Disclosed is making a particular inorganic crystalline vanadium III oxidic compound from a pentavalent vanadium compound and at least one other or more metal cations, which process comprises (1) reducing a pentavalent vanadium oxidic compound to the V.sup.III state by heating at 100.degree. C. or less an aqueous medium slurry or solution of said pentavalent compound containing a reducing agent selected from hydrazine and hydrocarbylhydrazine, (2) providing in said aqueous medium, either before, during or after said reducing step, said other metal cation(s) in solution in the ratio called for by said particular crystalline compound, (3) removing the liquid aqueous medium, and (4) calcining the resulting dry solid at a temperature in the range from 400.degree. to 800.degree. C. in an inert atmosphere.Also disclosed is the vapor phase catalytic dehydrogenation of paraffins using certain spinels and perovskites as catalysts.