DFT Study On The Mechanism For Catalytic Hydrogenation Of Acetic Acid To Ethanol On Copper-Indium Catalyts

The process of hydrogenation of acetic acid to ethanol based on clean coal utilization can not only meet the growing demand for fuel ethanol,but also alleviate the overcapacity of acetic acid,which has broad development foreground in China.The design and development of non-noble metal catalyst with high activity and excellent selectivity are a hotspot in this research field.In this work,the Density Functional Theory?DFT?method is applied to investigate the hydrogenation of acetic acid to ethanol on the new copper-indium catalyst system.The Cu₂In alloy,In₂O₃ oxide and Cu/In₂O₃ supported catalyst models are constructed.The catalyst properties and reaction mechanisms for acetic acid hydrogenation to ethanol on the three kinds of catalysts are thoroughly and systemically studied.This study aims at providing theoretical guidance for the design and development of new low-cost and high-efficiency non-noble metal industrial catalyst.Firstly,the hydrogenation of acetic acid to ethanol on the Cu₂In?100?alloy surface was studied.By analyzing the reaction energies and activation barriers of the elementary reactions involed in the reaction network,the pathway of CH₃COOH?CH₃COO?CH₃CHOO?CH₃CHO?CH₃CH₂O?CH₃CH₂OH was found to be most favorable.By comparing and analyzing the mechanism of the formation of byproduct ethyl acetate on the surfaces of both Cu₂In?100?and Cu?111?,it was found that the addition of In into Cu catalyst could increase the activation barrier for ethyl acetate formation.The In metal on Cu₂In?100?surface would act as an electron donor,which endow even higher catalytic activity for Cu atoms on the alloy surface.However,the In itself showed rather high chemical inertness on Cu₂In?100?surface,they could isolate the Cu atoms on the alloy surface into small areas,which could effectively inhibit the formation of byproduct ethyl acetate through steric hindrance effect.Secondly,the hydrogenation of acetic acid to ethanol on the oxygen defective In₂O₃?110?surface was studied.The regularity of the formation of six kinds of surface oxygen vacancies on In₂O₃?110?surface under the reaction atmosphere were studied.It was found that the acetic acid in the reaction atmosphere was favorable for the formation of oxygen vacancies on In₂O₃?110?.The mechanism on ethanol synthesis by acetic acid hydrogenation on the two most representative defective In₂O₃?110?surfaces of D1 and D4 surfaces were studied.The easy-to-generate and easy-to-repair properties of oxygen vacancies could promote continuous reactions which was in accordance with the Mars-Van Krevelen mechanism.By comparing the charge distributions and the corresponding elementary reactions on the defective and perfect surfaces,it was found that the formation of oxygen vacancies could leave redundant electrons on the surface,and the oxygen vacancies became potential electron donors.This facilitated the hydrogenation of?-C in CH₃COO*species and the cleavage of C-O bond in CH₃CHOO*species.Finally,the hydrogenation of acetic acid to ethanol on Cu₄/In₂O₃?110?surface was studied.The results showed that hydrogen was mainly enriched on the Cu clusters and the interface between the Cu clusters and In₂O₃,and dissociated at the interface.There exited a synergism effect between Cu clusters and In₂O₃ surface in the process of acetic acid hydrogenation to ethanol on Cu₄/In₂O₃?110?surface.The gaseous hydrogen was dissociated into hydrogen atoms at the Cu clusters,and then spillover hydrogen atoms were continually migrated to acetic acid adsorbed on the oxygen vacancies,and then combined with the intermediates on In₂O₃ surface.The theoretical calculations showed that Cu₄/In₂O₃ showed higher catalytic activity than Cu₂In alloy.Therefore,it was speculated that the Cu/In₂O₃ will be a promising applied catalyst for the hydrogenation of acetic acid to ethanol.