ABSTRACT The molecular diffusion behaviors in catalytic systems can influence product selectivity. Such a phenomenon, analogous to shape selectivity in zeolite catalysis, can be referred to as diffusion‐selectivity. However, diffusion‐selectivity is often neglected, and its connotation has scarcely been revealed. Herein, a tandem diffusion system of n‐alkene and i‐alkene intermediates in catalytic hydroisomerization was precisely modulated for the demonstration of intermediate diffusion‐selective effects. In a series of Pt/zeolite composites, the diffusion distance of n‐alkene intermediates from Pt sites towards zeolitic acid sites was prolonged by depositing Pt nanoparticles at the external surface of zeolite, leading to a reduced surface permeability by 20%, which facilitated the dispersion of n‐alkene intermediates and mitigated side‐reactions. On the contrary, the diffusion length of i‐alkene intermediates inside zeolites decreased with reduced channel length, resulting in an enhanced intracrystal diffusion by two orders of magnitude, which avoided the long‐time residence in zeolite and thus the secondary cracking of i‐alkene intermediates. In this case, a high isomer yield of 62% can be obtained, outperforming the counterparts and those reported in the literature. The proposed diffusion‐selective catalysis can be generalized to reactant and product diffusion‐selectivity.
Yi et al. (Mon,) studied this question.