Carbon Deposit Analysis in Catalyst Deactivation, Regeneration, and Rejuvenation

• Published in: Angewandte Chemie International Edition Vol. 62; no. 29; pp. e202300319 - n/a
• Main Authors: Vogt, Eelco T. C., Fu, Donglong, Weckhuysen, Bert M.
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 17.07.2023
• Edition: International ed. in English
• Subjects: Alkenes; Carbon; Carbon Deposition; Catalyst Deactivation; Catalyst Design; Catalysts; Coke; Coke Analysis; Deactivation; Geographical distribution; Structure-function relationships; Zeolites; Catalyst Deactivation; Carbon Deposition; Coke Analysis; Coke; Catalyst Design
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.202300319

Hydrocarbon conversion catalysts suffer from deactivation by deposition or formation of carbon deposits. Carbon deposit formation is thermodynamically favored above 350 °C, even in some hydrogen‐rich environments. We discuss four basic mechanisms: a carbenium‐ion based mechanism taking place on acid sites of zeolites or bifunctional catalysts, a metal‐induced formation of soft coke (i.e., oligomers of small olefins) on bifunctional catalysts, a radical‐mediated mechanism in higher‐temperature processes, and fast‐growing carbon filament formation. Catalysts deactivate because carbon deposits block pores at different length scales, or directly block active sites. Some deactivated catalysts can be re‐used, others can be regenerated or have to be discarded. Catalyst and process design can mitigate the effects of deactivation. New analytical tools allow for the direct observation (in some cases even under in situ or operando conditions) of the 3D‐distribution of coke‐type species as a function of catalyst structure and lifetime. This review article discusses the role of carbon species deposited from various feedstock molecules or formed over time during a catalytic process, including ways to mitigate the effects of these carbon species by catalyst design, regeneration or rejuvenation. This is done for various industrially relevant systems, including the methanol‐to‐hydrocarbons process. New tools for the direct observation of the 3D‐distribution of carbon species within the catalyst pore network are also described.