Oxidative coupling of methane using catalysts synthesized by solution combustion method: Catalyst optimization and kinetic studies

Abstract The Na₂WO₄-Mn/SiO₂ catalyst has shown promise for oxidative coupling of methane (OCM). Our prior work demonstrates that 10%Na₂WO₄-5%Mn/SiO₂ prepared by solution combustion synthesis (SCS) exhibits good performance in terms of C₂ yield and ethylene to ethane ratio. In this work, we use SCS for preparation of several modified Na₂WO₄-Mn/SiO₂ catalysts for OCM. The catalyst composition was optimized by addition of different metals and Si precursor used. The optimized catalyst (5%La-10%Na ₂WO₄-5%Mn/SiO₂, using tetraethoxysilane as the Si precursor) showed the best performance for OCM, with C₂ yield 27% and ethylene/ethane ratio 3.6 under optimized operating conditions, both values are among the highest reported in the literature. Kinetic studies for this catalyst indicated that methane conversion was first-order in methane and half-order in oxygen, implying that methane activation is likely to be rate-limiting and oxygen adsorption is dissociative. The formation rates of primary products (C₂H₆, CO and CO₂) could be well described by the reaction scheme proposed in a prior work.