Studies On Benzyl Alcohol Selective Oxidation Catalyzed By SiO₂-TiO₂ Composite Materials Supported Pt And Cu Catalysts

Benzaldehyde is an important chemical intermediate,widely used in the synthesis of high value-added chemicals in medicine,food,perfume and other fields.Selective oxidation of benzyl alcohol with H₂O₂ and O₂ as oxidants to benzaldehyde is a new green synthesis process,which has attracted extensive attention.One of the cores of the research is the development of high-efficiency catalysts.In the study of supported catalysts for selective oxidation of benzyl alcohol,the regulation of physical and chemical properties of catalyst support materials,the ways of generating metal and metal oxide active centers on the support materials,and the performance of supported metal and metal oxide catalysts for selective oxidation of benzyl alcohol are worthy of in-depth study.In this thesis,SiO₂-TiO₂ composites were synthesized by sol-gel method.It is found that the hydrothermal treatment step of the preparation process is the key step of determining the crystal phase of TiO₂ in SiO₂-TiO₂ composites.By adjusting the preparation parameters,SiO₂-TiO₂ composites with single anatase crystal phase of TiO₂species（AST）and SiO₂-TiO₂ composites with single rutile crystal phase of TiO₂species（RST）were successfully obtained.For the first time,in these two types of SiO₂-TiO₂ composites with different crystal phases of TiO₂ species,similar specific surface area,pore size and similar Si/Tiratio were obtained.Pt and Cu were loaded on the surface of TiO₂ species in AST and RST materials by one-time photodeposition and multiple photodeposition to form Pt~0 particles and copper oxide species,and the supported Pt/SiO₂-TiO₂ catalyst and Cu O_x/SiO₂-TiO₂catalyst were obtained respectively.The controllable adjustment of Pt~0 particle and copper oxide particle size is realized through different photodeposition processes.In the selective oxidation of benzyl alcohol with H₂O₂ as oxidant,it is found that Pt/SiO₂-TiO₂ catalyst can show higher than 90%conversion of benzyl alcohol and maintain more than 99%selectivity of benzaldehyde.The performance of Pt/SiO₂-TiO₂catalyst for selective oxidation of benzyl alcohol exhibits support effects and size effect of Pt particle size,resulting high catalytic performance with smaller Pt particle size.The catalytic activity of Cu O_x/SiO₂-TiO₂ catalyst is lower than that of Pt/SiO₂-TiO₂catalyst,and the selectivity of benzaldehyde is significantly lower than that of Pt/SiO₂-TiO₂ catalyst.The selectivity of Cu O_x/SiO₂-TiO₂ catalyst for benzaldehyde fluctuates in the range of about 35-85%.At the same time,a large amount of salicylaldehyde and a small amount of cresol can be obtained.The selectivity of salicylaldehyde can fluctuate in the range of about 15-60%.The reason why Pt/SiO₂-TiO₂ catalyst and Cu O_x/SiO₂-TiO₂ catalyst show significant difference on product selectivity is that the former cannot produce highly oxidizing hydroxyl radicals,while the latter can produce a large number of hydroxyl radicals.In addition,the product distribution of CuO_x/SiO₂-TiO₂ catalyst also shows a certain support effect.When the particle size of copper species on RST supported catalyst is larger,it is conducive to obtain more salicylaldehyde.Compared with the Cu O_x/AST（MP）catalyst prepared by multiple photodeposition,the CuO_x/AST（P）catalyst prepared by one photodeposition method is easier to obtain benzaldehyde.