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Why does carbon buildup reduce the effectiveness of reforming catalysts?

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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 catalytic reforming, carbon buildup—often referred to as coke—reduces the effectiveness of the catalyst by causing a gradual deterioration of the product yield pattern.1

As the reforming process proceeds, minute amounts of carbon are deposited on the surface of the catalyst pellets. This accumulation interferes with the catalyst's ability to promote the necessary chemical reactions, such as the breaking down of long-chain hydrocarbons and the conversion of naphthenes into high-octane aromatic compounds.1

To maintain efficiency, refineries must periodically remove these deposits. This is achieved either through semiregenerative processes, which require periodic shutdowns to burn off the carbon, or through continuous regeneration systems that circulate the catalyst through a separate vessel to remove the carbon and rejuvenate the material for continued use.1