Supported oxide catalysts: Cobalt oxide and molydena on titania

Abstract

TiO2 supported MoO3 catalysts were prepared by aqueous impregnation of low area anatase (10 m2g-1) with solutions of (NH4)6Mo7024,4H20 (MT/C series), and H2[Mo03(C204)].H20 (MOT /C series), Three series of CoOx/Ti02 catalysts were fabricated by aqueous impregnation of the same support with solutions of Co(N03)2,6H20 (CT/C series), and Co(CH3COO)2.4H20 (CAT/C series), and by homogeneous precipitation using Co(N03)2,6H20 (CT/HP series), CoO and Mo03 were deposited on Degussa P-25 (55 m2g-1) by aqueous impregnation using (NH4)6Mo7024,4H20 and Co(N03)2,6H20 in three ways: ( i) CoO impregnated first, Mo03 second (CMT series); (ii) Mo03 impregnated first, CoO second (MCT series); and (iii) CoO and Mo03 together (CMTg series). The catalysts were characterized by laser Raman spectroscopy (LRS) , temperature-programmed reduction (TPR) , X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM), Monolayer coverage by XPS was independent of the precursor for the MoOx/Ti02 catalysts, but a function of the method of preparat ion and the precursor for the CoOx /Ti02 catalysts. XPS resul ts for the CMTg series differed from those for the CMT and MCT series, suggesting different surface species had been formed by varying the mode of impregnation, Phase diagrams relating semiquantitatively to the oxide contents are presented. 2-propanol decomposition was studied to probe the acid-base properties of the catalysts, Ti02 and Mo03 exhibi ted dehydration activity, whereas CoO showed dehydrogenation activity, All the supported catalysts gave activation energies for dehydration higher than dehydrogenation. In the sub-monolayer region, the catalytic activity for dehydration was in the order: MCT > CMTg > CMT > MT/C > CT/C, while the selectivity remained almost unchanged, In the monolayer region, the activity was: MT/C > CMT > CMTg > MCT > CT/C and the selectivity increased compared with the sub-monolayer region. In the four-monolayer reg ion, the activity decreased compared with the sub-monolayer and monolayer regions, but the selectivity increased relative to the previous two regimes. "Compensation effect 0, plots revealed different types of active centres responsible for dehydration and dehydrogenation processes in the MoOx /Ti02 and CoO-Mo03/Ti02 catalysts, while active centres were almost identical with the CoOx /Ti02 system.