Gongde Wu

Increasing methane emissions exacerbate global warming and drive an urgent demand for efficient low-temperature catalytic combustion. Double perovskite oxides are promising due to tunable compositions and abundant active sites, but their intrinsic activity is limited by the pristine perovskite framework. Herein, we combine A-site cation deficiency engineering with noble metal loading to modulate oxygen vacancies and Pd species on double perovskites for methane combustion. A series of A-site deficient La2-xNiCoO6 (x = 0, 0.1, 0.2) double perovskites were prepared by sol–gel, followed by deposition–precipitation loading of 1 wt% Pd to obtain Pd/La2-xNiCoO6 catalysts. Moderate A-site deficiency coupled with Pd introduction significantly enhances methane combustion. Pd/La1.9NiCoO6 delivered the best performance, with T90 (temperature for 90% conversion) = 462 °C and Ea = 60.7 kJ/mol. Multiple characterizations reveal that moderate A-site deficiency preserves the perovskite framework, generates more oxygen vacancies than pristine La2NiCoO6, and increases Co3+ and Ni3+ proportions. The defective support effectively anchors and disperses Pd, yielding a higher Pd2+/Pd4+ ratio. Furthermore, these oxygen vacancies interact synergistically with highly dispersed Pd through Pd–O–B (B = Co, Ni) interfacial sites, facilitating charge redistribution, accelerating gaseous oxygen activation and lattice oxygen migration, and generating rich surface-active oxygen species conducive to methane combustion. This work provides theoretical and experimental insights for designing high-performance low-temperature methane combustion catalysts.

Water impurities are ubiquitous in industrial processes, derived from crude feedstocks and petrochemical by-products. Water exhibits preferential adsorption over ethyl acetate at Cu+ active sites, creating competitive occupation and greatly restricting the practical application of Cu-based catalysts for ethyl acetate hydrogenation. Nevertheless, viable approaches to improve the water resistance of Cu/SiO2 catalysts through modulating the interfacial electronic characteristics of Cu+ sites are still lacking. A series of Cu/SiO2 catalysts with different copper loadings were synthesized via an ammonia evaporation-hydrothermal method. Multiple characterizations were applied to probe structural evolution, electronic behavior of Cu+ sites, and structure-activity relationships under reaction conditions containing water. Copper loading can tailor the interfacial interaction and electron transfer between copper species and SiO2 support. Increased Cu loading weakens interfacial electron migration, enhances d-orbital localization of Cu+, reduces active site positive charge, and weakens water adsorption. Meanwhile, high Cu loading greatly increases surface Cu+ content. Benefiting from this synergy, Cu40 achieves outstanding low-temperature activity and water resistance, challenging the conventional view that high Cu dispersion dominates catalytic performance. This work clarifies the mechanism of Cu–O–Si interfacial electronic regulation and provides a feasible route for developing high-efficiency water-resistant hydrogenation catalysts.

The green synthesis of propylene carbonate (PC) via urea transesterification with propylene glycol has been severely hindered by the unsatisfactory PC selectivity and the leaching of active sites using zinc-based solid catalysts. In this context, several metal cations (Mx+, M= Ca, Mg, Fe, Al, Zn, x= 2 or 3) were incorporated into SiO2 support by the co-precipitation method to obtain M2Ox-SiO2 catalysts with varieties of acidic-basic characters. In view of the adverse effect of secondary reactions on the selectivity of the target product of PC, M2Ox-SiO2 oxides were employed to catalyze all the identified reaction paths to better clarify the function of acidic-basic pairs. The conversion of urea to the intermediate 2-hydroxypropyl carbamate (2-HPC) can be readily achieved irrespective of the catalyst's acidic-basic nature, whereas the transformation of 2-HPC into PC requires a catalytic material with a dominance of basic sites. However, further investigation revealed that basic sites could exacerbate the occurrence of side-reactions too, which were significantly disadvantage for the formation of PC. Fortunately, a remarkable catalytic performance could be realized over MgO-SiO2 catalyst possessing a well-suitable amounts of basic site. Additionally, it could be readily recycled without a notable decline in activity towards the PC synthesis. Finally, three green metrics such as environmental factor, process mass intensity and atom uitlization were evaluated to validate the environmental and economic compatibility of the PC production from urea and PG over the model catalyst.

The green synthesis of propylene carbonate (PC) via urea transesterification with propylene glycol has been severely hindered by the unsatisfactory PC selectivity and the leaching of active sites using zinc-based solid catalysts. In this context, several metal cations (Mx+, M= Ca, Mg, Fe, Al, Zn, x= 2 or 3) were incorporated into SiO2 support by the co-precipitation method to obtain M2Ox-SiO2 catalysts with varieties of acidic-basic characters. In view of the adverse effect of secondary reactions on the selectivity of the target product of PC, M2Ox-SiO2 oxides were employed to catalyze all the identified reaction paths to better clarify the function of acidic-basic pairs. The conversion of urea to the intermediate 2-hydroxypropyl carbamate (2-HPC) can be readily achieved irrespective of the catalyst's acidic-basic nature, whereas the transformation of 2-HPC into PC requires a catalytic material with a dominance of basic sites. However, further investigation revealed that basic sites could exacerbate the occurrence of side-reactions too, which were significantly disadvantage for the formation of PC. Fortunately, a remarkable catalytic performance could be realized over MgO-SiO2 catalyst possessing a well-suitable amounts of basic site. Additionally, it could be readily recycled without a notable decline in activity towards the PC synthesis. Finally, three green metrics such as environmental factor, process mass intensity and atom uitlization were evaluated to validate the environmental and economic compatibility of the PC production from urea and PG over the model catalyst.

Catalytic oxidation technology provides a clean approach for the abatement of low-concentration methane (CH4), yet developing efficient non-noble metal catalysts remains a key challenge. In this work, we design a high-performance CeNiO3-based catalyst through a green mechanochemical ball-milling strategy combined with subsequent impregnation of Co3O4 nanoparticles, realizing both defect engineering and heterostructure construction. The optimized 0.4Co3O4/BM-CeNiO3 catalyst exhibits remarkable CH4 combustion activity with a T90 (temperature at 90% CH4 conversion) of 478 °C, approximately 100 °C lower than pure CeNiO3. It also shows good stability and tolerable water resistance under 10 vol.% water vapor. Characterization results and DFT calculations confirmed that the ball-milling-induced defects and oxygen vacancies (Ov) enriched active sites and optimized oxygen migration, whereas the heterojunction synergistically strengthened CH4 adsorption and weakened H2O adsorption, thus simultaneously boosting activity and water tolerance. In-situ DRIFTS verified that CH4 oxidation followed the Mars-van Krevelen (MvK) mechanism with formate and carbonate as key intermediates. This work provides a facile and green approach for designing highly active, stable, and water-resistant non-noble metal catalysts for CH4 combustion.

5Cu-USY and Ce-doped 5Cu8Ce-USY zeolite catalysts were prepared by the conventional impregnation method. The obtained catalysts were subjected to the hydrothermal ageing process. The catalytic performance of the selective catalytic reduction of NO_x with NH₃ (NH₃-SCR) was evaluated on both fresh and aged catalysts. Physical/chemical characterizations such as X-ray diffraction (XRD), H₂ temperature-programmed reduction (H₂-TPR), and X-ray photoelectron spectroscopy (XPS) were performed, along with detailed in situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) experiments including CO adsorption, NH₃ adsorption, and NO + O₂ reactions. Results showed that, for the 5Cu-USY catalyst, hydrothermal ageing treatment could somehow improve the low-temperature SCR activity, but it also led to significant formation of unfavorable byproducts NO₂ and N₂O. Such an activity change can be attributed to hydrothermal ageing inducing the migration of isolated Cu⁺ species in the sodalite cavities towards the super cages of the USY zeolites. The increased content of Cu⁺ species in the super cages was beneficial for the low-temperature activity improvement, but, at the same time, it also facilitated ammonia oxidation at high temperatures. Ce doping after hydrothermal ageing has a “double-edged sword” effect on the catalytic performance. First of all, Ce doping can inhibit Cu species migration by self-occupying the internal cage sites; thus, the catalytic performance of 5Cu8Ce-USY-700H remains stable after ageing. Secondly, Ce doping introduces a CuO_x–CeO₂ strong interaction, which facilitates lattice oxygen mobility by forming more oxygen vacancies so as to increase the concentration of surface active oxygen. These changes, on the one hand, could help to promote further oxidative decomposition of nitrate/nitrite intermediates and improve the catalytic performance. But, on the other hand, it also causes the byproduct generation to become more severe.

A series of supported MnO_x/MgAl-layered double hydroxide (LDH) catalysts were prepared by hydrothermal co-precipitation to investigate their catalytic performances for low-temperature formaldehyde oxidation reactions. Activity tests show that the 10Mn/Mg₃Al₁-LDH catalyst exhibits higher efficiency for low-temperature formaldehyde oxidation with a high CO₂ yield. It also shows remarkable long-term operational stability as well as good adaptability to different velocities and humidities. Various characterizations were carried out to establish the possible structure–activity correlations. The results show that there were a large number of hydroxyl groups in the 10Mn/MgAl-LDH catalysts, and the hydroxyl groups were positively correlated with Mg²⁺ content. The outstanding catalytic performance of 10Mn/Mg₃Al₁-LDH can be attributed to abundant surface hydroxyl groups, surface adsorbed oxygen and higher Mn⁴⁺/Mn³⁺ ratios. Through in situ Fourier-transform infrared spectroscopy (in situ FTIR), it was revealed that formaldehyde was gradually converted into CO₂ and water with dioxymethylene (DOM), formate and carbonate as the major intermediates under the action of both active oxygen and active hydroxyl groups. The active oxygen and active hydroxyl groups consumed in the process are continuously replenished by the effective reaction between the oxygen molecules in the air and the active site of the catalyst. The low-temperature asynchronous conversion of formaldehyde results in the accumulation of some intermediates on the catalyst surface covering the active center, which induces catalyst deactivation.