Cracking catalysts containing silica-alumina gels

A method of producing silica-alumina catalyst which comprises mixing in a reaction mixture sodium silicate with a combination of anionic and cationic aluminum salts in such amounts as to provide an SiO.sub.2 /Al.sub.2 O.sub.3 mole ratio in the mixture in the range of about 1 to 3 moles of SiO.sub.2 per mole of Al.sub.2 O.sub.3 based on the total Al.sub.2 O.sub.3 content of the combination of anionic and cationic aluminum salts;

• of the total quantity of Al.sub.2 O.sub.3 provided by the combination of aluminum salts, less than 95% by weight and more than 50% by weight is selected from anionic aluminum salts, the balance from cationic aluminum salts;
• adding ammonium hydroxide to the said mixture and adjusting the pH in the mixture to a range of about 9 to about 10, thereby forming an ammoniated silica-alumina gel, separating said gel and mixing said gel with a water solution of a polyvalent or a monovalent cation other than alkali metal cation, subjecting said solution to hydrothermal treatment at superatmospheric pressure and reducing the NH.sub.4 content associated with said ammoniated gel to substantially less than 0.3 equivalents of NH.sub.4 per mole of Al.sub.2 O.sub.3, separating and drying said gel.