DFT Study On Effect Of CO On The System Of Acetoxylation Of Ethylene To Vinyl Acetate

Vinyl acetate (VAc) is an important organic chemical material, which issynthesized by ethylene, acetic acid and oxygen in gas phase. With the problems ofthe worldwide shortage of energy, the growth of oil prices, and environmentalpollution, the process of acetoxylation of bio-ethylene to product VAc has got moreand more attention. The silica supported palladium-gold bimetallic catalyst is appliedin the industrial process of acetoxylation of ethylene to VAc. Due to the cost of Pd-Aucatalyst, more researches about how to increase the activity and prolong the servicelife have been done. Considering that there is carbon monoxide in upper streamproducts-ethylene, which affects the activity of catalyst, so in this paper, DensityFunctional Theory (DFT) was carried out to investigate the thermal stability of PdAualloy, the mono-adsorption properties of ethylene and acetate, and co-adsorption ofreactants with carbon monoxide, which was in order to research the effect of CO onacetoxylation of ethylene to VAc.It was found that the non-continuous ensembles of Pd1, Pdsn and Pds were moreenergy-stable than continuous configurations of Pdnn and Pdc on PdAu(100) andPdAu(111) surfaces, and with the increase of number of continuous Pd atom, thecontinuous configurations were harder to form on surface.The adsorption properties of CO, ethylene and acetate on different ensembles ofPdAu(100) and PdAu(111) surfaces were calculated, and it was shown that CO wasmore stable adsorbed on Pd atom than on Au atom. Due to the effect of interactionbetween Pd and Au on surface, the order of adsorption energy of CO, ethylene andacetate on different ensembles was Pdc>Pdnn>Pd1≈Pdsn≈Pds. The turn of theco-adsorption energy of CO, ethylene and acetate was acetate> CO> ethylene, andthe co-adsorption energy of three adsorbates was smaller than the mono-adsorptionenergy, especially of ethylene. So the adsorption of ethylene was blocked, whichresulted in the decrease of catalyst activity, even leaded to the deactivation of PdAucatalyst.The effect of CO on acetoxylation of ethylene to VAc was reflected in two aspects.First, CO was more stable adsorbed on Pd atom than ethylene. Then the adsorption ofethylene would be blocked, and the catalytic activity of PdAu alloy would decrease. Second, PdAu alloy can also catalyze the CO oxidation reaction. If the content of COwas controlled in a certain extent, CO can be shifted to CO2, which would decreasethe effect of CO on catalytic activity of PdAu alloy.After the investigation of the interaction between Pd and Au of PdAu alloy, andthe mono-adsorption and competitive adsorption properties of CO, ethylene andacetate, the effect of CO on VAc system was analysed in electronic level, whichprovide a theory support for increasing the activity and prolong the life span of Pd-Aucatalyst.