CO and CH4 total oxidation over manganese oxide supported on ZrO2, TiO2,TiO2-Al2O3 and SiO2-Al2O3 catalysts

Zirconia, titania, titania-alumina and silica-alumina supported and unsuppo rted MnOx catalysts were prepared and characterized by X-ray diffractometry and photoelectron spectroscopy, infrared spectroscopy and nitrogen sorptom etry. Their catalytic activities were tested towards total oxidation of car bon monoxide and methane. The results show the unsupported MnOx (exposed on an alpha-Mn2O3 bulk structure) to catalyze CO oxidation at less than or eq ual to 250 degrees C and CH4 oxidation at greater than or equal to 250 degr ees C, and to remain chemically and structurally stable. The CO oxidation a ctivity of MnOx is improved when dispersed on zirconia, whereas its CH4 oxi dation activity is improved on silica-alumina. These results may help in co ncluding that (i) CO oxidation is not the rate determining step of the oxid ation of CH4, (ii) availability of strong acid sites las those exposed on s ilica-alumina) is important for CH4 oxidation and (iii) the difference in t he catalytic activity towards the oxidation of CO and CH4 resides in the ne ed for different catalytic functions for each reaction, which are, therefor e, not related in terms of kinetic control.