Intermolecular hydrogen transfer reactions as key stages in the catalytic cracking: achievements and outlook

The review summarizes and critically analyzes the results of exploratory and basic studies carried out mainly in the last 10 years concerning the mechanism and role of hydrogen transfer reactions in hydrocarbon conversion processes. A discussion addresses the established views on the regularities of these reactions (mainly involving hydrogen–hydrogen, carbon–carbon and carbon–hydrogen bonds) in various systems containing cations of d-, p - and s-elements. The features of intermolecular hydrogen transfer reactions involved in the zeolite-catalyzed cracking of hydrocarbons are considered. Data on the development of compositions and investigation of properties of modern zeolite-based catalysts for hydrocarbon cracking are discussed. The attention is focused on the role of intermolecular hydrogen transfer in this process, especially in the transformations of heteroatomic compounds. Regarding zeolite compositions, the main attention is paid to the influence of the acid site distribution on the zeolite surface on the hydrogen transfer reactions and the role of extra-framework aluminium species and added modifier cations in these processes. The results of studies of hydrogen transfer by model calculations and by drawing analogies are presented. It is demonstrated that intermolecular hydrogen transfer reactions must be taken into account while addressing problems of improving the cracking catalysts and creating catalytic compositions for joint processing of sulfur, nitrogen and oxygen compounds together with hydrocarbons in the catalytic cracking.
The bibliography includes 249 references.