HYDROCARBON CONVERSION CATALYSTS OF IMPROVED ACTIVITY ARE OBTAINED BY ACTIVATING FORMAMINOUS REFRACTORY OXIDES COMBINED WITH AT LEAST ONE THERMALLY DECOMPOSABLE AND/ OR OXIDIZABLE COMPOUND OF A CATALYTICALLY ACTIVE METAL UPON CALCINATION WHILE CONTACTING THE COMPOSITE WITH AN ACCELERATED FLOW OF AN OXIDIZING GAS AT A RATE OF AT LEAST ABOUT 2 S.C.F.M. PER POUND OF SAID COMPOSITE. FURTHER ADVANTAGE IS REALIZED BY HEATING THE COMPOSITE TO THE PRESCRIBED CALCINATION TEMPERATURE AT A CONTROLLED GRADUAL RATE. IT IS ALSO GENERALLY DESIRABLE TO ASSURE THAT THE INLET TEMPERATURE OF THE OXIDIZING GAS PRIOR TO CONTACT WITH THE COMPOSITE IS LESS THAN ABOUT 500*F.