Certain crystalline aluminum borate catalyst supports containing about 8-25 weight-percent of B2O3 are found to provide unusually stable and active catalysts for high-temperature chemical conversions, particularly exhaust gas conversion, when prepared by precalcining shaped composites of alumina and boria at temperatures between about 1,250* and 2,600*F., prior to the addition thereto of active metal or metals. Calcination at below 1,250*F. is found to yield amorphous catalysts of inferior activity, while at temperatures above 2,600*F. drastic reductions in surface area may occur.