The demand for high performance gasoline and other petroleum fuels for use in the second world war brought about the catalytic refinery. The catalytic refinery moved petroleum refining from free radical reactions to ionic reactions. This marked the age of the catalytic refinery which was the focus of many refineries up until the 1970’s. This also brought into existence the petrochemical industry. The advent of catalytic refineries introduced catalytic cracking, reforming, alkylation, and polymerization which increased the production of the highly desired high octane number gasoline. During this time the use of hydrotreatment was essential to keep the platinum catalysts from being contaminated from sulfur which was found in the crude. What made the catalytic process so great for its time was the ability to increase product yield and selectivity. This produced large quantities of LPG and took advantage of alkylation which increased gasoline octane and yield which was highly desired as aviation gasoline. Fluid catalytic cracking, which begin in 1942, also increased gasoline yield and octane number while delivering petrochemical feedstocks as a byproduct which allowed the production of many products using petrochemicals.