Chromia on Anatase: A Catalyst for Selective Hydrocarbon Combustion in the Presence of CO

The catalytic activity and selectivity for propane combustion in the presence of CO have been studied with anatase, rutile, eskolaite, chromia-impregnated anatase, and titania-impregnated chromia and its physical mixtures. It was found that the selectivity and activity depend on the TiO2 modification. Cr-doped anatase converts 80 % propane with 100 % selectivity, whereas chromia on rutile converts CO preferentially to propane. Cr10@HOM 500/4 (HOM=Hombikat) and the physical mixture Cr10+HOM 500/4 are promising new catalysts for selective propane oxidation. High-resolution TEM and powder XRD analyses have shown that a solid solution of chromia in anatase is the active phase of these selective oxidation catalysts. Diffuse reflectance UV/Vis spectroscopy demonstrated the effects of Cr-doping of TiO2, and Rietveld refinement analysis implied a solid solution of Cr3+ ions in anatase. Evidence for a Mars–van Krevelen mechanism was obtained. Catalyst deactivation was reduced by increasing the oxygen content in the feed. The catalyst is reactivated by treatment with oxygen.