Generation mechanism of methyl acetate during gas-phase synthesis of vinyl acetate from ethylene on PdAu(100) surface: A combined DFT and kMC study

Methyl acetate is a byproduct that is difficult to completely remove in the gas-phase process of producing vinyl acetate from ethylene. High-quality vinyl acetate products require stringent control of the methyl acetate content. However, studies on the mechanism of methyl acetate formation have not been reported, which constrains the modification of catalysts to reduce its formation. This paper presents a comprehensive study on the generation mechanism of methyl acetate during the ethylene-based vinyl acetate synthesis process over PdAu catalysts, utilizing a combination of DFT (Density Functional Theory) and kMC (kinetic Monte Carlo) simulations. The reaction network for the formation of methyl acetate on PdAu catalysts was constructed. Initially, DFT calculations were employed to investigate the adsorption properties of relevant species on the PdAu(100) surface. The results indicate that surface species preferentially adsorb at the Pd-Au bridge sites, diagonal Pd-Pd hollows, and diagonal Pd-Au hollows on the PdAu(100) catalyst, with a stronger interaction between the Pd atoms and the adsorbed species. Subsequently, DFT calculations were performed to identify the optimal pathways for the generation of methyl acetate on PdAu(100). Based on the kinetic parameters obtained from DFT calculations, kMC simulations were conducted to stimulate the generation process of methyl acetate. The results demonstrate that the dominant pathway for the formation of methyl acetate during the ethylene-based vinyl acetate synthesis over PdAu(100) is through CH2CH2*+O*→CH2CH*+H*→CH3CH*→CH3*+CH*(CH*+H*→CH2*+H*→CH3*)→CH3*+CH3COO*→CH3COOCH3*. The reaction between CH3COO* and CH3* to form methyl acetate is identified as the rate-determining step, with an energy barrier of 1.75 eV and an exothermic reaction heat of −0.53 eV.