Synthesis of amorphous silica-alumina with enhanced specific surface area and acidity by pH-swing method and its catalytic activity in cumene cracking

Abstract

High-performance amorphous silica-alumina (ASA) is an important acid material in the chemical industry. In this work, we successfully synthesized mesoporous ASA with enhanced specific surface area, Lewis acidity and total acidity by pH-swing method. The morphology and structure of ASA were systematically investigated. With the increase of SiO2 content from 20.1% to 67.0%, the morphology of ASA varied considerably from fibrous to granular, and the specific surface area decreased from 436 to 306 m2 g−1. Meanwhile, the gradual increase of surface silanol groups facilitated the formation of pseudo-bridged silanol groups and promoted the formation of Brønsted acid sites (BAS). Furthermore, the concentration of BAS was found to increase with increasing tetra- and penta-coordinated aluminum and decrease with increasing octa-coordinated aluminum. In addition, the acidity-activity relationship was also explored by applying the as-synthesized ASA samples directly to the cracking reaction of cumene. The results showed that the activity of ASA was proportional to the concentration of BAS. The pH-swing method can controllably synthesize ASA materials with different structures and acidity for petrochemical industry.