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

• Solution combustion synthesis is promising for preparing OCM catalysts.
• The Na2WO4-Mn/SiO2 catalyst is optimized by adding different metals and Si precursors.
• The optimum catalyst exhibits 27% C2 yield at ethylene/ethane ratio 3.6.
• The reaction kinetics are well described by a previously proposed reaction scheme.

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%Na2WO4–5%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.

Parity plot for methane conversion rate and product formation rates, in μmol/g s.Figure optionsDownload high-quality image (71 K)Download as PowerPoint slide