Process for producing fluid catalyst having good activity from coarse catalyst

A process for producing a fluid catalyst having good activity from a coarse catalyst wherein said fluid catalyst is suitable for oxidation, ammoxidation or oxidative dehydrogenation reaction of hydrocarbons which comprises

• crushing a fluid catalyst, a greater part of which is composed of particles having a large particle size, to produce finely-divided particles,
• adjusting the distribution of particle size of said catalyst so that the amount of particles of a size of about 20.mu. or less is about 30% by weight or less of the total weight of catalyst particles and the amount of particles having a weight average particle size (particle size at median (50%) by weight of the total weight of catalyst particles in the particle size distribution) is 90% by weight or less of the total weight of the catalyst particles, and
• thereafter calcining said catalyst at a temperature of about 500.degree. C.-about 1000.degree. C. under a non-reducing atmosphere.