An in-depth simulation analysis of the reaction mechanism of ethanol dehydration to ethylene and carbon deposition on the γ-Al2O3(100) surface†

Abstract

Ethylene serves as a pivotal chemical commodity, often regarded as a barometer of a nation's petrochemical industry sophistication. The conversion of biomass-derived ethanol into ethylene through dehydration represents an avenue ripe with developmental potential and expansive application horizons. While current research has delved extensively into the primary reaction mechanisms of ethanol dehydration to ethylene facilitated by γ-Al₂O₃ catalysts, the exploration of by-product formation mechanisms remains somewhat superficial and incomplete. In this study, we employ a synergistic approach, harnessing density functional theory (DFT) and kinetic Monte Carlo (kMC) simulations, to scrutinize both the primary and ancillary reaction pathways in the ethanol-to-ethylene dehydration process on the γ-Al₂O₃(100) surface. Our investigation aims to elucidate the optimal production routes for both the main and by-products, while also assessing the impact of reaction conditions on the reaction mechanisms and the carbon deposition phenomenon. Employing DFT, this study concentrates on by-products including ether, hydrogen, methane, carbon monoxide, carbon dioxide, ethane, butene, and water. We have computed the surface adsorption characteristics of the pertinent species and probed into the generation mechanisms of each by-product, thereby ascertaining the most favorable pathways for their formation. Subsequently, kMC simulations were conducted to scrutinize the influence of temperature on the production mechanism of the primary product, ethylene. It was observed that a temperature below 380 °C is detrimental to ethylene formation, wherein a minor quantity of ethylene is predominantly yielded through the intermolecular dehydration of ethanol to form ether, followed by bond scission. Conversely, at temperatures surpassing 380 °C, there is a marked escalation in ethylene production, with the intramolecular dehydration of ethanol to produce ethylene emerging as the predominant route. Furthermore, the study also delved into the impact of reaction conditions on the carbon accumulation process on the catalyst surface. A significant rise in carbon deposition was noted when temperatures exceeded 440 °C. The incorporation of water was found to be advantageous in curbing carbon deposition, with an optimal water-to-ethanol ratio of 3 identified for minimizing coking.