Synthesis Of Nanostructured CeO₂ Materials And Its Application For Catalytic Hydrogenation Of Methyl Benzoate To Benzaldehyde

Benzaldehyde is an important intermediate in the fine chemical industry,such as manufacturing the pharmaceuticals,agrochemicals,perfumes and flavors.The catalytic hydrogenation of benzoic acid or ester to benzaldehyde is a "green" technology,which will be an innovative technology to alternate the current process, i.e.halogenation of aromatic acids followed by hydrolysis,with various drawbacks, such as low yield and production of a large amount of harmful wastes.A large number of metal oxides,including alkali earth oxides,transition metal oxides and rare earth oxides,have been suggested as catalysts for the catalytic hydrogenation of benzoic acid and methyl benzoate.Among these metal oxides catalysts,CeO₂ has shown good performance.However,the conventional bulk CeO₂ generally suffers from a rapid deactivation at relative high temperature in the industrial process.The nanostructured materials possess unique physico-chemical properties have received considerable attention recently,and a lots of methods have been designed to fabricate nanostructued ceria materials.Our works focus on designation and optimization new morphology of nanostructured CeO₂ catalysts,including nanocrystalline CeO₂ materials and nanoporous CeO₂ materials,for the catalytic hydrogenation of methyl benzoate into benzaldehyde.The effects of particle size,morphology and pores on hydrogenation activity are also discussed.1.Size effect of nanocrystalline CeO₂ on activity for hydrogenation of methyl benzoate to benzaldehydeThe oxalate gel precipitation method(OG) and alcohol-water mixture precipitation method(AW) were applied to prepare a series of nanocrystalline CeO₂. Crystal size was successfully controlled by regulation of calcination temperature. Nano-size CeO₂ catalyst was used as catalysts for hydrogenation of methyl benzoate into benzaldehyde,which showed higher activity in a relatively lower temperature compared with the conventional bulk CeO₂.The conversion of methyl benzoate exceeds 90%over CeO₂-AW-400 catalyst at 340℃.The surface area and the concentration of intrinsic oxygen vacancies of the as-prepared catalysts have been investigated as a function of the crystal size.A good correlation was obtained for the catalysts activity with crystal size,which suggested that the significant effect of the crystal size on the reducibility of CeO₂.The present study confirms that large surface area and the concentration of intrinsic oxygen vacancies of the CeO₂ leads to high activity for catalytic hydrogenation of methyl benzoate.Using surface area and the concentration of intrinsic oxygen vacancies as the screening parameters,it is possible to design the new advanced CeO₂ catalysts with high activity for catalytic hydrogenation of methyl benzoate.2.Morphology effect of nanocrystalline CeO₂ on activity for hydrogenation of benzoate into benzaldehyde.Nanocyrstalline CeO₂ with different shapes were synthesized by the hydrothermal method and used as catalysts for catalytic hydrogenation of methyl benzoate into benzaldehyde.Characterization results revealed that the activity of hydrogenation is related not only to the surface area,but also to the shape of the nanosized CeO₂.The CeO₂ nanorods with larger surface area mainly grow along the [110]direction and preferentially expose the more active {100} and {110} faces, which favor the stabilization of intrinsic active oxygen vacancies on the surface of CeO₂,which lead to a higher reducibility of the nanocrystalline CeO₂.The CeO₂ nanorods exhibited the highest activity and perfect stability among the nanocrystalline CeO₂.3.Synthesis of nanoporous CeO₂ catalysts for the hydrogenation of benzoate into benzaldehydeA novel hydrothermal method based on a graft copolymerization reaction between acrylamide and glucose is applied to fabricate nearly monodisperse flowerlike CeO₂ microspheres with marked thermal stability by controlled the reaction time and the calcination procedure,which possesses high surface area and opened 3D hollow hierarchical porous,in view of their potential kinetic advantages. As a catalyst for the hydrogenation of methyl benzoate into benzaldehyde,the mesoporous CeO₂ microspheres show high activity and thermal stability for hydrogenation of methyl benzoate.