Flexible Regulation of Product Distribution in Cyclohexane Cracking Catalyzed by Acid–Base Bifunctional Catalyst

Conversion of crude oil to chemicals is a developing trend in the petroleum industry. Cycloalkanes are main components of crude oil, especially in intermediate- or naphthene-based oil; however, converting cycloalkanes into high-value chemicals, especially light olefins, remains a challenge. In this study, HIM-5 zeolite, with strong Brønsted acidity, small pores, and a large-cavity structure, was proposed as the active material for cyclohexane (a model compound for cycloalkanes) cracking. The external surface of HIM-5 was modified with phosphorus (P) to reduce the acid strength, efficiently improving the catalytic lifetime. To regulate product distribution, an acid–base bifunctional catalyst composed of calcium aluminate (CA) and the most stable zeolite, 1.0P-CIM, was prepared. As the 1.0P-CIM content decreased, the acid amount exhibited an obvious decreasing tendency, while the base amount exhibited the opposite trend. The average light olefins yield over the bifunctional catalysts varied from 11.9–27.8%, while the average BTX (benzene, toluene, xylene) yield was from 31.4–41.6%. Specifically, the light olefins yield in the catalytic system containing 30 wt % zeolite was the highest (27.8%), with an increase of 15.9% compared with that in the 1.0P-CIM system, and the total yield of light olefins and BTX reached the maximum (59.2%). In situ spectroscopic analysis illustrated that CA could activate the reactant, promote ring-opening, and inhibit side reactions such as hydrogen transfer, leading to increased light olefins yield, while the strong acidity of the bifunctional catalyst, when CA content was low, would facilitate BTX formation. Therefore, product distribution could be flexibly adjusted in cyclohexane cracking by changing the acid or base amount in the bifunctional catalyst.