Insight Into Reaction Mechanism Of Dimethyl Oxalate Hydrogenation To Methyl Glycolate From First Principles

Methyl glycolate(MG)has drawn an increasing attention in the chemical industry owing to its unique chemical and physical properties.Partial hydrogenation of dimethyl oxalate(DMO)has become a more economical and eco-friendly route for the efficient MG synthesis.However,failure to develop catalysts with superior catalytic performance prohibits its commercialization.It is well known that the key to develop catalysts with excellent performance is to understand the reaction mechanism of DMO hydrogenation to MG.In this work,density function theory(DFT)calculations have been performed to investigate the reaction mechanism of DMO hydrogenation to MG on Ag-,Ru-,Cu-,and Ni-based catalysts.Calculated results indicate that the reaction pathways of DMO hydrogenation on these surfaces are as follow:DMO molecules are first adsorbed on the surface and dissociated into acyl species and methoxyl species.The hydrogen atoms generated by hydrogen dissociation then attack the C and O atoms of the acyl species successively and form reaction intermediates,which finally combine with another hydrogen atom to produce MG.Unlike the reaction pathways,the adsorption state of reactants and rate-determining step are absolutely distinct on different catalysts.DMO molecules and hydrogen are dissocatively adsorbed on Ag catalysts while they are adsorbed on Cu-based in a non-dissociative state.On Ru and Ni catalysts,DMO molecules are adsorbed dissociatively while hydrogen are adsorbed in a non-dissociative state.The dissociation of reactants is the rate-determining step on Ag-based catalysts while the hydrogenation of reactive intermediates is the rate-determining step on Ru-,Cu-,and Ni-based catalysts.In addition,the active sites of Cu-based catalyst are also identified.The results suggest that when there are both Cu+ species and Cu0 species on the Cu-based catalysts,the former is responsible for the conversion of reactants while the latter is responsible for the selective hydrogenation to MG.However,when there is only Cu0 species on the Cu-based catalyst surface,it still has the ability to catalyze the reaction.