Bifunctional catalysts exhibiting significantly enhanced isomerization yields were synthesized by combining Pt-impregnated γ-Al₂O₃ with ZSM-23 zeolite. The structures of the di-branched products were meticulously characterized. Furthermore, the influences of thermodynamic stability, zeolite pore structure, and substrate carbon number on product distribution were analyzed concerning the spacing of branched chains.

Abstract

Hydroisomerization of long-chain alkanes is a crucial process in producing high-performance fuel and lubricant base oils. The challenge in this process is enhancing catalytic performance by optimizing the intimacy between metal and Brønsted acid sites in bifunctional catalysts. In this study, a series of bifunctional catalysts with varying metal–acid site intimacy was prepared by depositing platinum (Pt) on the ZSM-23 zeolite or γ-Al₂O₃ surface. The Pt/A + Z catalyst, exhibiting moderate intimacy, demonstrated superior catalytic performance in the hydroisomerization of n-hexadecane, achieving up to 64 ± 0.8% i-C₁₆ yield at 89 ± 0.5% conversion. The optimized metal–acid site intimacy facilitated the desorption of reaction intermediates, minimizing cracking at the acid sites and thus improving selectivity. Further analysis revealed that product distributions were closely related to the pore structure of zeolites. Specifically, the formation of di-branched isomers during the isomerization of n-hexadecane, n-dodecane, and n-octane was influenced by the type of zeolite support (ZSM-23, ZSM-48). The present study proposes a direct method to enhance the hydroisomerization performance while reducing the cost of the catalyst. By determining di-branched products more precisely, it introduces a novel approach for evaluating products based on branch chain spacing. Additionally, the combined effects of catalyst structure and thermodynamic stability on product distribution were investigated, along with the influence of reactant stay time.