A Study On Adsorption Properties And Deactivation Mechanism Of Zinc Acetate/Activated Carbon Catalyst For Vinyl Acetate Synthesis From Acetylene

As an important organic chemical material,vinyl acetate is widely used in chemical industry.The carbide acetylene method is still the main technology to produce vinyl acetate due to the abundant coal resources in our country.Zinc acetate/activated carbon has been used as the catalyst to produce vinyl acetate from acetylene and the improvement and strengthening of the catalytic performance have attracted great attention.Density functional theory(DFT)has been widely used in the field of catalysis in recent years,and it can explain the catalytic mechanism at the atomic or molecular level based on the essence of electronic properties,thus providing theoretical supports for design and improvement of catalysts.In this work,the adsorption properties of zinc acetate and reactants(acetylene and acetic acid)on zinc acetate/activated carbon surface were studied,and the adsorption of the key reactants and their elementary reactions of vinylacetylene were systematically investigated using DFT method.Firstly,the configurations and electronic properties of zinc acetate loaded on hydroxyl or carboxyl decorated activated carbon(AC)were studied.The adsorption strength of zinc acetate on AC is much weaker than that on OH-AC and COOH-AC,demonstrating that existence of hydroxyl and carboxyl can increase the interaction between zinc acetate and AC and decrease the loss of zinc acetate.Moreover,it is easier for zinc acetate on COOH-AC to activate reactants than that on OH-AC because of a lower molecular orbital gap.Secondly,it is found to be physisorption for acetylene adsorbed on all catalyst surfaces by studying the adsorption properties of reactants related to the formation of VAc from acetylene,and it seems easier for acetylene to be adsorbed on the catalyst when hydroxyl is present compared with carboxyl.For acetic acid,it is adsorbed physically on activated carbon,while it appears to be chemisorption on zinc acetate and zinc acetate/activated carbon.Different from acetylene,it is more ready for acetic acid to be adsorbed on catalyst surface decorated with carboxyl.All above results show that activated carbon can be modified by physical or chemical method to change the distribution of functional groups and increase the adsorption strength of reactants.Finally,the adsorption and co-adsorption properties of species related to the formation of vinylacetylene were studied.By searching for the transition states of elementary reactions,we found that as one of the possible reaction paths,acetylene undergoes dehydrogenation and hydrogenation reaction to produce acetenyl and vinyl,respectively.Then acetenyl tends to react wit h vinyl species to generate vinylacetylene,in which the dehydrogenation of acetylene is found to be the rate-determining step.The other path is CHCH ?CHC*?CHCCHCH*? CH2 CHCCH,in which the dehydrogenation of acetylene is also found to be the rate-determining step.In addition,it occurs easily for the hydrogenation of acetylene to vinyl due to a low barrier of 0.26 eV,demonstrating that the formation of vinyl may be an intermediate reaction for VAc synthesis.