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

Abstract

Zirconia, titania, titania–alumina and silica–alumina supported and unsupported MnOx catalysts were prepared and characterized by X-ray diffractometry and photoelectron spectroscopy, infrared spectroscopy and nitrogen sorptometry. Their catalytic activities were tested towards total oxidation of carbon monoxide and methane. The results show the unsupported MnOx (exposed on an α-Mn2O3 bulk structure) to catalyze CO oxidation at ⩽250°C and CH4 oxidation at 250°C, and to remain chemically and structurally stable. The CO oxidation activity of MnOx is improved when dispersed on zirconia, whereas its CH4 oxidation activity is improved on silica–alumina. These results may help in concluding that (i) CO oxidation is not the rate determining step of the oxidation of CH4, (ii) availability of strong acid sites (as those exposed on silica–alumina) is important for CH4 oxidation and (iii) the difference in the catalytic activity towards the oxidation of CO and CH4 resides in the need for different catalytic functions for each reaction, which are, therefore, not related in terms of kinetic control.