Bulk Versus Surface Modification of Alumina with Mn and Ce Based Oxides for CH(4) Catalytic Combustion

This study presents the synthesis and characterization of lanthanum-modified alumina supported cerium–manganese mixed oxides, which were prepared by three different methods (coprecipitation, impregnation and citrate-based sol-gel method) followed by calcination at 500 °C. The physicochemical properties of the synthesized materials were investigated by various characterization techniques, namely: nitrogen adsorption-desorption isotherms, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and H(2)–temperature programmed reduction (TPR). This experimental study demonstrated that the role of the catalytic surface is much more important than the bulk one. Indeed, the incipient impregnation of CeO(2)–MnO(x) catalyst, supported on an optimized amount of 4 wt.% La(2)O(3)–Al(2)O(3,) provided the best results of the catalytic combustion of methane on our catalytic micro-convertors. This is mainly due to: (i) the highest pore size dimensions according to the Brunauer-Emmett-Teller (BET) investigations, (ii) the highest amount of Mn(4+) or/and Ce(4+) on the surface as revealed by XPS, (iii) the presence of a mixed phase (Ce(2)MnO(6)) as shown by X-ray diffraction; and (iv) a higher reducibility of Mn(4+) or/and Ce(4+) species as displayed by H(2)–TPR and therefore more reactive oxygen species.