Fabrication of sea urchin-like hierarchical porous SAPO-11 molecular sieves toward hydrogenation of lipid to jet fuel

Abstract

Hydrogention of lipid to jet fuel especially iso-alkanes is considered as a promising technology to improve the cold-flow properties of bio-jet fuel. In this study, we successfully synthesized a hydroisomerization catalyst that is based on a SAPO-11 molecular sieve (SAPO-11-A-6) with a sea urchin-like and hierarchical porous structure. SAPO-11-A-6 was fabricated with an Al : cetyltrimethylammonium bromide (CTAB) ratio of 0.006 after pre-crystallization using an in situ seed-induced steam-assisted method (SISAC). The SAPO-11-A-6 molecular sieves exhibited abundant mesopores, a larger external surface area, and more acidic sites than SAPO-11-S molecular sieves without CTAB. After loading nickel nanoparticles by using a citric-acid-assisted impregnation method, the hydrogenation of oleic acid results indicated that among the series of Ni/SAPO-11 catalysts, a maximum of 78.2% isomer selectivity was achieved by the Ni/SAPO-11-A-6 catalyst under reaction conditions of 360 °C, 4 h, and 4.0 MPa H₂. The crystal formation route of the sea urchin-like hierarchical porous SAPO-11 was proposed: after pre-crystallization, the cationic surfactant CTAB entered the layered semi-crystalline phase, contributing to the formation of the novel sea urchin-like mesoporous SAPO-11 structure.