Recent Developments in the Partial Oxidation of Methane to Syngas

Natural gas is catalytically converted into several bulk chemicals such as ammonia, methanol, dimethyl ether, and synthetic liquid fuels by Fischer-Tropsch synthesis and similar processes. The main step in the conversion of natural gas to these products is the production of synthesis gas with the desired composition ranging from H2/CO = 3:1 used for the production of ammonia to the 1:1 mixture preferred for production of dimethyl ether. Catalysts and catalytic processes are important in the production of synthesis gas from natural gas. In this work, relevant catalytic systems employed recently in the production of syngas by the catalytic partial oxidation of methane, as well as experimental evidences on the reaction mechanisms are examined. Differences in methane dissociation, binding site preferences, stability of OH surface species, surface residence times of active species and contributions from lattice oxygen atoms and support species are considered. The methane dissociation requires reduced metal sites, but at elevated temperatures oxides of active species may be reduced by direct interaction with methane or from the reaction with H2 and CO (or C). The comparison of elementary reaction steps on Pt and Rh illustrates the fact that a key factor to produce hydrogen as primary product is a high activation energy barrier to the formation of OH. Another essential property for the formation of H2 and CO as primary products is a low surface coverage of intermediates, such that the probability of O-H, OH-H and CO-O interactions is reduced.