Oxidative coupling of methane catalyzed unexpected synergistic effect of the by rare earth oxides oxide mixtures

Oxidative coupling of methane (OCM) catalyzed by a series of rare earth oxides (REO) and mixtures of REO was studied using a continuous-flow quartz reactor at atmospheric pressure, 650-900 degreesC and variable gas flow rates of methane and air. The mixtures of the rare earth oxides available industrially (as intermediate products in commercial RE metal manufacturing) revealed good efficiency in the OCM. Catalytic performance of the light group of REO consisting of lanthanum, praseodymium, neodymium and cerium oxides with 5.5 wt.% of ceria is comparable to that of the individual oxides (samaria, ytterbia and europia). Addition of 10 wt.% of ceria to pure lanthana unexpectedly enhanced the efficiency of the catalyst. Raman spectroscopy as well as XRD suggested an oxide-oxide interaction between lanthana and ceria providing formation of additional oxygen vacancies. (C) 2002 Elsevier Science B.V. All rights reserved.