Improving the performance of ASA in the DAC of 2,5-DMF and ethylene

Abstract

A variety of methods are employed to synthesize amorphous silica–alumina (ASA) to resolve the role of Al speciation and surface area in the catalytic performance in the Diels–Alder cycloaddition reaction of 2,5-dimethylfuran and ethylene to p-xylene. ASA was prepared by homogeneous deposition–precipitation (HDP) of Al³⁺ on ordered mesoporous silica, i.e., SBA-15 and OMS prepared under hydrothermal synthesis conditions using an imidazole-based template, and one-step flame spray pyrolysis (FSP). IR spectroscopy and ²⁷Al MAS NMR showed that the resulting ASA represented a set of materials with distinct textural and acidic properties. ASA prepared by grafting Al to ordered mesoporous silica led to a much higher concentration of Brønsted acid sites (BAS). These samples performed much better in the DAC reaction, with p-xylene yields higher than those obtained with a HBeta zeolite benchmark. Materials with Al partially in the bulk of silica (OMS, FSP) and containing significant alumina domains are less acidic and exhibit much lower p-xylene yields. These findings point to the importance of Brønsted acidity for p-xylene formation. This study shows that careful design of the Al speciation can lead to amorphous silica–alumina with similar DAC performance to microporous zeolites.