Oxidation of lean methane over cobalt catalysts supported on ceria/alumina

Cobalt (30 %wt.) oxide catalysts supported over ceria-modified (3-18 %wt.) alumina supports were examined for the combustion of lean methane. The prepared samples were characterised by wavelength dispersive X-ray fluorescence, N-2 physisorption, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, temperature-programmed reduction with hydrogen and temperature-programmed reaction with methane. A significant enhancement of the activity was evidenced with respect to the catalyst supported over bare alumina, with an optimal cerium loading of 12 %wt. and a resultant T-50, value of 480 degrees C. The ceria modification was found to induce a dual positive effect on the performance of the cobalt catalysts. On one hand, it acted as a physical barrier between deposited cobalt and alumina, thus inhibiting the cobalt-alumina interaction and the subsequent cobalt aluminate formation. On the other hand, the insertion of cerium ions in the spinel lattice led to a distortion of the structure that in turn resulted in an enhanced mobility of the oxygen species. The optimised catalyst exhibited a relatively good thermal stability for prolonged reaction time intervals (150 h) under dry conditions. The presence of water vapour markedly affected the catalytic performance although this negative effect was partially reversible.