Characterization and reactivity of molybdenum oxide catalysts supported on zirconia Original Research Article

A series of MoO3/ZrO2 catalysts with Mo loading varying from 1 to 12 wt.% was prepared. Each catalyst was characterized by oxygen chemisorption, X-ray diffraction (XRD), electron spin resonance (ESR), temperature programmed reduction (TPR), and temperature programmed desorption (TPD) of ammonia. X-ray diffraction patterns indicate the presence of a microcrystalline molybdena phase at higher loadings. Dispersion of molybdena was determined by the oxygen chemisorption at 623 K, using a static method on the samples prereduced at the same temperature. At low Mo loadings, i.e. <7.5%, molybdenum oxide is found to be present in a highly dispersed state. ESR results suggest the presence of Mo5+ in the reduced catalysts. TPR results suggest that the reducibility of MoO3 increases with the increase of Mo loading in Mo/ZrO2 catalysts. TPD of ammonia results suggest that the acidity of the catalysts is increasing with the increase of molybdena loading. The catalytic properties were evaluated for the vapor-phase ammoxidation of 3-picoline to nicotinonitrile and were found to be related to oxygen chemisorption sites.