni₁Co_0.5AlO_x catalyst, indicating that the core–shell interactions modified oxygen species of hydrotalcite-derived oxides. Overall, ZSM-5-based shell coatings markedly altered the oxygen species distribution, thereby influencing catalytic activity and durability.

4. Exploration and discussion about the poisoning resistance mechanism of the ZSM-5 shell

To elucidate the reaction behaviors of propane over the Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalyst under both air and SO₂-containing atmospheres, in situ DRIFTS experiments were conducted to investigate its adsorption and oxidation behavior, as shown in Fig. 6 and Fig. S17. For the air atmosphere, the Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalyst was first pretreated in N₂ at 400 °C for 30 min and then cooled to 40 °C. A C₃H₈/Ar gas mixture containing 2000 ppm propane was subsequently introduced until surface saturation was reached. After purging with N₂ to remove weakly adsorbed species, the gas was switched to 20% O₂/N₂ mixture, and spectra were recorded during stepwise heating (100 °C, 150 °C, 200 °C, 250 °C, 300 °C, and 350 °C) to monitor surface species evolution. Fig. 6a and b present the in situ DRIFTS spectra of propane adsorption at 40 °C. After 6 min of propane exposure, characteristic asymmetric stretching bands of –CH₃ and –CH₂– groups appeared at 2970, 2892, and 2865 cm⁻¹, indicating initial propane adsorption.^4,7 By 8 min, these bands intensified, and new peaks emerged at 1474 cm⁻¹ (–CH₂– bending), 1373 cm⁻¹ (–CH₃ bending), and 1451 and 1541 cm⁻¹ (COO⁻ stretching), associated with carboxylate species.^7,62 These observations suggest that propane undergoes partial oxidation by surface oxygen species, even in the absence of gaseous O₂.^7,57 The continued increase in peak intensity until 26 min reflects progressive surface accumulation of propane, leading to saturation.

Fig. 6 in situ DRIFTS spectra of the Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalyst: Propane adsorption at 40 °C (a), propane oxidation in air (b)–(d) and propane oxidation in air/SO₂ (e)–(g). Schematic illustration of H₂O/SO₂-tolerant propane oxidation mechanism over the Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalyst (i).

Fig. 6b–d depict the stepwise oxidation of propane over the Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalyst under an air atmosphere. As the temperature increases, the characteristic C–H stretching bands of –CH₃ and –CH₂– groups (2800–3100 cm⁻¹) diminish and evolve into negative peaks at 100 °C, indicating the consumption of pre-adsorbed propane. Simultaneously, new weak bands emerge in the 1200–1800 cm⁻¹ region, corresponding to oxidation intermediates. Specifically, the peaks at 1640 cm⁻¹ (C=C), 1697 cm⁻¹ (C=O), and 1724 cm⁻¹ (C=O) are assigned to propylene, acetone, and propionaldehyde species, respectively.^4,7,62 Bands at 1610 cm⁻¹ and 1352 cm⁻¹ correspond to formate species (HCOO⁻), while those at 1582 cm⁻¹ and 1468 cm⁻¹ are attributed to acetate species (CH₃COO⁻).^57,63 These intermediates exhibit a temperature-dependent behavior: initially increasing in intensity and then diminishing, suggesting their transient formation and further oxidation. In parallel, bands at 1550 cm⁻¹ and 1530 cm⁻¹ are associated with carbonate species (CO₃²⁻), while the 1418 cm⁻¹ band corresponds to bicarbonate species (HCO₃⁻).^62,63 Their progressive growth with temperature indicates the occurrence of deep oxidation processes. At ∼200 °C, the characteristic bands of CO₂ and H₂O become apparent and continue to intensify. As shown in Fig. 6d, the acetone band (∼1700 cm⁻¹) increases at 150 °C and gradually decreases, turning into a negative band at 350 °C. The carboxylate (COO⁻) band at 1610 cm⁻¹ appears later, first intensifying and then disappearing at higher temperatures. The carbonate bands (1550 cm⁻¹ and 1530 cm⁻¹) correlate with the decline of carboxylates. These observations support a multi-step oxidation pathway: propane is initially dehydrogenated to form intermediates such as propylene, acetone, and propionaldehyde, which are further oxidized to carboxylates and carbonates, and eventually fully mineralized to CO₂ and H₂O.

For the SO₂-containing atmosphere study, the experimental procedure was identical to that under air, except that the reaction gas was replaced with air containing 30 ppm SO₂ after N₂ purging. Fig. 6e–g display the in situ DRIFTS spectra of propane oxidation over the Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalyst in air containing 30 ppm SO₂. At 40 °C, positive bands of propane (–CH₃ and –CH₂–) appear in the 2800–3100 cm⁻¹ region. These bands rapidly invert to negative at 100 °C and become more pronounced with increasing temperature, indicating progressive propane consumption. Compared to the reaction in pure air, shown in Fig. 6b, SO₂ presence leads to stronger initial adsorption bands, a sharper inversion, and greater negative intensity at the same temperatures, suggesting that SO₂ accelerates propane consumption, consistent with the previously observed slow increase in propane conversion upon SO₂ introduction. The band at 1271 cm⁻¹ corresponds to physically adsorbed SO₂, while the 1408 cm⁻¹ peak is attributed to SO₃, indicating that SO₂ not only adsorbs on the catalyst surface but also undergoes partial oxidation.⁴ This competitive adsorption of SO₂ may temporarily block active sites, while the formation of SO₃ may further interact with Pt species. Additionally, bands at 860 and 1317 cm⁻¹ are assigned to symmetric S–O–S vibrations and Pt-bound sulfite species, while peaks at 1346 and 1480 cm⁻¹ correspond to the asymmetric S=O stretching of surface sulfate species.^23,39 These results confirm that SO₂ reacts with Pt active sites to form sulfite and sulfate species, which are likely responsible for irreversible catalyst deactivation. Nevertheless, the evolution of reaction intermediates in the presence of SO₂, shown in Fig. 6g, remains similar to that under SO₂-free conditions, shown in Fig. 6d, suggesting that the overall oxidation pathway remains largely unaffected despite SO₂ interference.

Based on the analysis of the above characterization studies, the possible mechanism for the Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalyst's optimal activity and H₂O/SO₂ resistance in propane oxidation is shown in Fig. 6h. The high activity originates from the synergistic presence of metallic Pt⁰, Co³⁺, and O_ads and appropriately distributed weak and medium-strong acid sites. Together with the strong redox capacity of the composite, these features facilitate propane adsorption, C–H bond activation and subsequent complete oxidation. The excellent H₂O/SO₂ tolerance is attributed to the following two key factors. (1) The ZSM-5 shell physically hinders the diffusion of SO₂ and H₂O molecules over the active core. (2) The Si–O–Si framework of ZSM-5 exhibits intrinsic hydrophobicity, thereby weakening interactions with polar H₂O molecules. While these cations display lower reactivity toward H₂O and SO₂, the lattice oxygen enhances oxygen replenishment, effectively mitigating active-site poisoning. Collectively, these structural and interfacial features enable the Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalyst to achieve efficient propane oxidation with outstanding stability under humid and sulfur-containing conditions.

To further elucidate the water resistance mechanism of the catalysts, H₂O-TPD characterization was performed on Pt/Ni₁Co_0.5AlO_x and Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalysts, with results strongly corroborating the aforementioned catalytic performance trends. The H₂O-TPD curves revealed that the total desorption peak area for Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) was significantly smaller than that for Pt/Ni₁Co_0.5AlO_x, indicating that the core–shell structure with a ZSM-5 shell effectively reduced the total amount of adsorbed H₂O on the catalyst surface (Fig. 7a). This directly validates the prior conclusion: the ZSM-5 shell inhibits H₂O adsorption, thereby mitigating competitive adsorption between H₂O and reaction intermediates on propane/O₂/active sites (Fig. 7b). In contrast, Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) predominantly exhibited low-temperature desorption peaks, indicating weaker and reversible H₂O adsorption with minimal permanent damage to active sites. This aligns with its slight activity decay during water resistance testing and rapid recovery after dehydration. Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) exhibits fewer and more concentrated desorption peaks, attributed to the ZSM-5 shell's high Si/Al ratio reducing polar bond density while increasing non-polar Si–O–Si bonds, thereby weakening interactions between polar H₂O molecules and active sites. The hydrophobic Pt/ZSM-5 shell in Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) further impedes H₂O penetration and shields Pt and Co active sites from aqueous erosion, constituting the key to its exceptional H₂O stability. Collectively, H₂O-TPD results provide direct microscopic evidence for the water resistance mechanism of the core–shell catalyst, confirming that the ZSM-5 shell enhances water resistance by modulating the adsorption capacity, strength, and reversibility of H₂O.

Fig. 7 H₂O-TPD profiles (a) of Pt/Ni₁Co_0.5AlO_x and Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalysts. The schematic diagram of the water resistance mechanism of the ZSM-5 shell (b). SO₂-TPD profiles of Pt/Ni₁Co_0.5AlO_x and Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalysts (c). The schematic comparison showing how the ZSM-5 shell protects the active component from SO₂ poisoning (d).

To further elucidate the exceptional SO₂ tolerance of the core–shell catalysts, SO₂-TPD measurements were conducted on Pt/Ni₁Co_0.5AlO_x and Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) to complement the previously discussed catalytic performance and structural characterization (Fig. 7c and d). According to established taxonomies, low-temperature peaks (<300 °C) correspond to weakly adsorbed SO₂ at volatile sites, the mid-temperature peak (300–600 °C) indicates moderately adsorbed SO₂ at acidic or redox-active sites, while the high-temperature peak (>600 °C) reflects strongly bound SO₂ at irreversible sulfidated sites. As depicted in Fig. 7c, Pt/Ni₁Co_0.5AlO_x exhibits pronounced desorption peaks across the entire temperature range, with low-temperature desorption peaks predominating. This phenomenon confirms that unprotected Pt and Co sites exhibit strong adsorption of SO₂, consistent with their severe deactivation in SO₂ environments. In stark contrast, Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) exhibits negligible desorption at elevated temperatures, with low-to-medium temperature peaks accounting for over 90% of the total desorption area. These peaks correspond to SO₂ adsorption on weak-to-moderate Lewis acid sites within the ZSM-5 shell, where SO₂ is captured through weak interactions. in situ DRIFTS experiments further corroborate this mechanism: sulfate/sulfite species were detected on the ZSM-5 surface, with no Pt sulfidation being observed. Notably, Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) exhibits a faint desorption peak around 410 °C, indicating minor sulfate/sulfite formation. This phenomenon aligns closely with the catalyst's enhanced catalytic activity during SO₂ exposure, further validating its ability to mitigate sulfur poisoning through controlled SO₂ adsorption. This core–shell interface-driven adsorption mechanism explains why Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) preferentially adsorbs SO₂ within the shell layer, thereby shielding Pt⁰ and Co³⁺ from sulfidation and maintaining catalytic activity even under SO₂ exposure. In summary, the ZSM-5 shell forms a selective barrier via interfacially engineered acidic sites, confining SO₂ within the shell and preventing its diffusion to Pt and Co active sites. This confers exceptional sulfur resistance unattainable by bare Pt/Ni₁Co_0.5AlO_x.

To elucidate the atomic-level details of propane activation mechanisms, DFT calculations were employed to compare the adsorption energies of propane on Pt/NiCoAlO_x and NiCoAlO_x@Pt/ZSM-5 model surfaces. As shown in Fig. 8a, the adsorption energy of propane on the NiCoAlO_x@Pt/ZSM-5 surface is −0.52 eV, which is more negative than that on the Pt/NiCoAlO_x surface (−0.50 eV). A more negative adsorption energy indicates stronger interactions between propane and the catalyst surface, which favors the cleavage of the inert C–H bond. Fig. 8b and c present differential charge density plots for Pt/NiCoAlO_x and NiCoAlO_x@Pt/ZSM-5 models. These reveal strong pairwise interactions among the Pt, NiCoAlO_x, and ZSM-5 phases, with electron transfer between Pt and oxygen atoms on both NiCoAlO_x and ZSM-5. Fig. 8d elucidates the molecular-level reaction pathway for propane oxidation catalyzed on NiCoAlO_x@Pt/ZSM-5. Propane first adsorbs onto the catalyst surface. Pt⁰ sites on the Pt/ZSM-5 shell cleave the inert C–H bond, yielding propene as the first intermediate. The propylene is further oxidized to form acetone-like species (C₃H₆O), followed by a carboxylate intermediate (C₃H₆O₂). The formation of these oxygen-containing species was confirmed by in situ DRIFTS. The carboxylate intermediates were broken into smaller oxygen-containing species (CH₃O–, C₂H₃O–), which are subsequently fully oxidized to CO₂ and H₂O. The reaction pathway for the oxidative decomposition of propane on the Pt/NiCoAlO_x model is shown in Fig. S18. Additionally, we analyzed the Gibbs free energy changes for the oxidation of propane over Pt/NiCoAlO_x and NiCoAlO_x@Pt/ZSM-5. As depicted in Fig. 8e, the reaction traverses five intermediate states (IS1–IS5) and four transition states (TS1–TS4), with Gibbs free energy barriers (ΔG) quantified for each step.^64–66 The Gibbs free energy barrier (ΔG₁) for NiCoAlO_x@Pt/ZSM-5 is 1.35 eV, markedly lower than that for Pt/NiCoAlO_x (1.58 eV). This reduction indicates that the NiCoAlO_x@Pt/ZSM-5 structure promotes the activation of propane's initial C–H bond, consistent with our experimental observations. Compared to Pt/NiCoAlO_x's ΔG₂ of 1.25 eV, NiCoAlO_x@Pt/ZSM-5 exhibits a ΔG₂ of 1.06 eV. This further reduction in the energy barrier indicates that the ZSM-5 shell stabilizes the reaction intermediate through strong interactions at acid sites, thereby lowering the energy required for subsequent oxidation.⁶⁴ The ΔG₃ value for NiCoAlO_x@Pt/ZSM-5 (0.82 eV) is lower than that for Pt/NiCoAlO_x (0.98 eV), attributed to synergistic electronic modulation at the Pt/ZSM-5 interface. The ZSM-5 shell redistributes electrons on Pt, enhancing the reactivity of the adsorbed intermediate towards lattice oxygen from the CoNiAlO_x core. In the final deep oxidation step, the energy barrier for NiCoAlO_x@Pt/ZSM-5 (ΔG₄ = 1.01 eV) is lower than that for Pt/NiCoAlO_x (1.16 eV), thereby ensuring efficient conversion of the intermediate into CO₂ and H₂O.⁶⁵ The geometric structural parameters of propane adsorbed on Pt/NiCoAlO_x and NiCoAlO_x@Pt/ZSM-5 surfaces are shown in Table S2. The NiCoAlO_x@Pt/ZSM-5 surface exhibits greater elongation of C–C bonds and greater distortion of bond angles than in Pt/NiCoAlO_x, indicating that NiCoAlO_x@Pt/ZSM-5 exerts more pronounced structural distortion and bond activation effects on propane. This aligns with the preceding analysis of DFT adsorption energies and reaction energy barriers, providing a geometric explanation for NiCoAlO_x@Pt/ZSM-5's superior propane oxidation activity.

Fig. 8 The adsorption calculations of propane (a) on Pt/NiCoAlO_x and NiCoAlO_x@Pt/ZSM-5 model surfaces. Charge density difference plot for (b) Pt/NiCoAlO_x and (c) NiCoAlO_x@Pt/ZSM-5. The isosurface value is 0.01 e Bohr⁻³. Yellow is positive and blue is negative. The oxidative decomposition pathway of propane on NiCoAlO_x@Pt/ZSM-5 (d). Primitive steps and Gibbs free energy diagram of propane oxidation over Pt/NiCoAlO_x and NiCoAlO_x@Pt/ZSM-5 (e). The adsorption calculations of H₂O (f), density of states (g) and (h), the adsorption and dissociation calculations of O₂ (i), Projected DOS (j) and the calculation of SO₂ adsorption (k) on Pt/NiCoAlO_x and NiCoAlO_x@Pt/ZSM-5 model surfaces.

To gain deeper insight into the water resistance mechanism of the catalyst, we compared the adsorption energies of H₂O on Pt/NiCoAlO_x and NiCoAlO_x@Pt/ZSM-5, and the results are shown in Fig. 8f. The adsorption energy of H₂O on Pt/NiCoAlO_x (−0.81 eV) is markedly more negative than that on NiCoAlO_x@Pt/ZSM-5 (−0.52 eV), directly accounting for the superior water resistance of NiCoAlO_x@Pt/ZSM-5. In contrast, Pt/NiCoAlO_x contains more polar metal hydroxyl sites, leading to intense competition between H₂O and propane for Pt active sites. Further analysis of surface energy changes via density of states (DOS) modelling is presented in Fig. 8g and h. Pt/NiCoAlO_x and NiCoAlO_x@Pt/ZSM-5 exhibit distinct density of states distributions owing to the structural differences between the spinel NiCoAlO_x and ZSM-5 frameworks. Nevertheless, both systems display rich band structures near the Fermi level, indicating that both the spinel structure of NiCoAlO_x and the ZSM-5 framework facilitate electron transfer at the surface.⁶⁶ To elucidate the activation mechanism of oxygen species on Pt/NiCoAlO_x and NiCoAlO_x@Pt/ZSM-5, we analyzed the adsorption and dissociation of O₂ on both models (Fig. 8i). The O₂ adsorption energy on NiCoAlO_x@Pt/ZSM-5 is −0.32 eV, lower than that on Pt/NiCoAlO_x (−0.60 eV). This indicates that the adsorption strength of oxygen species on NiCoAlO_x@Pt/ZSM-5 is favorable, preventing dissociation from being hindered by an excessively stable O–O bond. In contrast, O₂ exhibits stronger adsorption on Pt/NiCoAlO_x, potentially leading to slower O–O bond cleavage. Fig. 8j analyzes the Projected Density of States (PDOS) for Pt, the primary active component in the model structures. It is evident that under the combined influence of NiCoAlO_x and ZSM, the d-band center of Pt in NiCoAlO_x@Pt/ZSM-5 (−1.004 eV) shifts towards the Fermi level compared to Pt/NiCoAlO_x (−1.324 eV). This indicates that the synergistic interaction between NiCoAlO_x and ZSM elevates the energy of surface Pt. Bader charges corroborate the PDOS findings (Table S3). The triphasic electron transfer between the Pt/ZSM structure and NiCoAlO_x is discernible, ultimately leading to macroscopic electron transfer from Co and Al in NiCoAlO_x to Pt and Ni. This significantly enhances catalytic performance.^64,66

To elucidate the molecular mechanisms underlying the SO₂ resistance of Pt/NiCoAlO_x and NiCoAlO_x@Pt/ZSM-5, we analyzed the Gibbs free energy curves for SO₂ adsorption and oxidation on the surfaces of Pt/NiCoAlO_x and NiCoAlO_x@Pt/ZSM-5 (Fig. 8k). The SO₂ adsorption energy on NiCoAlO_x@Pt/ZSM-5 is −0.44 eV, lower than −0.52 eV observed on Pt/NiCoAlO_x. SO₂ is captured by the ZSM-5 shell, avoiding the formation of irreversible bonds, in stark contrast to the excessively strong SO₂ adsorption on Pt/NiCoAlO_x. The free energy barrier for SO₂ oxidation (ΔG from SO₂ (g) to SO₂–O*) in the iCoAlO_x@Pt/ZSM-5 system is 0.70 eV, markedly higher than that of Pt/NiCoAlO_x (0.13 eV). This elevated barrier inhibits the formation of SO₃* (an irreversible Pt sulfide precursor) on the NiCoAlO_x@Pt/ZSM-5 surface. Conversely, the low energy barrier in Pt/NiCoAlO_x promotes SO₂ oxidation to SO₃*, which readily reacts with Pt to form deactivated Pt-S species. The adsorption energy for SO₃* on NiCoAlO_x@Pt/ZSM-5 is −0.24 eV, substantially lower than the −0.48 eV observed on Pt/NiCoAlO_x. The weak adsorption of SO₃* on NiCoAlO_x@Pt/ZSM-5 ensures that any formed SO₃ is readily desorbed or captured by the ZSM-5 shell, thereby preventing its accumulation at Pt active sites.

5. Analysis and discussion about the relationship between textural properties and catalytic performance of the catalyst

We systematically analyzed the intrinsic mechanisms underlying the exceptional catalytic activity, resistance to H₂O poisoning, and resistance to SO₂ poisoning exhibited by the Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) and Ni₁Co_0.5AlO_x@Pt/ZSM-5(5%) core–shell catalysts. The Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalyst demonstrated optimal activity. The Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalyst possesses the highest contents of Pt⁰, Co³⁺, and O_ads, all of which play irreplaceable roles in the propane oxidation reaction. The higher O_ads content in the Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalyst enables faster conversion of the propane intermediate, with highly mobile and active O_ads directly participating in the deep oxidation of the carboxylate intermediate to CO₂ and H₂O. The 3 wt% Pt/ZSM-5 shell thickness directly influences diffusion resistance for propane and O₂ towards active sites, constituting a key factor that distinguishes the activity of Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) from that of other catalysts. Conversely, medium-strong acid sites originating from ZSM-5-bridged Si–OH–Al groups and unsaturated Co³⁺/Ni³⁺ coordination in the core region promote C–H bond cleavage by donating protons to propane. The lower E_a value of Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) confirms that abundant weak and medium-strong acid sites reduce the energy barrier for C–H bond activation.

The mechanisms underlying the resistance to H₂O poisoning in Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) and Ni₁Co_0.5AlO_x@Pt/ZSM-5(5%) were further explored in depth. The hydrophobicity of the Pt/ZSM-5 shell constitutes the primary defence mechanism against H₂O adsorption. This shell forms a physical barrier that prevents H₂O diffusion into the Ni₁Co_0.5AlO_x core, thereby safeguarding the redox active species from degradation. The non-polar Si–O–Si bonds exhibit weak interactions with polar H₂O molecules. In contrast, the exposed Pt/Ni₁Co_0.5AlO_x surface is rich in polar Al–OH hydroxyl groups, rendering it highly susceptible to H₂O adsorption. Compared with bare Pt/Ni₁Co_0.5AlO_x, the Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) and Ni₁Co_0.5AlO_x@Pt/ZSM-5(5%) catalysts show weaker water adsorption, which reduces the number of available H₂O adsorption sites on their surfaces. The Pt⁰ content on the surfaces of Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) readily deactivate under aqueous conditions, progressively oxidizing to Pt²⁺ or Pt⁴⁺, whereas the ZSM-5 shell significantly mitigates this oxidation reaction. This explains why the T₉₀ of Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) remains lower than that of the bare Pt/Ni₁Co_0.5AlO_x catalyst under aqueous conditions.

We investigated the sulfur tolerance of the Ni₁Co_0.5AlO_x@Pt/ZSM-5 catalyst. The Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalyst demonstrated exceptional SO₂ tolerance, exhibiting enhanced activity during SO₂ exposure, whereas the bare catalyst's activity declined to 44.2%. This tolerance stems from the SO₂ trapping and active site protection mechanisms within the shell layer. Acid sites within the ZSM-5 shell preferentially adsorb SO₂, thereby reducing its contact with Pt active sites. Even in the presence of SO₂, the Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalyst maintained the normal propane oxidation pathway, avoiding activity loss due to pathway disruption. The minor sulfate species formed on the Pt/ZSM-5 shell surface act as strong Lewis acids, further promoting propane adsorption and C–H bond activation. This explains the transient increase in activity observed for Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) during SO₂ exposure.

Based on the above discussion and analysis, a correlation between the structure and performance of the Ni₁Co_0.5AlO_x@Pt/ZSM-5(x%) (x = 3, 5) catalysts can be summarized, arising from synergistic effects between the core and shell. The Ni₁Co_0.5AlO_x core provides abundant Co³⁺ and Ni³⁺ species and active oxygen species, whilst the Pt/ZSM-5 shell supplies Pt⁰ active sites, a hydrophobic protective layer, and SO₂ capture sites. The core–shell interface facilitates electron transfer and oxygen species exchange, thereby enhancing overall catalytic performance. The 3 wt% and 5 wt% Pt/ZSM-5 shells strike a balance between activity and stability, rendering Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) suitable for low-temperature, high-activity, harsh industrial environments. More satisfactorily, compared to previously reported platinum-based catalysts for propane oxidation, Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) and Ni₁Co_0.5AlO_x@Pt/ZSM-5(5%) catalysts demonstrate significant advantages in both activity and resistance to poisoning. This confirms that the supramolecular assembly strategy for core–shell catalysts represents an effective approach to overcoming industrial application bottlenecks for Pt-based VOC oxidation catalysts.

Although the Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalyst exhibits excellent activity and resistance to water and sulphur in propane oxidation, it still has certain limitations that warrant further investigation. The catalyst's optimal performance is observed under low to moderate concentrations of H₂O and SO₂. Its stability at higher concentrations of poisons or during long-term industrial operation remains to be verified. For instance, the preparation process involves hydrothermal coating and precise control of the shell thickness; the process costs and reproducibility for scaled-up production require optimization. In this study, propane was used as a model alkane reactant; the catalyst's applicability to other VOCs, such as toluene and chlorinated hydrocarbons, has not yet been investigated. We will conduct systematic research on the above issues in the future to further advance the practical industrial application of this core–shell catalytic system.

6. Conclusion

In summary, we rationally designed and prepared a series of Ni₁Co_0.5AlO_x@Pt/ZSM-5 core–shell catalysts by supramolecular assembly coupled with hydrothermal coating to address the key issue of poor H₂O/SO₂ resistance in Pt-based catalysts for propane catalytic oxidation. The catalytic activity and anti-poisoning performance were improved. The Si–O–Si linkages in the ZSM-5 shell exhibited low affinity for polar H₂O molecules, significantly enhancing hydrophobicity and thereby suppressing H₂O adsorption. Simultaneously, acidic sites within the ZSM-5 shell preferentially adsorb SO₂, thereby reducing its contact with Pt active sites. This enables the Ni₁Co_0.5AlO_x@Pt/ZSM-5 catalyst to exhibit outstanding sulfur tolerance. The shell acts not only as a physical barrier preventing H₂O and SO₂ from reaching active sites, but also as a chemical interface that promotes the formation and stabilization of high-valence metal ions such as Pt⁴⁺, Co³⁺, Ni³⁺ and lattice oxygen. The Ni₁Co_0.5AlO_x@Pt/ZSM-5(3%) catalyst exhibits optimal catalytic activity and SO₂ tolerance, along with improved H₂O resistance. The reason is attributed to the highest contents of Pt⁰, Co³⁺ and adsorbed oxygen, which enhanced redox capability and acid sites, synergistically facilitating the adsorption and deep oxidation of propane. These findings provide a promising strategy for designing Pt-based catalysts with enhanced activity and stability in H₂O- and SO₂-containing environments.

Conflicts of interest

The authors confirm that neither personal affiliations nor financial stakes had any impact on the content of this article.

Data availability

The data that support the findings of this study are available in the supplementary information (SI) of this article. Supplementary information: results from TEM, HRTEM, catalytic activity, reaction kinetics calculations, XRD, BET, H₂-TPR, O₂-TPD, NH₃-TPD, in situ DRIFTS and DFT calculations. See DOI: https://doi.org/10.1039/d6ey00068a.

Acknowledgements

This work was supported by the Science and Technology Program of Chengguan District (2024-rc-4), the Key Research and Development Program of Gansu Province (24YFFA011), the West Light Foundation of Chinese Academy of Sciences (xbzg-zdsys-202318), and the Shandong Provincial Natural Science Foundation (No. ZR2025QC98).

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Footnote

† These authors contributed equally: Shixing Wu, Qian Peng.

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