Characterization of MoO₃/TiO₂(Anatase) Catalysts by ESR,¹H MAS NMR, and Oxygen Chemisorption

Abstract

A series of molybdena catalysts supported on anatase titania with Mo loadings ranging from 2 to 12 wt % were investigated by 1H MAS NMR, XRD, ESR, and oxygen chemisorption. 1H 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.