Comparative Kinetic Monte Carlo Study of Acetic Acid Decomposition to Surface Carbon Species and Undesirable Byproducts on Pd(100) and Pd/Au(100) from Density Functional Theory-Based Calculations

摘要

Acetic acid decomposition on Pd(100) and Pd/Au(100) during vinyl acetate (VA) synthesis from ethylene acetoxylation is the primary source of such undesirable byproducts as methanol (CH3OH), acetaldehyde (CH3CHO), ketene (CH2CO), acetone (CH3COCH3), and methane (CH4), and also one possible source of surface carbon formation, which will lead to the deactivation of the catalyst. In this work, density functional theory (DFT) calculations and kinetic Monte Carlo (kMC) simulation were performed to probe the mechanism of acetic acid decomposition on Pd(100) and Pd/Au(100) at the molecular level. The corresponding adsorption of relevant species involved in acetic acid decomposition on Pd(100) and Pd/Au(100) was investigated, and the transition states of the elementary reactions involved were identified. The results show that the most probable pathway of acetic acid decomposition on Pd/Au(100) is CH3COOH - CH3COO+H - CO2+CH3+H - CO2+CH4, followed by CH3COOH - CH3COO+H - CO2+CH3+H - CO2+CH2+2H - CO2+CH+3H - CO2+C+4H, which agrees nicely with the results of many other researchers that CO2, CH4, H-2 and surface carbon are the main products of acetic acid decomposition. If researchers can find some way to suppress the decarboxylation of CH3COO at the beginning in the future, then the overall undesirable byproducts can be further greatly reduced, which can significantly improve the quality of VA. Our work can provide guidance for designing and developing novel catalysts with high efficiency for VA synthesis from ethylene acetoxylation.