Reaction pathways control of long-chain alkanes hydroisomerization and hydrocracking via tailoring the metal-acid sites intimacy

Abstract

Designing a bifunctional catalyst to achieve efficient hydroisomerization of long-chain alkanes is very essential for producing high-performance fuel and lubricant base oils. Herein, a bifunctional catalyst composed of an intimate mixture of ZSM-48 zeolite and alumina binder and with platinum (Pt) metal controllably deposited on zeolite or alumina was fabricated by a strong electrostatic adsorption method. The dependence of reaction pathways of hydroisomerization and hydrocracking of n-hexadecane on the metal-acid sites intimacy was investigated. High Brønsted acid density and suitable metal-acid sites intimacy favored to promote the catalytic activity. The selectivity, hydroisomerization mechanism and hydrocracking mechanism were significantly altered by tailoring the metal-acid sites intimacy. Too large or too small metal-acid sites intimacy was conducive to inhibit the occurrence of pore-mouth mode. A linear decease of the hydroisomerization selectivity with the increase of acid steps (nas) was observed. The catalyst with nanoscale intimacy of metal-acid sites (Pt/A-48) showed the highest catalytic activity and isomer selectivity (87%) and the least acid steps (nas = 1.4). This work provides a promising approach to fabricating highly efficient and shape-selective bifunctional catalysts for selective hydroisomerization of long-chain alkanes. A reaction network was proposed over the catalysts with different metal-acid intimacy.