A high-surface-area silicoaluminophosphate material rich in Brönsted acid sites as a matrix in catalytic cracking

Abstract

A transparent gel-like mesoporous silicoaluminophosphate material (SAP) with a Si/Al molar ratio of 20 was synthesized by hydrothermal method. The physicochemical features of SAP were characterized by XRD, XRF, BET, SEM and FT-IR spectroscopy of pyridine adsorption techniques. The results indicated that incorporation of phosphorus (P) into aluminasilica system altered the basic textural characteristics of aluminasilica. Especially after hydrothermal treatment, the material with large special surface area (up to 492 m2/g) exhibited a good performance on hydrothermal stability. Moreover, the phosphorus modifier can not only increase the amount of Brönsted acidic sites (up to 48.44 μmol/g) and the percentage of weak acidic sites in total acidic sites, but also regulate the acid type, such as the ratio of B/L (Brönsted acid/Lewis acid) increases to 1.15. The performances of samples as matrices for the catalytic cracking of heavy vacuum gas oil (VGO) were investigated. At 520 °C, the catalysts showed much higher gasoline and diesel oil yields achieving to 45.59 wt% and 19.20 wt%, respectively, and lower coke selectivity (2.86%) than conventional FCC matrices, such as kaolin and amorphous silica-alumina.