The Reaction Mechanism of Catalytic Cracking: Quantifying Activity, Selectivity, and Catalyst Decay

Abstract

Catalytic cracking has reached technological maturity without the benefit of a fundamental understanding and quantification of its elementary processes. Without this understanding, advances in this field have become increasingly rare and will be even more difficult to achieve in the future. This article offers a basis for the development of a fundamental understanding of catalytic cracking. It ties together all of the principal phenomena in catalytic cracking and lays a foundation for their quantification on the basis of the following postulates. 1. All important processes involved in the suite of reactions which fall under the generic name of “catalytic cracking” proceed via the mediation of surface-resident ions. 2. These ions undergo only two types of reactions and produce all the major gas-phase products: (a) Bimolecular disproportionations with neutral gas-phase molecules, or with neutral portions of neighboring carbenium ions, via the formation of pentacoordinated carbonium ion intermediates (b) monomolecular decompositions of carbenium ions 3. All the reactions involved in the major processes of catalytic cracking proceed on locations corresponding to the Brgnsted acid sites originally present on the catalyst.