Manganese/Cobalt Oxides Catalyzed Molecular Oxygen Selective Oxidation Of Benzyl Alcohol To Benzaldehyde And Its Reaction Mechanism

The problems of large pollution and high energy consumption in the traditionally industrialized benzyl alcohol-to-benzaldehyde process have not been solved.Meanwhile,precious metal catalysts such as Pt and Au are difficult to be widely applied due to their high cost.Therefore,using transition metal oxides with low cost and good oxidation-reduction ability as catalysts,the green route to synthesize benzaldehyde using molecular oxygen as an oxidant has received extensive attention.To this end,based on MnO₂,Co₃O₄ and LaMn_1-xCo_xO₃ oxide catalysts,this paper carried out work through SBA-n（n=3,15,16）template by modifying,doping,and other methods to explore the metal oxidation of cobalt and manganese.In order to provide technical solutions and theoretical basis for the green industrial route of benzyl alcohol to benzaldehyde in the future.The main experimental research is divided into three parts:（1）Using SBA-n-type mesoporous silica as a template,Co₃O₄ with different pore structure types was prepared,and its catalytic activity of catalyzing the oxidation of benzyl alcohol to benzaldehyde by molecular oxygen was tested,and it was found that when the SBA-16 was used as a template,the prepared Co₃O₄-16 catalyst showed the best catalytic activity:at a reaction temperature of 100℃ and a reaction time of 3 h,the conversion of benzyl alcohol and the selectivity of benzaldehyde were both as high as more than 97%,and the activity order was Co₃O₄-16>Co₃O₄-13>Co₃O₄-dd>Co₃O₄-15.This is because Co₃O₄-16 has the lowest Co³⁺/Co²⁺ratio and the most oxygen vacancies,which is more favorable for the activation of molecular oxygen.（2）Further research found thatα-MnO₂ exhibited better catalytic activity than Co₃O₄ in the catalytic oxidation of benzyl alcohol to benzaldehyde by molecular oxygen.The mesoporousα-MnO₂-n catalyst prepared with SBA-n（n=3,15,16）as a template.The conversion of benzyl alcohol at 30℃ for 3 h can reach 98.5%,94.4%,97.8%.This is because MnO₂ has good oxidation-reduction ability,and the pore-forming agent greatly increases its specific surface area and increases the number of surface oxygen vacancies.At the same time,we compared the catalytic activities of different crystal structure typesα-MnO₂,β-MnO₂,δ-MnO₂ and OMS-2 and studied the oxidation performance ofα-MnO₂ to different types of alcohols.It was found that this type of catalyst has excellent activity for aromatic alcohols,but relatively poor activity for linear alcohols.（3）Based on the above results,LaMn_1-xCo_xO₃ type perovskite oxides were constructed with higher structural stability to further explore their catalytic performance on the production of benzyl alcohol to benzaldehyde by molecular oxygen oxidation.The activity test results show that LaMn_0.95Co_0.05O₃ exhibits the best reactivity:100%conversion and97.3%selectivity can be achieved in 1 h at 70℃.However,many reactants/products will be adsorbed on the surface of this type of catalyst after the reaction,which makes its cyclic reaction performance poor.It needs to be calcined at a certain temperature to restore its activity better.