Role of fluoride ions in synthesis and isomerization performance of superfine SAPO-11 zeolite

Abstract

In presence of fluoride ions, superfine silico-alumino-phosphate-11 zeolite was synthesized via steam-assisted conversion method. The samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, nitrogen sorption, pyridine adsorption Fourier transform infrared spectroscopy, magic angle spinning nuclear magnetic resonance spectroscopy and dynamic light scattering techniques. The results show that the fluoride ions decrease particle size and induce inorganic species to achieve oriented growth. The resulting rod-like SAPO-11 crystalline particles are 500nm in length and acid sites are controlled by mass ratio of fluoride ions in the initial gel. The catalytic isomerization of superfine SAPO-11 was evaluated using n-dodecane and vacuum gas oil as feed streams. The catalysts with SAPO-11 promoter exhibit more iso-hydrocarbon in the gasoline compared to catalysts without promoter. Of note is the higher coke resistant ability of catalyst with SAPO-11 due to high electronegativity of fluoride ions. Desorption of coke precursor is easier from catalyst with promoter than that without promoter. The role of fluoride ions is to inhibit coke deposition by suppressing condensation reactions.