Effect of calcination temperature on the low-temperature oxidation of CO over CoOx/TiO2 catalysts

A 5 wt% CoOx/TiO2 catalyst has been used to study the effect of calcination temperature on the activity of this catalyst for CO oxidation at 100 °C under a net oxidizing condition in a continuous flow type fixed-bed reactor system, and the catalyst samples have been characterized using TPD, XPS and XRD measurements. The catalyst after calcination at 450 °C gave highest activity for this low-temperature CO oxidation, and XPS measurements yielded that a 780.2-eV Co 2p3/2 main peak appeared with this catalyst sample and this binding energy was similar to that measured with pure Co3O4. After calcination at 570 °C, the catalyst, which had possessed practically no activity in the oxidation reaction, gave a Co 2p3/2 main structure peak at 781.3 eV which was very similar to those obtained for synthesized ConTiOn+2 compounds (CoTiO3 and Co2TiO4), and this catalyst sample had relatively negligible CO chemisorption as observed by TPD spectra. XRD peaks indicating only the formation of Co3O4 particles on titania surface were developed in the catalyst samples after calcination at temperatures ≥350 °C. Based on these characterization results, five types of Co species could be modeled to exist with the catalyst calcined at different temperatures. Among these surface Co species, the Type A clean Co3O4 particles were predominant on a sample of the catalyst after calcination at 450 °C and highly active for CO oxidation at 100 °C, and the calcination at 570 °C gave the Type B Co3O4 particles with complete ConTiOn+2 overlayers inactive for this oxidation reaction.