Olefins selected from the group consisting of propylene, isobutylene or mixtures thereof, are converted to acrylonitrile, methacrylonitrile, and mixtures thereof in a process comprising reacting in the vapor phase at an elevated temperature and pressure said olefin with a molecular oxygen containing gas and ammonia in the presence of a catalytic composition comprising a complex of metal oxides comprising bismuth, molybdenum, iron, cerium and other promoter elements, wherein the X-ray diffraction pattern of the catalytic composition has X-ray diffraction peaks at 2θ angle 28±0.3 degrees and 2θ angle 26.5±0.3 degrees, and wherein the ratio of the intensity of the most intense x-ray diffraction peak within 2θ angle 28±0.3 degrees to the intensity of most intense x-ray diffraction peak within 2θ angle 26.5±0.3 degrees is defined as X/Y, and wherein X/Y is greater than or equal to 0.7.