DFT Study On Pd-Au(100) Surface Property And The Catalytic Performance On Vinyl Acetate Synthesis

Vinyl acetate plays an important role in organic raw materials, and it holds asignificant position in the development of national economy. With the globaldevelopment of the petrochemical industry, acetoxylation of ethylene has graduallyreplace the acetylene method and become the dominant commercial route for thesynthesis of VAc with its technology and economy advantage. Pd-Au catalyst systemis adopted by most of the production process, the strengthening and improvement ofthe catalytic performance has been extensively valued by every country. Densityfuntional theory is based on the essence of electronics, which can investigate andexplain the catalytic mechanism in a deep way, thus providing supports for thecatalytic performance enhancement and reaction control of the vinyl acetate synthesis.In this work, the surface properties of the active Pd-Au(100) catalyst arediscussed, the adsorption properties of the key reagents and their elementary reactionson the surface are systematically studied using molecular simulation methods.First, the configuration properties of several Pd-Au(100) alloy surfaces withdifferent Pd surface coverage and atom arrangement are studied. The surfaceconfigurations consisting Pd monomers isolated by Au are found to be energeticallyfavorable than that of large first neighbor Pd sites. The PdsnAu surface has beenselected as the computational model to study the catalytic performance on vinylacetate synthesis, which is more energetically favorable and the surface coverage isquite close to the real highly active catalyst. While PdfnAu, PdislAu with a larger Pdsurface coverage are also chosen as a comparison. The electronic properties of thethree alloy surfaces are systematically studied. The results show that the electronredistribution induced by alloying with Au causes the Pd d band electron distributionbeing more narrower as the number of first-neighbor Pd atoms decreases.Adsorption properties show that ethylene, acetic acid and acetate species arechemically adsorbed on Pd-Au(100) surfaces, whose structures depend on theadsorption sites. The frontier molecular orbitals of the two reagents become closer dueto the adsorption of the Pd-Au(100) surfaces. The HOMO-LUMO-gap in theco-adsorption system becomes larger as the number of the surface first-neighbor Pdatoms increases, making the coupling reaction between ethylene and acetate morefavorable.The coupling of ethylene and acetate, and the dehydrogenation of ethylene on Pd-Au(100) surfaces are further studied. The results show that ethylene tends to reactwith acetate species on surfaces with a lower Pd surface coverage like PdsnAu andPdfnAu, while it is more likely to dehydrogenate on surfaces with a higher Pd surfacecoverage like PdislAu.In conclusion, on the one hand, the surface configurations with a lower Pd surfacecoverage make the coupling of ethylene and acetate more favorable to VAHintermediate in a single step; On the other hand, they can reduce the possibility ofother possible side reactions induced by ethylene dehydrogenation. The study in thispaper reveals the catalytic performance of different Pd-Au(100) surfaceconfigurations on vinyl acetate synthesis.