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

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 C-2 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%Na2WO4-5%Mn/SiO2, using tetraethoxysilane as the Si precursor) showed the best performance for OCM, with C-2 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. (C) 2013 Elsevier B.V. All rights reserved.