Structural and catalytic characteristics of MoO3/CeO2 catalysts: CO oxidation activity

The 8 wt.% MoO3-modified CeO2 materials were prepared by three different methods namely, impregnation, wet mechanical mixing and co-precipitation and characterized by thermal analyses (TG and DTA), X-ray diffractometry, infrared spectroscopy, UV-vis diffuse reflectance spectroscopy as well as nitrogen sorptometry. Their catalytic activities in the oxidation of CO to CO2 were also examined. The results showed that the material prepared by co-precipitation provided the highest activity, comparatively. This was due to the concomitant strong metal oxide-support interaction revealed for this material that validated by XRD and FTIR results those showed diminishing in particles size of the two ions and formation of MoOCe linkages (760 cm−1), respectively. The UV-vis spectrum of this material showed the predominant presence of tetrahedral Mo6+ reflecting the highest dispersion among all samples. This material exhibited as well the highest specific surface area (96 m2/g) and rather presented mesopores of regular distribution. Important correlations between the latter material and those prepared by impregnation and wet mechanical mixing in view of proposed interaction between ions, morphology, surface texturing and their effects on the activity of CO oxidation were evaluated and discussed. It is inferred that surface molybdate that permit the formation of Mo6+ in highly dispersed state beside the Ce3+/Ce4+ redox couples were responsible for the revealed catalytic activity.