Abstract
The present work addresses the influence of the support on the catalytic behavior of Co(3)O(4)-based catalysts in the combustion of lean methane present in the exhaust gases from natural gas vehicular engines. Three different supports were selected, namely γ-alumina, magnesia and ceria and the corresponding catalysts were loaded with a nominal cobalt content of 30 wt. %. The samples were characterized by N(2) physisorption, wavelength dispersive X-ray fluorescence (WDXRF), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction with hydrogen and methane. The performance was negatively influenced by a strong cobalt-support interaction, which in turn reduced the amount of active cobalt species as Co(3)O(4). Hence, when alumina or magnesia supports were employed, the formation of CoAl(2)O(4) or Co-Mg mixed oxides, respectively, with a low reducibility was evident, while ceria showed a lower affinity for deposited cobalt and this remained essentially as Co(3)O(4). Furthermore, the observed partial insertion of Ce into the Co(3)O(4) lattice played a beneficial role in promoting the oxygen mobility at low temperatures and consequently the catalytic activity. This catalyst also exhibited a good thermal stability while the presence of water vapor in the feedstream induced a partial inhibition, which was found to be completely reversible.