Improved Homogeneous-Heterogeneous Kinetic Mechanism Using a Langmuir-Hinshelwood-Based Microkinetic Model for High-Pressure Oxidative Coupling of Methane

A comprehensive microkinetic mechanism for the oxidative coupling of methane (OCM) was developed by using the model La2O3-CeO2 catalyst at industrially relevant conditions up to 0.9 MPa and a gas hourly space velocity (GHSV) of similar to 650,000 h(-1). A Langmuir-Hinshelwood (LH)-based surface mechanism was coupled with gas-phase reactions (KAM 1-GS mechanism). The developed model was verified against low-pressure experimental results that minimized reaction exotherms. The improved LH mechanism, dividing the adsorption steps and surface reactions, provides flexible temperature and pressure dependencies to reproduce the experimental results across broad pressure conditions (0.010-0.80 MPa CH4). Specifically, the adsorption constant of C2H4 was found 20 times larger than that of C2H6 due to the p-electron-related high affinity of C2H4 to the surface. Additionally, high-pressure conditions were well described by considering the non-isothermal behavior from OCM reactions and heat dissipation from the reactor. The rate of production (ROP) results indicated that the enhanced unselective gas-phase reaction at high pressures caused the loss of C2-3 yield.