Comulled silica-alumina base denitrification catalyst

An extruded silica-alumina catalyst prepared by the method which consists essentially of the following steps:

• mixing a sodium silicate solution with an aqueous aluminum sulfate solution and sulfuric acid to form an acidified silica sol in an alumina salt solution having a pH in the range of about 1 to 3;
• adding sufficient ammonium hydroxide to said acidified silica sol in the aluminum salt solution to form a cogelled mass of silica and alumina under substantially constant pH conditions and at a pH of at least 4;
• adding additional ammonium hydroxide to the cogelled mass to obtain a pH in the range of 7.5 to 8.5;
• washing the cogelled mass;
• mulling the cogelled mass with a peptizing agent, a Group VI-B metal compound and a Group VIII metal compound to form an extrudable dough;
• extruding said dough;
• and drying and calcining the extruded dough.