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Why is coke burned off the catalyst in a catalytic cracking regenerator?

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Aerial view of an oil refinery complex near New Orleans, Louisiana, with storage tanks, industrial structures, and smoke rising from the facility, surrounded by open land. — petroleum refining Aerial view of an oil refinery near New Orleans.

In the process of catalytic cracking, carbon—often referred to as coke—is deposited on the surface of the catalyst particles as cracking reactions occur. This deposition is problematic because it blocks the active sites of the catalyst, which impairs the efficiency of the chemical reaction.1

To maintain the catalyst's activity and the overall efficiency of the unit, the spent catalyst is continuously withdrawn and transferred to a regenerator vessel. In this vessel, the coke is burned off using a current of air. This regeneration process serves two critical purposes:1

Restoration of Activity: By removing the carbon deposits, the active sites on the catalyst are cleared, allowing it to function effectively once reintroduced to the reactor.1
Heat Supply: The high-temperature combustion of the coke (typically 675–785 °C) heats the catalyst to the necessary temperature required for the cracking of fresh feedstock when it is returned to the reactor.1