Characterization of MoO3/TiO2 (Anatase) catalysts by ESR, 1H MAS NMR, and oxygen chemisorption

A series of molybdena catalysts supported on anatase titania with Mo loadings ranging from 2 to 12 wt % were investigated by H-1 MAS NMR, XRD, ESR, and oxygen chemisorption. H-1 MAS NMR spectra reveals the presence of two types of OH groups (acidic and basic) on TiO2. Dispersion of molybdena was determined by the oxygen chemisorption at 623 K through a static method on the samples prereduced at the same temperature. At low Mo loadings, i.e., below 6% Mo, molybdenum oxide is found to be present in a highly dispersed state. A comparison of the dispersion of molybdena determined by low-temperature oxygen chemisorption (samples reduced at 773 K for 6 h and subsequent oxygen chemisorption at 195 K) with that determined at 623 K shows that the latter method provides a better measure of the dispersion of molybdena. ESR results suggest the presence of Mo5+ in the reduced catalysts.