Revealing the reaction mechanism and kinetic properties for dimethyl maleate hydrogenation on the Cu-Cr catalysts combined DFT with kMC analysis

Abstract

1,4-Butanediol (BDO) is a fine chemical raw material that plays a significant role in the production of degradable plastics. The hydrogenation of dimethyl maleate (HDMM) to BDO is a highly favored technology the industry for its low-cost catalysts and high selectivity. However, the kinetics equation and optimal conditions for HDMM process to BDO on copper-chromium catalysts are still unclear, which has hindered the development of the design of advanced industrial reactors and production processes. Herein, the Cu-Cr(111) surface model was constructed by combining DFT and kMC to investigate the reaction network of the HDMM process. The analysis of the activation barrier and Bader charge revealed that Cu⁰ and Cr act as the active centers for ester hydrogenation and alcohol hydroxyl cleavage, respectively. The dominant pathways and key intermediates for the formation of γ-butyrolactone (GBL), BDO, and tetrahydrofuran (THF) were claimed by TOF and coverage analysis. Changes in the rate-determining step with temperature for BDO formation were observed by the concepts of degree of rate control. Based on the reaction network, a method was proposed to construct the intrinsic kinetic equation models, which are subjected to nonlinear optimization and linear/nonlinear fitting to obtain relevant parameters. Analysis of the kinetic and thermodynamic properties of reactions in the HDMM process revealed that the higher temperature and total pressure, the lower H₂-ester ratio, the higher reaction rates, and different products have different responses to the reaction conditions. Optimal conditions were determined to target different products. This study attempted to span from the microscale to mesoscale, providing theoretical support for novel reactor design for the HDMM process and possibilities for studying the kinetic properties of C₄₊ complex reaction systems through multi-scale simulation.