Synthesis and characterization of amorphous silica-alumina with enhanced acidity and its application in hydro-isomerization/cracking

Abstract

Amorphous silica-aluminas with enhanced Brønsted acidity have been successfully synthesized via a novel acetic acid based sol-gel process. The resulting amorphous silica-aluminas possess an irregular spherical morphology, homogeneously element dispersion, and a high external surface area in the range of 374–594 m2/g with little contribution from micropores. By simply adjusting the molar Si/Al ratio in the synthesis precursor solution from 0.5 to 2.0, the total Brønsted acid site density firstly increases and then slightly decreases, consistent with the trend of summarized molar content of four and five-coordinated aluminum species. Among them, the amorphous silica-alumina with initial Si/Al ratio of 1.5 exhibits the highest Brønsted acid site density, and its supported Pt catalyst performs the highest activity resembling that of HBeta-based catalyst in the hydroisomerization of n-hexadecane. Meanwhile, a superior catalytic selectivity to multibranched isomers was received over the amorphous silica-alumina without strong Brønsted acid sites. Moreover, a remarkable stability (>2000 h) was also achieved in the hydrocracking of Fischer-Tropsch wax under industrially relevant reaction conditions. This sol-gel synthesis process provides a facile method to prepare amorphous silica-aluminas with outstanding texture and acid properties for catalytic refining in petrochemical fields.