Characterization and reactivity of molybdenum oxide catalysts supported on anatase and rutile polymorphs of titania Original Research Article

A series of MoO3 catalysts with Mo loadings, ranging from 2–12% w/w, supported on TiO2 (anatase) and TiO2 (rutile) were investigated by X-ray diffraction, temperature programmed reduction (TPR), 1H magic angle spinning (MAS) NMR and oxygen chemisorption measurements. Dispersion of molybdena was determined by the oxygen chemisorption at 623 K and by a static method on the samples prereduced at the same temperature. At low Mo loadings, i.e. below 6% Mo, molybdenum oxide was found to be present in a highly dispersed state. Oxygen chemisorption results suggest that MoO3 particles disperse better on TiO2 (anatase) than when they are supported on TiO2 (rutile). 1H magic-angle-spinning NMR spectra of MoO3 catalysts supported on anatase and rutile polymorphs reveal the presence of two types of OH groups on the surface: OH groups of acidic nature and the basic OH groups. Temperature programmed reduction profiles of MoO3/TiO2 samples suggest that the reduction of MoO3 to Mo proceeds in two stages and the reducibility of MoO3 increases with Mo loading in the catalysts. The catalytic properties were evaluated for the vapor-phase ammoxidation of 3-picoline to nicontinonitrile and are related to oxygen chemisorption sites on the surface.