Au nanoparticles supported on Ce-Zr oxides catalysts were prepared and characterized in order to study the role of support for the oxidative esterification of aldehydes in the presence of molecular oxygen. Ce-Zr solid solutions were synthesized by using (NH 4 ) 2 Ce(NO 3 ) 6 as precursor, while the mixed oxides were obtained by Ce(NO 3 ) 3 precursor. The solid solutions exhibited smaller crystallite size, higher BET surface area, and larger amount of H 2 consumption, acidity and basicity than the mixed oxides at the same Ce/Zr 10 mole ratio due to the incorporation of Zr 4+ into ceria lattice. The effect of the support was investigated owing to all samples presenting the similar Au particle size confirmed by HAADF-STEM study. Supports with higher reducibility showed better performances by activation of methanol to methoxy and facilitating the β-H elimination of hemiacetal. We also found that the formation of hemiacetal was enhanced by acidic sites and basic sites of Au catalysts supported on solid solutions possessing similar reducibility. 15 Plausible reaction mechanism for oxidative esterification of aldehydes on Ce-Zr solid solution supported Au nanoparticles was proposed. The screening catalyst was also applicable to the oxidative esterification of different benzyl aldehydes with high yields. The catalyst could be reused after a simple separation for eight times keeping high selectivity above 99%. 65 the screening catalyst have also been investigated.
Esterification is one of the most pivotal organic transformations. Au catalysts were prepared by using a colloid deposition method with poly(vinyl alcohol) (PVA) as a protective agent. The catalyst was used for the oxidative esterification of methacrylate (MAL) to methyl methacrylate (MMA). Three pre‐treatments were used to remove the PVA, which is unfavorable for catalytic activity. It is found that the catalyst pre‐treated at 300 °C showed substantially improved activity owing to the lower PVA loading compared with catalysts treated with hot water washing and water reflux. Surprisingly, it is also found that the distribution and loading content of Au particles was closely related to the pH of the colloid solution. We demonstrate that the deposition process is controlled by the different charge of the support surface at different colloid solution pH. Further, the catalysts with similar size Au particles loaded on TiO2, SiO2, Al2O3, CeO2, ZrO2, and ZnO were successfully prepared by controlling the colloid solution pH. The Au/ZnO catalyst presented the best performance, which may be a result of the strong basic surface sites that improved the formation of the intermediate and the strong interaction between Au and ZnO. This interaction caused an anchoring effect and changed the geometries of Au particles, which could enhance the stability of catalysts and promote the mobility of oxygen, respectively.
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