Efficient methane to ethane conversion via C–H bond activation catalyzed by a MOF-derived porous PdO/TiO₂ nanocomposite

Abstract

The photocatalytic conversion of methane (CH₄) into high-value multicarbon (C₂₊) products under ambient conditions provides a highly promising approach for the transformation of the energy structure and environmental protection. However, the high C–H bond dissociation energy of CH₄ and the overoxidation of methyl radical (˙CH₃) intermediates greatly limit the conversion of CH₄ to C₂₊ products. Herein, we demonstrate a metal–organic framework (MOF) crystal engineering strategy to synthesize a MOF-derived PdO/TiO₂ nanocomposite for photocatalytic nonoxidative coupling of methane (NOCM), achieving high selectivity and activity in the conversion of CH₄ to ethane (C₂H₆). Mechanistic investigations reveal that the spatially separated active sites for C–H bond cleavage and C–C coupling contribute to the efficient conversion of CH₄ to C₂H₆. Specifically, the lattice oxygen captures the photogenerated holes, leading to the formation of oxygen radical anions (˙O⁻), which activate the C–H bond and generate ˙CH₃ intermediates. PdO stabilizes ˙CH₃ intermediates, effectively inhibiting the overoxidation of ˙CH₃, and thereby promoting the C–C coupling process. This work opens a new avenue for the rational design of efficient MOF-derived photocatalysts for NOCM.

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New concepts

Methane (CH₄), the primary component of natural gas and one of the most abundant fossil energy sources, holds immense potential as a feedstock for producing high-value hydrocarbons. However, current industrial routes for methane transformation are highly energy-intensive, largely stemming from the high C–H bond energy and low polarizability of CH₄. Herein, we report the design of a porous PdO/TiO₂ nanocomposite through a MOF crystal engineering strategy for highly efficient and selective photocatalytic methane to ethane (C₂H₆). The optimal PdO/TiO₂ photocatalyst achieves a C₂H₆ yield of 1196 μmol g⁻¹ h⁻¹ with a selectivity of 94%, outperforming most of the previously reported works on photocatalytic NOCM. Mechanistic investigations reveal that the spatially separated active sites (C–H cleavage on TiO₂ and C–C coupling on PdO) contribute to the efficient conversion of CH₄ to C₂H₆. This study provides a novel and efficient approach for CH₄ conversion under mild conditions, highlighting the potential of MOF-derived photocatalysts in NOCM applications.

1. Introduction

Methane (CH₄) is the primary component of natural gas and one of the most abundant fossil energy sources.¹ With the growing global energy demand and the ongoing energy transition, upgrading CH₄ into high-value products and easily transportable fuels has become a current research focus.^2,3 Among the various CH₄ conversion methods, nonoxidative coupling of methane (NOCM) has garnered considerable research interest as a direct route to convert CH₄ into higher-value hydrocarbons.⁴ However, due to the high C–H bond energy and low polarizability of CH₄, NOCM faces significant thermodynamic limitations. Initiating NOCM via thermocatalysis demands high temperatures (>650 °C), resulting in severe coke deposition and catalyst deactivation.⁵ Under such circumstances, photoredox catalysis emerges as a promising alternative for NOCM, enabling NOCM to occur under ambient conditions.^6,7

The photocatalytic NOCM reaction involves multiple steps, including C–H activation, hydrogen (H) abstraction, and C–C coupling.⁸ These processes are closely linked to electron transfer, the redox reaction of photogenerated charges and the adsorption–desorption of reaction intermediates or products in the reaction on catalysts.⁹ However, previous NOCM studies typically rely on single metal sites to control the C–H bond activation and the C–C coupling, which inevitably limits the efficiency of CH₄ conversion.¹⁰ To overcome these limitations, the rational design of photocatalysts with multiple active sites to facilitate both C–H activation and C–C coupling is crucial for improving the CH₄ conversion efficiency.^11,12 Metal–organic frameworks (MOFs), an emerging class of porous materials, have gained significant attention due to their well-defined and customizable structures, making them ideal for incorporating diverse active sites.¹³ Using a MOF as a precursor, the derived nanomaterials not only retain pre-designed structures but also exhibit enhanced photogenerated carrier separation performance,¹⁴ thereby promoting CH₄ adsorption and activation. Moreover, the unique coordination environment provided by the MOF structure can further optimize the distribution and stability of the active sites,¹⁵ which can effectively ensure the stability of methyl (˙CH₃) intermediates to facilitate C–C coupling.

Herein, we report the design of a porous PdO/TiO₂ nanocomposite through a MOF crystal engineering strategy for highly efficient and selective photocatalytic NOCM. The optimal PdO/TiO₂ photocatalyst achieves a C₂H₆ yield of 1196 μmol g⁻¹ h⁻¹ with a selectivity of 94%, outperforming most of the previously reported works on photocatalytic NOCM. Mechanistic investigations reveal that the spatially separated active sites for C–H cleavage and C–C coupling contribute to the efficient conversion of CH₄ to C₂H₆. Electron paramagnetic resonance (EPR) spectra demonstrate that oxygen radical anions (˙O⁻) produced by photoexcitation promote the activation of the C–H bond of CH₄ to form the ˙CH₃ intermediates. PdO improves the adsorption of ˙CH₃, effectively suppressing the overoxidation of ˙CH₃ intermediates and lattice oxygen, and facilitating the C–C coupling process. This study provides a novel and efficient approach for CH₄ conversion under mild conditions, highlighting the potential of MOF-derived photocatalysts in NOCM applications.

2. Results and discussion

The PdO/TiO₂ nanocomposite was fabricated via a MOF crystal engineering strategy, as depicted in Fig. 1a. Ti-BPDC is grown from 2,2′-bipyridine-5,5′-dicarboxylic acid (BPDC) and Ti(OC₂H₅)₄ (TET) through a simple solvothermal method,^16,17 with Pd uniformly dispersed within Ti-BPDC via coordination binding, forming Ti-BPDC-Pd. X-ray diffraction (XRD) patterns of Ti-BPDC-Pd demonstrate the well-maintained MOF crystallinity (Fig. S1, SI). Scanning electron microscopy (SEM) images indicate the sheet-like morphology of Ti-BPDC-Pd similar to the pristine MOF (Fig. S2, SI). Subsequently, the PdO/TiO₂ was obtained through controlled pyrolysis at 400 °C (Fig. S3a and b, SI). As shown in Fig. 1b, the PdO/TiO₂ consists of stacked nanosheets. Transmission electron microscopy (TEM) (Fig. S4, SI) of PdO/TiO₂ shows that the PdO is homogeneously distributed on the surface of TiO₂, and high-resolution TEM (HRTEM) images reveal the (101) lattice fringes of anatase TiO₂ and the (002) lattice fringes of PdO (Fig. 1c and d).^18,19 Elemental mapping images (Fig. 1e) indicate the presence of Ti, O, and Pd in PdO/TiO₂, further confirming the uniform distribution of PdO on the surface of TiO₂.

Fig. 1 (a) Schematic illustration of the synthesis of the PdO/TiO₂ nanocomposite. C, N, O, H, Ti and Pd atoms are colored in dark, dark-blue, red, light-blue, purple and yellow, respectively. (b) SEM image of PdO/TiO₂. (c) TEM image and (d) HRTEM image of PdO/TiO₂. (e) High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image and elemental mapping results of PdO/TiO₂.

X-ray photoelectron spectroscopy (XPS) has been applied to determine the surface electronic state of the elements. The survey spectra (Fig. S5, SI), together with the high-resolution XPS spectra (Fig. 2a–c) of the PdO/TiO₂ composites, confirm the presence of all elements (Pd, O, and Ti) associated with PdO and TiO₂, which aligns well with the results of element mapping. The Pd 3d XPS spectrum is presented in Fig. 2a, and the peaks of 336.49 eV and 341.79 eV for PdO/TiO₂ are attributed to Pd 3d_5/2 and Pd 3d_3/2 of Pd²⁺, respectively.^20,21Fig. 2b displays the Ti 2p XPS spectra of the samples, where the peaks of 458.59 eV and 464.06 eV for TiO₂ are ascribed to Ti⁴⁺.²² Furthermore, the peak observed at 458.04 eV is attributed to Ti³⁺, whose presence is typically accompanied by the formation of oxygen vacancies.²³ In the O 1s XPS spectra shown in Fig. 2c, the sharp peak of 529.74 eV and the broad peak of 530.79 eV are assigned to lattice oxygen and surface-adsorbed oxygen.²⁴ Notably, the characteristic peaks of Ti 2p and O 1s in PdO/TiO₂ shift to higher binding energies after PdO modification, indicating the transfer of electrons from TiO₂ to PdO.²⁵

Fig. 2 (a) High-resolution XPS spectrum of Pd 3d of PdO/TiO₂. (b) and (c) High-resolution XPS spectra of Ti 2p and O 1s of PdO/TiO₂ and TiO₂. (d) XRD patterns of PdO/TiO₂ and TiO₂. (e) Nitrogen adsorption–desorption isotherms of PdO/TiO₂ (inset: pore size distribution of PdO/TiO₂). (f) EPR spectra of PdO/TiO₂ and TiO₂.

The XRD patterns (Fig. 2d) reveal that all samples exhibit peaks at 2θ values of 25.8°, 37.8°, and 48.0°, corresponding to the (101), (004), and (200) crystallographic planes of tetragonal anatase TiO₂ (PDF# 21-1272). Additionally, the peak appearing at 33.6° in the PdO/TiO₂ corresponds to the (002) crystallographic plane of PdO (PDF# 75-0584), indicating that PdO has a certain degree of crystallinity on the TiO₂ surface; however, due to the low content or high dispersion of PdO, signals from other crystallographic planes are not detected.¹⁸ Nitrogen adsorption–desorption isotherms, shown in Fig. 2e and Fig. S6 (SI), demonstrate that the samples exhibit type IV isotherms with H3 hysteresis loops, indicating the presence of an irregular mesoporous structure.^26,27 The specific surface area, pore size, and pore volume are detailed in Table S1 (SI). PdO/TiO₂ exhibits a well-developed mesoporous structure with a large surface area (240.1 m² g⁻¹), which is beneficial for CH₄ adsorption.²⁸

Electron paramagnetic resonance (EPR) spectra (Fig. 2f) indicate a signal peak at g = 2.003 belonging to the oxygen vacancy,²⁹ which is consistent with the XPS results. The introduction of PdO alters the local electronic structure of TiO₂, facilitating electron transfer from TiO₂ to PdO, which stabilizes Ti³⁺ species and promotes the formation of oxygen vacancies to maintain charge neutrality.³⁰ Moreover, Ultraviolet-visible (UV-Vis) diffuse reflectance spectroscopy (DRS) has been used to measure the properties of optical absorption of the samples. As shown in Fig. S7a (SI), pristine TiO₂ exhibits weak light absorption. In contrast, the modification with PdO significantly enhances the light absorption intensity of TiO₂, which may be due to the interfacial interaction between PdO and TiO₂.³¹ Moreover, on the basis of Tauc plots of (αhν)²versus photo energy (hν),³² the band gap energy (E_g) of TiO₂ is derived to be 3.3 eV (Fig. S7b, SI).

Upon obtaining the structural information of the catalysts, we then conducted a systematic evaluation of the photocatalytic activity of TiO₂ and PdO/TiO₂ for NOCM. As shown in Fig. 3a, blank TiO₂ exhibits a low C₂H₆ production rate (233 μmol g⁻¹ h⁻¹). After PdO modification, the C₂H₆ production rate of the PdO/TiO₂ composite significantly increased, with a normal distribution trend observed in relation to varying PdO content (Table S2, SI). Notably, the 1PdO/TiO₂ sample shows the optimal photocatalytic performance, with a C₂H₆ production rate increased to 565 μmol g⁻¹ h⁻¹. In addition, the MOF precursor (Ti-BPDC-Pd) was also evaluated under identical conditions and displayed negligible C₂H₆ formation (Fig. S8, SI). Considering the exceptional performance of noble metals such as Au and Pt in NOCM reaction,^33,34 we prepared a series of TiO₂ samples modified with the same proportion (1%) of different metals using the same method, and compared their photocatalytic activities for NOCM (Fig. S9, SI). As is seen clearly in Fig. S10 (SI), PdO/TiO₂ demonstrates the highest C₂H₆ production rate among them. Additionally, we investigated the performance of other oxide supports (P25, ZnO, Al₂O₃ and CeO₂) in place of TiO₂ under the same reaction conditions (Fig. S11, SI). The results indicate that PdO/TiO₂ exhibits a significantly higher C₂H₆ production rate than PdO/P25, PdO/Al₂O₃, PdO/ZnO, and PdO/CeO₂ (Fig. 3b), suggesting that MOF-derived TiO₂ is a highly promising support for NOCM reaction. Further analysis reveals a positive correlation between the photocatalytic activity of PdO/TiO₂ and light intensity, whose C₂H₆ production rate can reach 1196 μmol g⁻¹ h⁻¹ at a light intensity of 300 mW cm⁻² with a selectivity of 94% (Fig. S12 and S13, SI). The apparent quantum yield (AQY) for the NOCM reaction was also evaluated. The PdO/TiO₂ catalyst exhibited an AQY of 1.1% under 360 nm monochromatic light irradiation. Under AM 1.5G simulated sunlight, the AQY decreased to 0.26%, which is significantly lower than that under monochromatic illumination. This reduction can be attributed to the fact that the catalyst mainly absorbs ultraviolet light, resulting in limited utilization of the visible-light portion of the solar spectrum.

Fig. 3 (a) Photocatalytic NOCM performance over PdO/TiO₂ with different contents of PdO after 4 h of illumination. (b) Photocatalytic NOCM performance over PdO-supported oxide substrates. (c) Time-dependent photocatalytic C₂H₆ production over PdO/TiO₂ and TiO₂. (d) Photocatalytic cycling stability test for the PdO/TiO₂ (each cycle lasts 4 h). (e) Mass spectrum of C₂H₆ produced over PdO/TiO₂ using ¹³CH₄ as the reactant. (f) Comparison of the activity and selectivity with other catalysts for NOCM.

The C₂H₆ yield of all samples increases and then stabilizes over time (Fig. 3c), and PdO/TiO₂ reaches a C₂H₆ production of 701.5 μmol g⁻¹ in the first hour, but the rate gradually decreases due to the consumption of lattice oxygen.⁸ This phenomenon is also further observed in the cycling experiment. As shown in Fig. S14 (SI), the photocatalytic activity of PdO/TiO₂ decreases slightly with the increase of the cycle period. However, by heat treatment in air, the lattice oxygen on PdO/TiO₂ is replenished, and the catalytic activity is successfully restored to its original level in subsequent cycles (Fig. 3d).¹⁰ To further investigate whether the decline in activity during cycling is associated with changes in the Pd oxidation state, XPS analysis was performed on the PdO/TiO₂ catalyst after reaction. As shown in the Pd 3d spectra (Fig. S15, SI), the binding energies remain at 336.24 eV and 341.51 eV, which are characteristic of Pd²⁺. These results confirm that the valence state of Pd remains unchanged after the reaction. Therefore, the observed decrease in activity is more likely due to the temporary depletion of lattice oxygen, rather than changes in the Pd electronic structure. Furthermore, no CH₄-derived products are detected for control experiments conducted in the absence of reactant, photocatalyst, or light irradiation (Fig. S16, SI), confirming that this is a light-driven process and CH₄ is the sole source of carbon. Isotopic labelling tests using ¹³CH₄ as the feedstock further confirm the origin of the resulting C₂H₆. As shown in Fig. 3e, dominant peaks ascribed to ¹³C₂H₆ and its molecular fragments can be observed (28 = ¹³C₂H₂, 29 = ¹³C₂H₃, 30 = ¹³C₂H₄, 31 = ¹³C₂H₅).³⁵ These results collectively confirm that the generated C₂H₆ originates solely from the feedstock CH₄. By virtue of the high activity and selectivity of C₂H₆, our optimal PdO/TiO₂ catalyst demonstrates a competitive performance in NOCM compared to other recently reported alternatives (Fig. 3f, details are listed in Table S3, SI).

The photocatalytic NOCM primarily involves CH₄ adsorption, C–H bond activation, and subsequent C–C coupling.⁶ To figure out the functional orientation of each part of PdO/TiO₂ in photocatalytic NOCM, CH₄ temperature-programmed-desorption (TPD) was performed to investigate the adsorption of CH₄ on the samples. As disclosed in Fig. 4a, TiO₂ exhibits two distinct desorption peaks at 211 °C and 379 °C, with the more intense peak appearing at 211 °C, indicating its strong adsorption capacity for CH₄ at low temperatures. This enhanced adsorption performance can be ascribed to the well-developed mesoporous structure of MOF-derived TiO₂, which provides abundant surface area and accessible channels for CH₄ molecules. In contrast, the PdO/TiO₂ composite displays a single dominant desorption peak at 251 °C with a notably reduced overall desorption intensity, suggesting a reduced CH₄ adsorption capacity. This decrease is likely attributable to the PdO loading, which reduces the specific surface area and induces partial collapse of the pore structure, thereby hindering CH₄ adsorption. Furthermore, the electrochemical impedance spectroscopy (EIS) and transient photocurrent response spectra (Fig. S17a and b, SI) show that the modification of PdO significantly improves the photogenerated charge separation efficiency. To gain deeper insight into the charge transfer process, in situ XPS measurements were conducted. As illustrated in Fig. 4b and c, upon light irradiation, the Pd 3d spectrogram shows clear peak splitting, with a peak at 343 eV, indicating that it has undergone partial reduction due to the gain of electrons. Concurrently, the O 1s peak shifts positively by 0.28 eV, implying that photogenerated holes tend to accumulate at the oxygen sites of TiO₂ for CH₄ activation.³⁴In situ EPR measurements of the samples further support this conclusion. As disclosed in Fig. 4d, under an Ar atmosphere and dark conditions, no signal peak is detected. Upon light irradiation, the newly appeared signal peaks at g_x = 2.031 and g_y = 2.002 are attributed to ˙O⁻ generated by surface lattice oxygen through capturing photogenerated holes.³⁶ When CH₄ was subsequently introduced into the EPR chamber, the intensity of the ˙O⁻ clearly lowered, demonstrating that the ˙O⁻ reacted with CH₄.³⁷ It is noteworthy that the similar changes observed in the EPR spectra of PdO/TiO₂ and TiO₂ suggest that CH₄ activation primarily occurs on the surface of TiO₂. Additionally, due to the electron-rich nature of the oxygen vacancies (O_v),³⁸ O_v may be a favorable position for CH₄ adsorption by promoting the formation of ˙O⁻ on adjacent lattice oxygen sites to activate the C–H bond. To gain insight into the intermediates of photocatalytic NOCM on PdO/TiO₂, under liquid-phase reaction conditions, EPR measurements were carried out using 5,5′-dimethyl-1-pyrroline N-oxide (DMPO) as a radical scavenger to further investigate the potential intermediates. As shown in Fig. 4e, distinct characteristic signals of ˙CH₃ and ˙OH are detected on PdO/TiO₂. Given that ˙OH originates from the water in the test conditions,^39,40 this finding indicates that the surface ˙CH₃ is the key intermediate for CH₄ coupling.⁴¹ In comparison, the ˙CH₃ signal on the surface of TiO₂ was weak, suggesting the high efficiency of CH₄ dissociation on PdO/TiO₂.

Fig. 4 (a) CH₄-TPD profiles of PdO/TiO₂ and TiO₂. In situ XPS spectra for (b) Pd 3d and (c) O 1s of PdO/TiO₂ under the dark condition and light irradiation. (d) In situ EPR spectra in Ar or CH₄ atmosphere over the PdO/TiO₂ and TiO₂. (e) In situ EPR spectra of the samples in water with CH₄ dissolved under light irradiation (EPR measurement is performed to investigate possible radicals by using DMPO as a radical scavenger. In order to detect the radicals, the reaction needs to be carried out in water with CH₄ as the filling gas under light irradiation). (f) In situ FTIR spectra of photocatalytic NOCM over PdO/TiO₂. (g) Proposed photocatalytic mechanism of the NOCM reaction over PdO/TiO₂.

To elucidate the detailed reaction mechanism underlying the photocatalytic NOCM, we employed an in situ Fourier transform infrared spectroscopy (FTIR) approach to track the dynamic evolution of surface-adsorbed species and key intermediates during the reaction. During the dark adsorption phase, characteristic peaks of C–H deformation vibration of CH₄ appear around 1300 cm⁻¹ as well as 3000 cm⁻¹ (Fig. S18, SI).⁴² As shown in Fig. 4f, under light irradiation, a new peak around 1558 cm⁻¹ is assigned to the C–H symmetry vibration of adsorbed CH₄.⁴³ Simultaneously, the ˙CH₃ deformation vibration mode observed at 1469 cm⁻¹ confirms that CH₄ undergoes rapid dissociation by photogenerated charge carriers on the PdO/TiO₂ surface.¹⁰ Additionally, the peak at 3528 cm⁻¹ is attributed to the stretching and bending vibrations of the O–H bonds of H₂O, indicating that the H atoms from CH₄ dissociation combine with lattice oxygen to form H₂O.⁸ Meanwhile, the slight growth of C=O (1671 cm⁻¹) stretching vibrational modes is assigned to the species for CO₂ formation, suggesting the sluggish overoxidation of CH₄ on PdO/TiO₂. In contrast, an intense C=O stretching vibration signal can be observed for TiO₂ (Fig. S19, SI). Taken as a whole, the modification with PdO enhances the separation efficiency of photogenerated electron–hole pairs, thus promoting the dissociation of CH₄ on the TiO₂ surface. Additionally, PdO effectively stabilizes the ˙CH₃ intermediates and diminishes the overoxidation of CH₄ under light irradiation, facilitating the C–C coupling process to produce C₂H₆.

Based on the experimental findings, we propose a mechanistic pathway for the photocatalytic NOCM process over PdO/TiO₂, as illustrated in Fig. 4g. Under photoexcitation, PdO/TiO₂ nanocomposites generate electron–hole pairs, CH₄ molecules are adsorbed at the O_v site, and the photogenerated holes interact with the nearby lattice oxygen, resulting in the formation of oxygen radical anions (˙O⁻). These radicals extract hydrogen from the C–H bond, initiating CH₄ activation and producing the ˙CH₃ intermediate.⁴⁴ The PdO component plays a dual role by capturing and stabilizing ˙CH₃ radicals, thus preventing their overoxidation and facilitating C–C coupling to form C₂H₆. Meanwhile, the photo-generated electrons participate in the reaction between the H atoms produced by the dissociation of CH₄ and the lattice oxygen, generating H₂O as a by-product. This cooperative interaction between TiO₂ and PdO ensures efficient charge separation and controlled radical transformation, ultimately enabling the selective photocatalytic conversion of CH₄ to C₂H₆ under mild conditions.⁴⁵

3. Conclusions

In conclusion, we have synthesized PdO/TiO₂via a MOF crystal engineering strategy for photocatalytic NOCM, achieving a C₂H₆ yield of 1196 μmol g⁻¹ h⁻¹ with a selectivity of 94%, which is superior to most of the recent works on NOCM. Mechanistic investigations reveal that the MOF-derived TiO₂ provides enhanced CH₄ adsorption capacity due to its porous structure, while the spatial separation of active sites for C–H bond activation and C–C coupling significantly improves the CH₄–C₂H₆ conversion efficiency. Additionally, PdO modification not only improves the photogenerated carrier separation efficiency, but also prevents the overoxidation of ˙CH₃ intermediates and lattice oxygen, therefore driving the C–C coupling process. This work highlights the importance of catalytic site engineering for reaction regulation, offering new insights into the design of efficient photocatalysts for NOCM under mild conditions.

Conflicts of interest

There are no conflicts to declare.

Data availability

The data supporting this article have been included within the article and supplementary information (SI). Supplementary information: additional experimental preparation schemes, material characterization data and photoactivity results. See DOI: https://doi.org/10.1039/d5nh00636h.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (22572017, 22472032, 22172030, and 22072023), the Research Fund for Outstanding Talents at University of Electronic Science and Technology of China (A1098531023601522), the Program for National Science and Technology Innovation Leading Talents (00387072), the China Postdoctoral Science Foundation (2023M740513), the China National Postdoctoral Program for Innovative Talents (BX20240055), and the Jiangxi Province “Double Thousand Plan” (No. jxsq2023102143).

Notes and references

1. X. Y. Li, C. Wang and J. W. Tang, Nat. Rev. Mater., 2022, 7, 617–632.
2. P. Wang, R. Shi, J. Q. Zhao and T. R. Zhang, Adv. Sci., 2023, 11, 2305471.
3. Y. H. Jiang, S. Y. Li, Y. Y. Fan and Z. Y. Tang, Angew. Chem., Int. Ed., 2024, 63, e202404658.
4. G. M. Wang, X. W. Mu, J. Y. Li, Q. Y. Zhan, Y. M. Qian, X. Y. Mu and L. Li, Angew. Chem., Int. Ed., 2021, 60, 20760–20764.
5. N. F. Dummer, D. J. Willock, Q. He, M. J. Howard, R. J. Lewis, G. D. Qi, S. H. Taylor, J. Xu, D. Bethell, C. J. Kiely and G. J. Hutchings, Chem. Rev., 2022, 123, 6359–6411.
6. Y.-F. Wang, M.-Y. Qi, M. Conte, Z.-R. Tang and Y.-J. Xu, Angew. Chem., Int. Ed., 2024, 63, e202407791.
7. K. Lin, F. Xiao, Y. Xie, K. Pan, L. Wang, W. Zhou and H. G. Fu, Nanoscale Horiz., 2020, 5, 1596–1602.
8. J. J. Zhang, J. N. Shen, D. M. Li, J. L. Long, X. C. Gao, W. H. Feng, S. Y. Zhang, Z. Z. Zhang, X. X. Wang and W. M. Yang, ACS Catal., 2023, 13, 2904.
9. M.-Y. Qi, M. Conte, M. Anpo, Z.-R. Tang and Y.-J. Xu, Chem. Rev., 2021, 121, 13051–13085.
10. W. B. Jiang, J. X. Low, K. K. Mao, D. L. Duan, S. M. Chen, W. Liu, C. W. Pao, J. Ma, S. K. Sang, C. Shu, X. Y. Zhan, Z. M. Qi, H. Zhang, Z. Liu, X. J. Wu, R. Long, L. Song and Y. J. Xiong, J. Am. Chem. Soc., 2020, 143, 269–278.
11. G. Y. Zhai, L. J. Cai, J. Ma, Y. H. Chen, Z. H. Liu, S. H. Si, D. L. Duan, S. K. Sang, J. W. Li, X. Y. Wang, Y. A. Liu, B. Qian, C. Y. Liu, Y. Pan, N. Zhang, D. Liu, R. Long and Y. J. Xiong, Sci. Adv., 2024, 10, eado4390.
12. J. Ma, J. X. Low, D. Wu, W. B. Gong, H. J. Chen, D. Liu, R. Long and Y. J. Xiong, Nanoscale Horiz., 2022, 8, 63–68.
13. X.-Y. Lin, M.-Y. Qi, Z.-R. Tang and Y.-J. Xu, Appl. Catal., B, 2022, 315, 121708.
14. N. Y. Huang, B. Li, D. J. Wu, Z. Y. Chen, B. Shao, D. Chen, Y. T. Zheng, W. J. Wang, C. Z. Yang, M. Gu, L. Li and Q. Xu, Angew. Chem., Int. Ed., 2024, 63, e202319177.
15. J. B. Qin, Y. B. Dou, J. C. Zhou, V. M. Candelario, H. R. Andersen, C. Hélix-Nielsen and W. J. Zhang, Adv. Funct. Mater., 2023, 2214839.
16. X. Y. He, Y. J. Ding, Z. N. Huang, M. Liu, M. F. Chi, Z. L. Wu, C. Segre, C. S. Song, X. Wang and X. W. Guo, Angew. Chem., Int. Ed., 2023, 62, e202217439.
17. X. Y. He, X. T. Gao, X. Chen, S. Hu, F. C. Tan, Y. J. Xiong, R. Long, M. Liu, E. Tse, F. Wei, H. Yang, J. G. Hou, C. S. Song and X. W. Guo, Appl. Catal., B, 2023, 327, 122418.
18. Z.-S. Huang, Y.-F. Wang, M.-Y. Qi, M. Conte, Z.-R. Tang and Y.-J. Xu, Angew. Chem., Int. Ed., 2024, 63, e202412707.
19. T. J. Wang, F. M. Li, H. Huang, S. W. Yin, P. Chen, P. J. Jin and Y. Chen, Adv. Funct. Mater., 2020, 30, 2000534.
20. Y.-F. Wang, M.-Y. Qi, M. Conte, Z.-R. Tang and Y.-J. Xu, Angew. Chem., Int. Ed., 2023, 62, e202304306.
21. M.-Q. Yang and Y.-J. Xu, Nanoscale Horiz., 2016, 1, 185–200.
22. M.-Y. Qi, Q. Lin, Z.-R. Tang and Y.-J. Xu, Appl. Catal., B, 2022, 307, 121158.
23. M. C. Guo, Q. Q. Meng, M.-L. Gao, L. R. Zheng, Q. X. Li, L. Jiao and H.-L. Jiang, Angew. Chem., Int. Ed., 2024, 64, e202418964.
24. S. D. Wang, B. Q. Ge, Z. X. Yang, H. W. Zhang, Q. Yang, C. J. Hu, X. J. Bao and P. Yuan, ACS Catal., 2024, 14, 1432–1442.
25. L.-X. Zhang, Z.-R. Tang, M.-Y. Qi and Y.-J. Xu, J. Mater. Chem. A, 2024, 12, 19029–19038.
26. X. Chen, X. Chen, S. C. Cai, J. Chen, W. J. Xu, H. P. Jia and J. Chen, Chem. Eng. J., 2017, 334, 768–779.
27. N. Kim, J. S. Nam, J. Jo, J. Seong, H. Kim, Y. Kwon, M. S. Lah, J. H. Lee, T.-H. Kwon and J. Ryu, Nanoscale Horiz., 2021, 6, 379–385.
28. Q. Li, Y.-X. Gao, M. Zhang, H. Gao, J. Chen and H. P. Jia, Appl. Catal., B, 2021, 303, 120905.
29. P. Zhang, J. W. Li, H. W. Huang, X. Y. Sui, H. H. Zeng, H. J. Lu, Y. Wang, Y. Y. Jia, J. A. Steele, Y. H. Ao, M. B. J. Roeffaers, S. Dai, Z. Z. Zhang, L. Z. Wang, X. Z. Fu and J. L. Long, J. Am. Chem. Soc., 2024, 146, 24150–24157.
30. C. Y. Wang, Y. B. Li, C. B. Zhang, X. Y. Chen, C. L. Liu, W. Z. Weng, W. P. Shan and H. He, Appl. Catal., B, 2020, 282, 119540.
31. H. Wang, Z. M. Wang, Z. Z. Zhang, Y. M. Fan, X. Z. Fu and W. X. Dai, Fuel, 2024, 362, 130865.
32. M. Y. Li, X. Liu, Y. Che, H. Z. Xing, F. F. Sun, W. Zhou and G. S. Zhu, Angew. Chem., Int. Ed., 2023, 62, e202308651.
33. S. Song, H. Song, L. M. Li, S. Y. Wang, W. Chu, K. Peng, X. G. Meng, Q. Wang, B. W. Deng, Q. X. Liu, Z. Wang, Y. X. Weng, H. L. Hu, H. W. Lin, T. Kako and J. H. Ye, Nat. Catal., 2021, 4, 1032–1042.
34. S. Q. Wu, X. J. Tan, J. Y. Lei, H. J. Chen, L. Z. Wang and J. L. Zhang, J. Am. Chem. Soc., 2019, 141, 6592–6600.
35. X. Y. Li, C. Wang, J. L. Yang, X. Wu, Y. X. Xu, Y. Yang, J. G. Yu, J. Delgado, N. Martsinovich, X. Sun, X. S. Zheng, W. X. Huang and J. W. Tang, Nat. Commun., 2023, 14, 6343.
36. P. Wang, R. Shi, Y. X. Zhao, Z. H. Li, J. Q. Zhao, J. Q. Zhao, G. I. N. Waterhouse, L. Z. Wu and T. R. Zhang, Angew. Chem., Int. Ed., 2023, 62, e20230431.
37. X. G. Meng, X. J. Cui, N. P. Rajan, L. Yu, D. H. Deng and X. H. Bao, Chem, 2019, 5, 2296–2325.
38. Q. Li, Y. X. Gao, M. Zhang, H. Gao, J. Chen and H. P. Jia, Appl. Catal., B, 2021, 303, 120905.
39. H. Sato, A. Ishikawa, H. Saito, T. Higashi, K. Takeyasu and T. Sugimoto, Commun. Chem., 2023, 6, 8.
40. K. Takanabe and E. Iglesia, Angew. Chem., Int. Ed., 2008, 47, 7689–7693.
41. W. Q. Zhang, C. F. Fu, J. X. Low, D. L. Duan, J. Ma, W. B. Jiang, Y. H. Chen, H. J. Liu, Z. M. Qi, R. Long, Y. F. Yao, X. B. Li, H. Zhang, Z. Liu, J. L. Yang, Z. G. Zou and Y. J. Xiong, Nat. Commun., 2022, 13, 2806.
42. Y. D. Liu, Y. H. Chen, W. B. Jiang, T. T. Kong, P. H. C. Camargo, C. Gao and Y. J. Xiong, Research, 2022, 2022, 9831340.
43. C. Li and Q. Xin, J. Phys. Chem. C, 1992, 96, 7714–7718.
44. X. W. Zhao, Y. Cao, M. J. Lei, Z. L. Jin and N. Tsubaki, Acta Phys.-Chim. Sin., 2025, 41, 100152.
45. Z. Y. Zhou and Z. L. Jin, Chin. J. Catal., 2025, 74, 294–307.

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