A series of molybdenum oxide catalysts with Mo loadings in the range 2.5-12.5 wt % Mo supported on La2O3-stabilized ZrO2 was prepared by impregnation. X-ray diffraction results of the catalysts showed the diffraction patterns of crystalline MoO3 from 10 wt % Mo. Dispersion of molybdena was determined by the oxygen chemisorption method, and it was found to decrease with an increase in Mo loading due to formation of MoO3w crystallites at higher Mo loadings. Temperature-programmed reduction results suggest that the reducibility is found to decrease with Mo loading as a result of the decrease in dispersion. The acidity of the catalysts was found to increase with Mo loading, and the activity of the catalysts also found to increase with the increase in Mo loading up to 7.5 wt % Mo loading. Laser Raman spectra of the catalysts show the Raman bands due to MoO3 from 7.5 wt % Mo at 819 and 997 cm(-1). At lower Mo loadings, highly dispersed species were observed. The catalytic properties were evaluated during the ammoxidation of toluene to benzonitrile and were related to the oxygen chemisorption sites on the support surface.