Influences of the metal-acid proximity of Pd-SAPO-31 bifunctional catalysts for n-hexadecane hydroisomerization

Abstract

Hydroisomerization of n-alkanes over bifunctional catalysts is an effective approach for clean fuel production. However, it is still challenging to achieve metal-acid synergy and enhance the catalytic performance by preparation of bifunctional catalysts with suitable proximity between the metal sites and Brønsted acid sites. In this work, three series of bifunctional catalysts with different metal-acid proximities are prepared simply by mixing of SAPO-31 supported Pd (xPd/S) and γ-Al2O3 powders (xPd/S-A(C)), γ-Al2O3 supported Pd samples (xPd/A) and SAPO-31 powders (xPd/A-S(M)), and the mechanical mixing of shaped xPd/A and SAPO-31 granules (xPd/A-S(F)), respectively. The physico-chemical properties and the catalytic performance for the hydroisomerization of n-hexadecane have been investigated. Compared with the xPd/S-A(C) catalysts with the closest proximity between two active sites, the xPd/A-S(M) catalysts with moderate proximity at the micrometer scale demonstrate enhanced catalytic performance in the n-hexadecane hydroisomerization at temperatures above 340 °C. Inparticular, for the 0.15Pd/A-S(M) catalyst with a loading of 0.15 wt% Pd, the highest iso‐hexadecane yield of 80.4% was obtained at the n-hexadecane conversion of 90.4%. Therefore, this work provides an effective route for the simple preparation of bifunctional catalysts with lower Pd loading and favorable metal-acid balance for highly selective hydroisomerization of long-chain n-alkanes.