One-step desilication-recrystallization towards enhanced diffusion for Ni/ZSM-5-catalyzed n-hexane hydrogenative isomerization

Abstract

The hydrogenative isomerization of n-alkanes to their branched isomers over bifunctional catalysts, an effective approach for green gasoline and diesel production, has gained increasing interests in the petrochemical industry. A rational strategy for catalyst development has been proposed and demonstrated with a more favorable mass transfer of isomerization products. Such strategy comprises consecutive desilication/recrystallization upon the parent ZSM-5 zeolite, which generates a hierarchical porous structure. The following incorporation of Ni species ensures the proximity of the metallic and protic active sites, which catalyze the dehydrogenation/hydrogenation and skeletal isomerization steps, respectively. The above structural features of the new Ni/ZSM-5-DR catalyst have been evidenced by various characterization methods. Regarding the changes in the reaction network, the intrinsic rate constant and activation energy are not influenced by the new porous structure, but the mass transfer property of different reagents shows significant distinction. It is further supported by the overall apparent kinetic behavior that diffusion-limited region has been shifted towards higher temperatures after the introduction of the new porous structure. The results of individual diffusion coefficients and overall product distribution provide final evidence of the proposed scenario. As a result, the catalyst development leads to the preferred isomerization product distribution with high selectivity.