Fabrication and catalytic properties of nanorod-shaped (Pt–Pd)/CeO₂ composites

Abstract

Nanorod-supported (Pt–Pd)/CeO₂ catalysts were synthesized by a simple method of dealloying Al_91.7Ce₈ Pt_XPd_0.3−X (X = 0, 0.075, 0.1, 0.15, 0.2, 0.3) alloy ribbons. SEM and TEM characterization implied that after calcination treatment, the achieved resultants exhibited interspersed nanorod structures with a rich distribution of nanopores. Catalytic tests showed that the (Pt_0.1–Pd_0.2)/CeO₂ catalyst calcined at 300 °C exhibited the highest catalyst activity for CO oxidation when compared with other catalysts prepared at different noble metal ratios or calcined at other temperatures, whose complete reaction temperature was as low as 100 °C. The outstanding catalytic performance is ascribed to the stable framework structure, rich gas pathways and collaborative effect between the noble Pt and Pd bimetals.

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1. Introduction

Because of the flammability and easy-explosion feature of CO, which is generated in daily life and industrial production, it is important to eliminate CO.¹ Even though the oxidation of CO to CO₂ is a good method to eliminate CO pollution, it always requires large energy consumption and strict conditions during the process. Catalytic oxidation of CO is an efficient method to get rid of CO pollution at low/room temperatures.^2–4 As the earliest proposed type of catalysts, noble metals such as Pd, Pt, Rh, and Au exhibit high activity for CO oxidation.^5–7 Pt group metal-based catalysts play an important role in the catalytic field because of their strong activity and wide applications, but the high price and low efficiency of a single atom of Pt hinder its further development.⁸ Partial introduction of Pd, a cheaper noble metal into Pt can not only reduce the cost but can also enhance catalytic efficiency and avoid CO poisoning.^9,10 Suzanne Giorgio et al. achieved partial institution of Pt to Pd and obtained core–shell structured Pt–Pd nanotubes.¹¹ The Garcia's team synthesized bimetallic clusters by doping Pd into Au₂₅ and demonstrated the strongly enhanced CO conversion of bimetallic catalysts.¹²

Ceria (CeO₂), a rare metal oxide with abundant reserves on the earth, is known to be a good supporting oxide for catalysis due to its outstanding store/release oxygen ability through a reversible and fast Ce⁴⁺/Ce³⁺ reaction.^13–15 Moreover, the low energy for oxygen vacancy formation and oxygen diffusion as well as superior thermal stability makes CeO₂ an ideal material for gas catalytic usage. CeO₂-noble metal-based catalysts with rich morphologies and facets such as nanorods,¹⁶ nanocubes,¹⁷ particles,¹⁸ and octahedra,¹⁹ have been widely reported. The Neyman's group²⁰ synthesized Pt/CeO₂ catalyst with different Pt loading by a co-precipitation method and observed the CO oxidation activity at low temperatures. Xu and his collaborators²¹ loaded Au on ZIF-8 successfully through the solid grinding method, and the obtained Au@ZIF-8 catalyst showed good activity. However, the preparation conditions for these catalysts usually need high economic costs with low yield, and their practical and industrial production is still a challenge.

Recently, the dealloying method has generated wide attraction for the preparation of nanomaterials because of its simple and effective fabrication features.^22,23 The morphology and size of materials can be controlled by changing corrosion or post-treatment conditions or by adjusting the composition and content of alloys. The CeO₂-noble metal-based catalysts, such as Rh/CeO₂,²⁴ Au/CeO₂,²⁵ and CeO₂-transition metal (oxide)-based catalysts such as baize-like NiO/CeO₂,²⁶ Cu/CeO₂,²⁷ have been successfully fabricated by a dealloying method and displayed outstanding catalytic activity for CO oxidation because of the large surface area and high porosity of the porous structured materials. However, the influence and mechanism of bimetal loading on CeO₂ need further investigation.

Inspired by the above considerations, herein, the nanorod-supported (Pt–Pd)/CeO₂ catalysts with varied Pt/Pd ratios were prepared by dealloying Al–Ce–Pt–Pd alloy ribbons followed by corrosion and calcination treatment for catalytic CO oxidation. Results show that the obtained samples exhibited stable framework structure and large amounts of pathways for gas entry/exit due to the interspersed nanorods and the joint effect of Pt/Pd as well as the formation of rich nanopores among nanorods. The (Pt_0.1–Pd_0.2)/CeO₂ catalyst exhibited the best catalytic performance with 50% and 99% conversion at temperatures (T₅₀, T₉₉) as low as 75 °C and 100 °C, respectively.

2. Experimental section

2.1 Material preparation

The precursor alloy ingots of Al₉₂Ce₈, Al_91.7Ce₈Pt_X–Pd_0.3−X (X = 0, 0.075, 0.1, 0.15, 0.2, 0.3) were fabricated from pure metal Al, Ce, Pt, Pd by arc-melting under high-purity Ar atmosphere. The obtained alloy ingots were then remelted in a quartz tube and blown onto a copper cooling roll to achieve an alloy ribbon with a width of 4–6 mm and a thickness of 40–70 μm. Next, the quenched ribbons were immersed into 20 wt% NaOH aqueous solution at room temperature for 2 hours until no bubbles generated and then further immersed at 353 K for 10 hours. Ultimately, the de-alloyed ribbons were dried and calcined at 473–773 K for 2 h in a pure O₂ environment. The samples derived from Al–Ce–Pt–Pd precursors were denoted as (Pt_X–Pd_0.3−X)/CeO₂ (X = 0.075, 0.1, 0.15, 0.2). The subscript number of Pt and Pd in (Pt_X–Pd_0.3−X)/CeO₂ refers to their respective atomic proportion in the Al_91.7Ce₈Pt_XPd_0.3−X precursor.

2.2 Characterization

The phase composition was investigated by X-ray diffractometry (XRD, Bruker D8 Advance). The surface morphologies and microstructures of the fabricated catalysts were characterized by field emission scanning electron microscopy (FESEM, JEOL, JSM-7000F) and high-resolution transmission electron microscopy (HRTEM, JEOL, JEM-2100). EDS analysis and mapping were performed by scanning transmission electron microscopy (STEM, FEI-200) equipped with an Oxford Instrument's EDS spectrometer. The element composition and valence state were measured using an X-ray photoelectron spectrophotometer (XPS, ESCALAB Xi+). Nitrogen sorption isotherms and specific surface area were measured on a Micromeritics ASAP 2020 instrument at 77 K, and the pore size distributions were obtained from the desorption branch of the isotherm using the Barrett–Joyner–Halenda algorithm. Raman spectra were collected using an HR 800 fully automatic laser Raman spectrometer with a laser wavelength of 633 nm. Hydrogen temperature-programmed reduction (H₂-TPR) measurements were performed on an Auto ChemTM II 2920 chemisorption analyzer.

2.3 Catalytic evaluations

The catalytic performance of the fabricated catalysts was studied using a tube furnace with a fixed bed flow reactor under atmospheric pressure. A 100 mg tested sample was placed into the reactor and fixed with quartz wool. The feeding gas with a mixture of 1% CO, 10% O₂, and 89% N₂ (volume fraction) was injected into the test system at a flow rate of 100 mL min⁻¹ and space velocity of 60 000 h⁻¹. The intake and outlet gases were analysed using an Anglit 7890B gas chromatograph equipped with a hydrogen flame detector (FID). The CO conversion can be calculated by eqn (1)in which C_in and C_out represent the concentration of CO entering and exhausting the reactor, respectively.

3. Results and discussion

In this work, a facile combined dealloying and calcination method is proposed to fabricate a nanorod-supported bimetal/CeO₂ framework structure (Fig. S1†). The XRD patterns of the melt-spun ribbon precursor and de-alloyed Al_91.7Ce₈Pt_0.1Pd_0.2 ribbons are shown in Fig. S2,† while the de-alloyed ribbons with varied Pt/Pd content after calcination treatment are displayed in Fig. 1. As observed in Fig. S2,† the melt-spun ribbons consist of α-Al, Al₉₂Ce₈, and Al₄Ce phases; after the de-alloying treatment, the peaks representing α-Al, Al₉₂Ce₈ and Al₄Ce disappeared, while the new diffraction peaks corresponding to CeO₂ were detected, which may be due to the fact that the precursor ribbons decomposed during the de-alloying procedure. The XRD patterns of the four de-alloyed Al–Ce–Pt–Pd ribbons after calcination treatment are presented in Fig. 1; the diffraction peaks located at 28.64°, 33.06°, 47.56° 56.22° correspond to (111), (200), (220), (311) planes, respectively, of cubic CeO₂ (PDF# 89-8436).^28,29 No diffraction peaks corresponding to Al, Pt, and Pd were detected in the (Pt_X–Pd_0.3−X)/CeO₂ samples (Fig. 1), demonstrating that Al has been completely removed from the material system. What is more, Pt and Pd were also not detected, which could be due to the low content and high dispersity of the two noble elements in the material system as well as the poor crystallinity of the samples.

Fig. 1 XRD patterns of (Pt_X–Pd_0.3−X)/CeO₂ (X = 0.075, 0.1, 0.15, 0.2) calcined at 573 K.

The surface microstructures of the de-alloyed Al–Ce–Pt–Pd with varied Pt/Pd content calcined at 573 K were characterized by SEM (Fig. 2). The samples are composed of nanorods, which intersperse and stack each other to form a nanorod-supported framework structure with rich nanopores distributed among them. The diameter of nanorods is 5–10 nm. As the total content of Pt and Pd in Al–Ce–Pt–Pd alloy keeps 0.3 at%, and when the Pt content is increased to 0.075 at% (Fig. 2a), 0.1 at% (Fig. 2b), 0.15 at% (Fig. 2c) and 2 at% (Fig. 2d), respectively, the surface microstructure of the sample stayed similar and did not change significantly. However, the interspersed nanorods help stabilize the framework structure of samples; the existence of rich nanopores can provide more pathways for the gas to enter/exit, thus enhancing the catalytic oxidation rate.²⁴ The SEM images of (Pt_0.1–Pd_0.2)/CeO₂ calcined at different temperatures are shown in Fig. S3.† As observed, even though the nanorods of (Pt_0.1–Pd_0.2)/CeO₂ are coarsened after calcining at 300 °C, and 500 °C, when compared with samples without the calcination treatment, their overall morphology remained unchanged, implying outstanding thermal stability.

Fig. 2 The SEM images of (Pt_X–Pd_0.3−X)/CeO₂ X = (a) 0.075, (b) 0.1, (c) 0.15, (d) 0.2.

TEM studies were conducted to obtain a more detailed microstructure information of (Pt_X–Pd_0.3−X)/CeO₂. As observed from the TEM images of (Pt_0.075–Pd_0.225)/CeO₂ (Fig. 3a), (Pt_0.1–Pd_0.2)/CeO₂ (Fig. 3c), (Pt_0.15–Pd_0.15)/CeO₂ (Fig. 3e), (Pt_0.2–Pd_0.1)/CeO₂ (Fig. 3g), the black nanoparticles with an average diameter of 3–5 nm are homogeneously loaded onto the surface of nanorod; the nanorod with an average diameter of 10 nm pile up on each other to form an interconnected structure, which is in line with SEM results. In the HRTEM images shown in Fig. 3b, d, f and h, the interplanar space of 0.32 nm corresponds to the (111) plane of the cubic structure of CeO₂ nanorods; the lattice fringe widths of 0.229 nm and 0.264 nm for the black particles semi-inlaid onto nanorod corresponded to the (111) and (101) planes of Pt and PdO, respectively, demonstrating that Pt and PdO were successfully loaded onto the CeO₂ nanorod surface. Noteworthy, the introduced Pt and PdO were close to each other, which helps the synergistic effect between them and promotes the respective adsorption and oxidation of CO during the catalytic process, thus contributing to the enhancement of the catalytic performance of (Pt–Pd)/CeO₂ catalysts.

Fig. 3 The TEM and HRTEM images of (a and b) (Pt_0.075–Pd_0.225)/CeO₂, (c and d) (Pt_0.1–Pd_0.2)/CeO₂, (e and f) (Pt_0.15–Pd_0.15)/CeO₂, (g and h) (Pt_0.2–Pd_0.1)/CeO₂.

STEM mapping characterization was utilized to analyze the distribution of elements on the surface of CeO₂ nanorods in (Pt_0.1–Pd_0.2)/CeO₂ catalyst and the results are shown in Fig. 4. As clearly observed from Fig. 4a, Pt, and PdO are in situ loaded on the surface of CeO₂ nanorods in the form of nanoparticles (indicated by white arrows). Fig. 4b–d further demonstrates that the sample consists of Ce, Pt, and Pd elements, and they are homogeneously distributed among nanorods.

Fig. 4 (a) The STEM image of (Pt_0.1–Pd_0.2)/CeO₂ and element mapping of (b) Ce, (c) Pt, (d) Pd.

The N₂ adsorption–desorption studies were conducted to determine the surface area, pore size, and distribution in the samples. As shown from the nitrogen adsorption–desorption isotherms of four (Pt–Pd)/CeO₂ catalysts shown in Fig. 5a, all of them exhibit type-IV isotherm with a type-H3 hysteresis loop at a relative pressure range of 0.65–1.0 P/P₀, implying the existence of the mesoporous structure.³⁰ The BET surface areas of (Pt_0.075–Pd_0.225)/CeO₂, (Pt_0.1–Pd_0.2)/CeO₂, (Pt_0.15–Pd_0.15)/CeO₂, (Pt_0.2–Pd_0.1)/CeO₂ are 122.50, 120.19, 136.43, 132.54 m² g⁻¹, respectively. What is more, the BHJ pore-size distribution curves in Fig. 5b present a uniform pore-size distribution located at 10–13 nm, further illustrating the mesoporous structure feature of the four samples.³¹ The pore volumes for (Pt_0.075–Pd_0.225)/CeO₂, (Pt_0.1–Pd_0.2)/CeO₂, (Pt_0.15–Pd_0.15)/CeO₂, (Pt_0.2–Pd_0.1)/CeO₂ are 0.33, 0.33, 0.44, 0.34 cm³ g⁻¹. Obviously, all of the de-alloyed samples after the calcination treatment displayed higher specific surface area and lower pore diameter when compared with that of the pure CeO₂ nanorod framework reported in the previous work.³² In addition, although the added proportion of Pt and Pd varies as the total content stays unchanged, the partial replacement of Pt with Pd did not affect the physical structure parameters of the material significantly, so the specific surface area and porosity of the four samples are quite similar.

Fig. 5 (a) Nitrogen adsorption–desorption isotherms and (b) the BHJ pore size distribution of the de-alloyed (Pt–Pd)/CeO₂ nanorods.

The chemical valence of the surface elements was confirmed using XPS and the typically fitted Ce 3d, Pt 4f, Pd 3d, O 1s XPS spectra of the (Pt_0.1–Pd_0.2)/CeO₂ catalyst as obtained by the Gaussian fitting method, and presented in Fig. 6a–d, respectively. In Fig. 6a, the Ce 3d spectrum is fitted with six spin–orbit split doublets and two shake-up satellites. The binding energies at 881.9 eV, 888.2 eV, and 897.7 eV for Ce 3d_5/2 and 900.4 eV, 907.3 eV, 916.2 eV for Ce 3d_3/2 are characteristic of Ce⁴⁺, and the peaks located at 884.5 eV, 903.3 eV are assigned to Ce³⁺.^30,33 Since the concentration of Ce³⁺ can be reflected from the integrated areas of peaks, the surface Ce³⁺ concentration of total Ce on the (Pt_0.1–Pd_0.2)/CeO₂ nanorod framework is 18.26% (Fig. 6a). In Fig. 6b, the two peaks at 70.9 eV and 74.2 eV are assigned to Pt⁰,³⁴ while the binding energies at 72.1 eV for Pt 4f_7/2 and 76.1 eV for Pt 4f_5/2 correspond to Pt²⁺.³⁵ Similarly, the 63.3% percentage of Pt⁰ can be achieved by calculating the fitting areas of Pt⁰/(Pt⁰ + Pt²⁺). In the Pd 3d spectrum shown in Fig. 6c, both metallic Pd and ionic Pd²⁺ can be clearly detected in (Pt_0.1–Pd_0.2)/CeO₂ catalyst. The peaks at 336.2 eV and 341.2 eV correspond to Pd 3d_5/2 of Pd⁰; the binding energies at 337.2 eV for Pd 3d_5/2 and 342.5 eV for Pd 3d_5/2 belong to Pd²⁺.³⁶ The Pd²⁺ concentration of total Pd is 71% and the ratio between Pd⁰ and Pd²⁺ is around 3 : 7. For the O 1s spectrum in Fig. 6d, the peaks at 529.2 eV, 531.2 eV correspond to lattice oxygen (O_lat), surface adsorbed oxygen (O_sur), respectively.³⁷ The calculation results show that the ratio of O_sur can reach as high as 31%. Since O_sur with better activity can stabilize the sample structure and promote the catalytic oxidation rate, the high ratio of O_sur in (Pt_0.1–Pd_0.2)/CeO₂ is beneficial for enhancing the catalytic property of (Pt–Pd)/CeO₂.

Fig. 6 XPS spectra of (a) Ce 3d, (b) Pt 4f, (c) Pd 3d, (d) O 1s of the (Pt_0.1–Pd_0.2)/CeO₂ catalyst.

Raman studies were conducted to further illustrate the molecular structure of the samples. Four kinds of (Pt–Pd)/CeO₂ catalysts with varied Pt/Pd ratios, an apparent peak located at 456 cm⁻¹ can be observed (Fig. 7a), which is attributed to the F_2g vibrational mode of CeO₂ originating from the breathing mode of oxygen anions around Ce cations.^38,39 Compared with the Raman result of pure CeO₂ shown in Fig. S4,† the peak intensity of (Pt–Pd)/CeO₂ catalysts is greatly decreased, and the diffraction location is shifted from 459 cm⁻¹ to 456 cm⁻¹, which is due to the generation of more grain boundaries brought from grain refinement after the addition of Pt and Pd nanoparticles into the material system. H₂-TPR measurements were also adopted to investigate the reducibility of samples, as shown in Fig. 7b. For (Pt_0.075–Pd_0.225)/CeO₂, (Pt_0.1–Pd_0.2)/CeO₂, (Pt_0.15–Pd_0.15)/CeO₂ and (Pt_0.2–Pd_0.1)/CeO₂ catalysts, the H₂ consumption peaks were located around 110–120 °C and are assigned to Pt and Pd nanoparticles; the strong peak at around 470 °C is related to active oxygen species of CeO₂, whereas the reduction peaks at 700–800 °C are bonded to lattice oxygen of CeO₂ that is not closely related to catalytic capacity.^29,40 By contrast, the integrated peak area of active oxygen for (Pt_0.1–Pd_0.2)/CeO₂ and (Pt_0.15–Pd_0.15)/CeO₂ is significantly higher than that of the other two catalysts, revealing their higher reducibility and superior catalytic performance. Notably, only a reduction peak at 275 °C is observed for the (Pt_0.1–Pd_0.2)/CeO₂ catalyst, which may be related to the ionic state of Pt.

Fig. 7 (a) Raman spectra and (b) H₂-TPR profile of (Pt–Pd)/CeO₂ nanorod supported framework.

The catalytic performance of the (Pt–Pd)/CeO₂ nanorod-supported framework catalysts with varied Pt/Pd content towards CO catalytic oxidation is displayed in Fig. 8. For Pt_0.3/CeO₂ prepared from de-alloyed Al_91.7Ce₈Pt_0.3 calcined at 573 K, the 50% catalytic CO oxidation temperature (T₅₀) and CO complete conversion temperature (T₉₉) are 91 °C and 113 °C, respectively, which are much better than those for pure CeO₂ calcined at 573 K (T₅₀ = 235 °C, T₉₉ = 320 °C). The percentage of Pd in the system was continuously increased and when Pt/Pd = 0.2 : 0.1, the catalytic properties were further improved with T₅₀ and T₉₉ decreasing to 83 °C and 110 °C, respectively. The catalytic performance of the catalyst was the best when Pt/Pd = 0.1 : 0.2, and corresponding 50% and 99% CO conversion temperatures reached as low as 75 °C and 100 °C, respectively. The three repeated catalytic performance tests demonstrate the reproducibility of the (Pt_0.2–Pd_0.1)/CeO₂ catalyst (Fig. S5†). By further improving the ratio of Pd to Pt : Pd = 1 : 3, the catalytic performance decreased (T₅₀ = 83 °C, T₉₉ = 130 °C). Noteworthily, for (Pt_0.1–Pd_0.2)/CeO₂ catalyst, the temperature difference between T₅₀ and T₉₉ is 25 °C, which is smaller than that for catalysts at other Pt/Pd ratios and significantly better than that for pure CeO₂ (80 °C), implying superior catalytic property of (Pt–Pd)/CeO₂ (Fig. 8a). The influence of calcination temperature on the CO conversion rate is also discussed and the data are shown in Fig. 8b. The total CO conversion temperatures of (Pt_0.1–Pd_0.2)/CeO₂ at calcination temperatures of 0 °C, 200 °C, 300 °C, 400 °C, 500 °C is 130 °C, 100 °C, 100 °C, 110 °C, 130 °C, respectively, revealed that the catalytic activity is premium at an annealing temperature of 300 °C. The catalytic activity of (Pt_0.1–Pd_0.2)/CeO₂ also surpasses that of the state-of-the-art CeO₂-based catalysts reported in the literature, as shown in Table S1.^41–45 †

Fig. 8 (a) CO conversion as a function of reaction temperature over the (Pt_0.075–Pd_0.225)/CeO₂, (Pt_0.1–Pd_0.2)/CeO₂, (Pt_0.15–Pd_0.15)/CeO₂ and (Pt_0.2–Pd_0.1)/CeO₂ catalysts; (b) the (Pt_0.1–Pd_0.2)/CeO₂ catalyst prepared from de-alloyed Al_91.7Ce₈Pt_0.1Pd_0.2 calcined at different temperatures.

Fig. 9a explores the influence of O₂ concentration in the feed gas on the catalytic performance of (Pt_0.1–Pd_0.2)/CeO₂. The test temperature was maintained at 373 K with a flow rate 100 mL min⁻¹. When 10% O₂ was initially infused into the system, the CO conversion rate could reach 99% because of the sufficient O₂ environment; the CO conversion rate was reduced first and then kept stable at 7% when the O₂ supply was suddenly decreased to zero, which may be ascribed to the existence of surface lattice oxygen that can migrate to active sites and combine with adsorbed CO to form oxygen vacancies. However, the CO conversion rate increases in poor oxygen conditions (0.5–1% O₂) and then recovers to the initial 99% value and remained unchanged when O₂ was resupplied into the feed gas, implying the superior catalytic CO oxidation property of (Pt_0.1–Pd_0.2)/CeO₂. The long-term stability and anti-CO₂/H₂O poisoning ability were also investigated and the data are displayed in Fig. 9b. The (Pt_0.1–Pd_0.2)/CeO₂ catalyst possesses a 98% conversion rate under the mixed atmosphere of 1% CO, 10% O₂, 89% N₂, 10% H₂O and remained stable without degradation after 70 h of successive reaction; when 5% CO₂ was injected into the infused gas, the adsorption of CO per unit time can be reduced due to the existence of CO competitive adsorption on the surface of (Pt_0.1–Pd_0.2)/CeO₂ nanorods, but the CO conversion rate was still maintained around 90% after 60 h, further demonstrating the superior stable catalytic performance and water resistance of the (Pt_0.1–Pd_0.2)/CeO₂ catalyst.

Fig. 9 (a) Catalytic performance under varied oxygen concentrations and (b) long-term stability of the (Pt_0.1–Pd_0.2)/CeO₂-573 K catalyst.

A possible mechanism for catalytic CO oxidation on (Pt–Pd)/CeO₂ catalyst is proposed and presented in Scheme 1. Mesoporous structured (Pt–Pd)/CeO₂ catalysts with a high specific surface area can be obtained by introducing Pt and Pd in various proportions. High specific surface area can bring more active sites and provide sufficient reaction paths for catalysis. The (Pt–Pd)/CeO₂ catalyst contains a high concentration of Ce³⁺ ions and active oxygen atoms; the highly concentrated Ce³⁺ can adsorb the required active oxygen on the catalytic interface, which is conducive for the formation of the active centres at the interface. The catalytic performance of the catalyst reached optimum when the same amounts of Pt and Pd were introduced into Al–Ce precursor alloys, which is attributed to the synergetic effect among Pt and PdO nanoparticles, as well as Pt/PdO and CeO₂ nanorods. In the catalytic process, CO is adsorbed onto the surface of Pt and PdO and reacts with oxygen species, which contributes to the formation of CO₂ and oxygen vacancies. The addition of Pt and PdO can accelerate the migration rate of oxygen species, and produce active oxygen species that can combine with activated CO quickly, then the catalytic rate and catalytic performance are enhanced.

Scheme 1 A possible mechanism for catalytic CO oxidation on (Pt–Pd)/CeO₂ catalyst.

4. Conclusions

In summary, the nanorod-supported nanoporous (Pt–Pd)/CeO₂ catalysts were prepared through a novel dealloying method and calcination treatment. The obtained (Pt–Pd)/CeO₂ prepared from Al_91.7Ce₈Pt_X–Pd_0.3−X (X = 0, 0.075, 0.1, 0.15, 0.2, 0.3) exhibits an interspersed nanorod structure with rich nanopores distributed among them. The catalytic performance reaches best with a T₅₀ temperature of 75 °C and total reaction temperature as low as 100 °C when the Pt/Pd ratio is 0.1 : 0.2. It is believed that the robust framework structure and the synergistic effect of Pt, Pd as well as rich nanopores among nanorods contribute to the high catalytic activity of (Pt–Pd)/CeO₂. These results provide new ideas for the fabrication of catalysts with high catalytic activity by combining earth metal oxides with noble bimetal materials.

Author contributions

Haiyang Wang and Zongcheng Miao conceived the idea and directed the experiments. Wenyuan Duan fabricated all the samples. Ruiyin Zhang, Hao Ma, and Cheng Ma conducted the characterizations. Miaomiao Liang and Yuzhen Zhao analyzed the data. Haiyang Wang and Wenyuan Duan drafted the manuscript. All the authors discussed the results and reviewed the manuscript.

Conflicts of interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this work.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (Grant No. 52173263), the Regional Innovation Capability Guidance Program of Shaanxi (No. 2022QFY03-02), the Natural Science Foundation of Anhui Province, China (No. 2108085J11), Natural Science Basic Research Plan in Shaanxi Province of China (Program No. 2022JQ-533), the Scientific Research Program Funded by Shaanxi Provincial Education Department (No. 22JK0595, 22JK0590, 22JK0592, 22JP100), the Fundamental Research Funds for the Central Universities, Northwestern Polytechnical University (No. D5000210825), the Scientific research fund for high-level talents of Xijing University (No. XJ21B17) and the Youth Innovation Team of Shaanxi Universities.

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Footnotes

† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d2ra07395a

‡ These authors contributed equally to this work.

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