Effect of the nature of the support on molybdenum catalytic behavior in diesel particulate combustion (original) (raw)

Mo/Si02 and Mo/Ti02 catalysts with three different molybdenum contents were prepared using non-porous supports and the thermal spreading method for the combustion of a particulate material (PM). The results of scanning electron microscopy (SEM) and N2 adsorption/desorption techniques showed that the thermal spreading preparation method does not induce relevant textural changes on the supports. X-ray diffraction (XRD) results showed the occurrence of thermal spreading of Mo03 onto silica and titania supports. Diffuse reflection spectroscopy (DRS) results provided clear evidence of different Mo species on these systems: highly dispersed species on the silica catalysts and polymolybdates on the titania catalysts. It may be inferred that when prepared by the thermal spreading method the nature of the support determincs the kind of molybdenum species formed in these catalysts, irrespective of the Mo content. The reactive data were evaluated by differential scanning calorimetry (DSe), using a physical mixture of PM and the catalysts. The silica-supported catalysts showed higher reactivity for PM combustion than the titania-supported ones, being the most active the systems with the Mo monolayer. The results suggested that the dispersed species are far more active than the polvmolybdates or Mo03 itself.