There are a number of differences between thermal and catalytic cracking, but the main ones are the variation in temperature and pressure used in the processes. Both processes are used in the refining of petroleum to break down hydrocarbon molecules. This is one of the principle ways crude oil is turned into gasoline.
With catalytic cracking, a catalyst is used to yield results with much less severe operating conditions. This process breaks the molecules down into lighter products during the cracking operation. Thermal cracking uses high heat, usually around 800 degrees Celsius, along with high pressure of around 70 atmospheres to break down the molecules. This process produces a lot of solid waste, which lead to the development of other processes such as catalytic cracking.