Precious Metal Catalyst In The Liquid Phase Hydrogenation Of Crotonaldehyde Reaction

The selective hydrogenation ofα,β-unsaturated aldehydes to the corresponding unsaturated alcohols is not only of commercial relevance in fine chemical and pharmaceutical intermediate production but also of specific scientific interest.But it remains a great challenge on heterogeneous catalysts due to the thermodynamic and kinetic limitations.Since Au nanoparticles with dimensions usually less than 5 nm are selective for the hydrogenation ofα,β-unsaturated aldehydes to unsaturated alcohols, gold-based catalysts have been extensively studied in this reaction.In present work, gold catalysts prepared from a new method for the selective hydrogenation of crotonaldehyde were investigated.Mesoporous siliceous SBA-15 functionalized byγ-aminopropyltrimethoxysilane (APTMS) was used to immobilize gold nanoparticles.Compared gold catalysts prepared by two different methods,Au_5.0/APTMS-SBA-15 catalyst showed highest actvity and were most selective for crotyl alcohol.To further enhance the selectivity to unsaturated alcohols,promotion of Au catalysts via the addition of indium has been practiced.In liquid phase hydrogenation of crotonaldehyde to crotyl alcohol,on the optimum Au_5.0In_0.75/APTMS-SBA-15 catalyst,the initial selectivity amounts to 78%, and the maximum yield reaches 71%.The high selectivity is originated from the less suppression of the hydrogenation of the C=O bond than that of the C=C bond. Furthermore,the catalyst can be conveniently recovered for reuse without losing of the selectivity.In light of a series of spectroscopic studies,the superior catalytic performance of the Au_5.0In_0.75/APTMS-SBA-15 catalyst is attributed to the electron-donating effects of APTMS and In alloying with Au,favoring more the binding and hydrogenation of the C=O bond of crotonaldehyde.Ag nanoparticles grafted on surface-functionalized mesoporous silica exhibited surprisingly high selectivity and yield to crotyl alcohol,compared with the results from catalysts made with double-solvent method and impregnation method.On Ag/APTMS-SBA-15 catalyst the optimum yield of crotyl alcohol reached 65%and corresponding selectivity reached 70%,which is one of the best results reported in the open literatures dealing with crotonaldehyde over silver catalyst supported on silica. The kinetic study for the hydrogenation of crotonaldehyde over Ag/APTMS-SBA-15 catalyst showed the reaction is zero order with respect to crotonaldehyde and first order with respect to hydrogen at H₂ pressure.The activation energy for this reaction calculated is 57 kJ·mol^-1.The promoting effect of indium on the liquid phase hydrogenation of crotonaldehyde over silver catalyst has been also investigated.On the optimum Ag_9.0In_0.75/SBA-15-ts catalyst,the optimum yield of crotyl alcohol reached 86%and corresponding selectivity reached 87%,which is one of the best results reported in the open literatures dealing with crotonaldehyde over modified silver catalyst supported on silica.