DFT Studies On The Cu Catalyst For Ethyl Acetate Synthesis From Ethanol Dehydrogenation

Synthesis of ethyl acetate from ethanol is the most promising chemicaltechnology. Cu-based catalysts are the only commercial ones used in ethyl acetateproduction from ethanol. To develop more efficient Cu-based catalysts, the maincatalyst copper should be understood very well and comprehensively. There aremany scientific questions which should be answered for ethanol dehydrogenation toethyl acetate on Cu-based catalysts. For example, the differences of reactionactivities of ethyl acetate synthesis on different Cu surfaces; the size effects of Cuclusters and the hydrogen bond effects on this reaction. Consequently, the DensityFunctional Theoretical (DFT) and experimental method are used to investigate thereaction of ethanol dehydrogenation to ethyl acetate on Cu catalysts in this thesis.The reaction mechanisms for ethanol dehydrogenation to ethyl acetate ondifferent Cu surfaces were investigated by DFT. Comparing with our previouslyresults on Cu(111) surface, the catalytic activities showed great differences in thesethree low-index Cu surfaces. Cu(100) and Cu(110) surfaces showed higher catalyticactivities than Cu(111) surface. The d band center was larger, which was the closer tothe fermi energy, the activation energy of this reaction would be lower.The reaction activities for ethanol dehydrogenation to acetaldehyde on Cu(111),Cu(100) and Cu(110) surfaces were measured by experimental method. The reactionwas much more favorable on Cu(100) and Cu(110) surfaces than on Cu(111) surface,in a good agreement with the DFT results.The ethanol dehydrogenation to ethyl acetate on Cu1atom, Cu2and Cu13clusterswere investigated by DFT method, respectively. Cu13cluster showed better catalyticactivities for each elementary reaction in ethyl acetate synthesis process. However,Cu1atom and Cu2cluster showed different reaction activities for differentelementary reaction.This was due to the values of HOMO-LUMO gap of the systemswere changed as the alteration of the molecular orbitals of the system, when theconcerned species strongly adsorbed on Cu1atom and Cu2cluster. However, thestrongly adsorbed species were hard to change the value of HOMO-LUMO gap forCu13cluster, due to the larger cluster size. For the reaction of ethanoldehydrogenation to ethyl acetate on small Cu clusters, the reaction activities were mainly decided by the value of HOMO-LUMO gap of the system when the specieswere adsorbed on the Cu clusters.The effect of hydrogen bond on the mechanisms of ethanol catalyticdehydrogenation to ethoxy on Cu surfaces was studied by DFT method. It was foundthat the formation of hydrogen bond was a kind of energy favorable process whentwo ethanol moleculars were co-adsorbed on the Cu surface. With formation ofhydrogen bond, the activation energy for dehydrogenation were lowerd by0.13eVand0.05eV on Cu(111) and Cu(110) surfaces, respectively. The activation energyfor dehydrogenation was increased by0.08eV on Cu(100) surfaces. There were twomain factors wo influence the activation energy by hydrogen bond. Firstly, the O-Hbond was weakened due to the electronic re-distribution under the influence ofhydrogen bond; Secondly, the activation energies were changed due to the differenceof the adsorption configuration of ethanol molecular under the influence of hydrogenbond. However, the hydrogen bond could not alter the reaction barriers of ethanoldehydrogenation to ethoxy group on the three kinds of Cu surfaces markedly. Thesurface structures were still the main factor to determine the activity for catalyticdehydrogenation of ethanol to ethyl acetate.