Citric-acid-induced mesoporous SAPO-11 loaded with highly dispersed nickel for enhanced hydroisomerization of oleic acid to iso-alkanes

Abstract

In this study, a series of Ni/SAPO-11 catalysts with different Ni loadings were prepared by citric acid-assisted impregnation for the hydroisomerization of oleic acid to iso-alkanes. Serving as a chelating ligand, citric acid first promoted the dispersion of Ni nanoparticles loaded on SAPO-11. Because of its acid properties, citric acid facilitated the removal of aluminium oxide species, contributing to the formation of a mesoporous SAPO-11 structure. A maximum of 67.3 mol% of iso-alkanes was formed using 7Ni/SAPO-11 as a catalyst under optimal conditions of 360 °C, 4 h, and 4.0 MPa H2. After reusing for five cycles, the catalyst still exhibited 21.5 mol% isomer selectivity. The reaction pathways and catalytic mechanisms concerning the oleic acid hydroisomerization process were proposed and discussed. The hydroisomerization of oleic acid mainly depended on the catalyst's Lewis acid sites, with the assistance of the metal centre and Brönsted acid sites. The mesoporous structure of SAPO-11 facilitated the availability of a significant number of catalytic Lewis acid sites, which, together with the highly dispersed Ni centres, contributed to the enhanced product isomerization.