Abstract
Isomorphic substitution or post-synthesis incorporation of hafnium into KIT-6 mesoporous material has been fabricated for the first time in highly acidic media using triethylamine hafnium pentachloride ionic liquid (TEA-HfCl5) as a novel hafnium precursor ionic liquid (Si/Hf molar ratio of 90). The prepared catalysts were characterized by X-ray diffraction, Fourier transfer infrared (FT-IR), pyridine-FT-IR, N-2-adsorption, transmission electron microscopy and the surface acidity was tested by temperature programmed desorption (NH3-TPD) of ammonia. The effect of the nature of hafnium source in the KIT-6 synthesis has been investigated using different hafnium source, viz., triethylamine hafnium pentachloride ionic and hafnium chloride. Triethylamine hafnium pentachloride ionic was found to be the better hafnium source for HfKIT-6 material synthesis and enhanced the amount of hafnium incorporation in the KIT-6 silica walls. ICP-AES studies evidenced that the proportion of Hf4+ increases using triethylamine hafnium pentachloride ionic. The catalytic performance of SO4 (2-)/HfKIT-6 was investigated by cracking of 1,3,5-triisopropylbenzene, esterification of acetic acid with n-butanol, while Pd/SO4 (2-)/HfKIT-6 was examined by n-C-7 isomerization reaction. Our findings indicated that HfKIT-6 prepared by ionic liquid approach offered distinct structural and surface features, particularly in terms of Bronsted and Lewis acid site contents. As compared with SO4 (2-)/HfKIT-6 (direct ionic liquid) and SO4 (2-)/HfKIT-6 (direct), SO4 (2-)/HfKIT-6 prepared by post ionic liquid exhibited higher yield percentage of 1,3,5-triisopropylbenzene cracking and n-butyl acetate yield. Furthermore, Pd/SO4 (2-)/HfKIT-6 catalyst prepared by post ionic liquid shows high isomerization activities compared with Pd/SO4 (2-)/HfKIT-6 prepared by direct method using TEA-HfCl5 ionic liquid or HfCl4 materials.