Characterization and reactivity of molybdenum oxide catalysts supported onanatase and rutile polymorphs of titania

A series of MoO3 catalysts with Mo loadings, ranging from 2-12% w/w, suppor ted on TiO2 (anatase) and TiO2 (rutile) were investigated by X-ray diffract ion, temperature programmed reduction (TPR). H-1 magic angle spinning (MAS) NMR aisi oxygen chemisorption measurements. Dispersion of molybdena was de termined 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 stat e. Oxygen chemisorption results suggest that MoO3 particles disperse better on TiO2 (anatase) than when they are supported on TiO2 (rutile). H-1 magic -angle-spinning NMR spectra of MoO3 catalysts supported on anatase and ruti le 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 MoO2/TiO3 samples suggest that the reductability of MoO3 increases with Mo loading in the catalysts. the reduction of MoO3 to M o proceeds in two stages and the hi 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. (C) 2001 Elsevier Sc ience B.V. All rights reserved.