Low-temperature selective transformation of diethylbenzene to isobutane and cyclohexanes via the interplay of Pt and acid centres in Pt/H-*BEA zeolites

Abstract

The hydrocracking of aromatic hydrocarbons on bifunctional catalysts comprises parallel reactions that provide a wide distribution of products and byproducts. This work demonstrates on diethylbenzene (DEB) hydrotreatment that Pt/H-Al-rich *BEA zeolite catalysts can significantly reduce the hydrocracking temperature so that only the selected reaction mechanisms prevail in the process, providing high selectivity. The interplay of high activity of Pt clusters in hydrogenation/dehydrogenation and Bronsted acid sites in acid-catalysed reactions allows selective hydrocracking of DEB to isobutane and methylcyclopentane by the paring reaction at 200 degrees C. Low-temperature hydrocracking consists of hydrogenation of DEB to diethylcyclohexane, its rapid skeletal hydroisomerization to C-10 branched alkylcycloalkanes followed by their A type beta scission providing isobutane and methylcyclopentane with 80% selectivity at 68% DEB conversion, practically without subsequent reactions of the formed products. The reactive C-C bond in tribranched alkylcycloalkanes selectively undergoes A type beta scission, while more stable C-C bonds in less or unbranched hydrocarbon chains or rings do not crack to a substantial extent at low temperatures. The study demonstrates that the low-temperature hydrotreatment of aromatics over highly active catalysts allows controlling the involvement of individual reaction mechanisms in the complex hydrocracking process and provides tailored selectivity. (C) 2022 Elsevier Inc. All rights reserved.