Oxidation of residual methane from VNG vehicles over Co3O4-based catalysts: Comparison among bulk, Al2O3-supported and Ce-doped catalysts

Cobalt oxide based catalysts with three different active phase configurations, namely bulk, alumina supported and cerium-doped Co3O4 samples were examined for the complete oxidation of methane under conditions similar to those found in the exhaust of VNG engines. The structural and redox properties of the resulting catalysts were determined by N-2 adsorption-desorption, WDXRF, ICP-AES, X-Ray diffraction, temperature-programmed reactions, UV-vis-NIR DRS, XPS and Raman spectroscopy. Alumina-supported catalysts (10-40%wt. Co) were found to be less active, since the strong interactions between the alumina and the Co3O4 active phase were highly detrimental for the redox properties of these catalysts. On the other hand, doping with cerium (10%wt.) led to an increased inherent activity of the Co3O4 phase by distorting the spinel lattice, which resulted in improved structural and redox properties and enhanced mobility of the oxygen species within the spinel lattice. These catalysts were also stable over a prolonged period of time under both dry and humid conditions (150 h).