Amorphous Silica-Alumina as Suitable Catalyst for the Diels-Alder Cycloaddition of 2,5-Dimethylfuran and Ethylene to Biobased p-Xylene

The potential of amorphous silica-alumina (ASA) to substitute zeolites (HBeta-25) for the synthesis of p-xylene via Diels-Alder cycloaddition (DAC) of ethylene to 2,5-dimethylfuran (2,5-DMF) is investigated. ASA were prepared via homogeneous deposition-precipitation of Al on SiO2. ASA shows good yields of p-xylene (20-25 % after 18 hours) compared to bare silica and gamma-alumina. Bronsted acid sites (BAS) were identified as the active sites for the DAC reaction. The catalytic performance correlated strongly with the BAS concentration. Increasing the acidity of ASA is, however, limited by formation of agglomerated alumina-type clusters at higher Al3+ content. While HBeta-25 zeolite shows initially a slightly higher performance in terms of p-xylene yield, ASA is the better catalyst upon calcination-regeneration of the used catalyst. These results furthermore confirm that confinement in zeolite micropores is not a prerequisite for the DAC reaction between 2,5-DMF and ethylene.

Automated summary

This study investigates the potential of amorphous silica-alumina (ASA) as a substitute for zeolites in the synthesis of p-xylene through Diels-Alder cycloaddition (DAC) of ethylene to 2,5-dimethylfuran (2,5-DMF). ASA shows promising yields of p-xylene and Bronsted acid sites (BAS) are identified as the active sites for the reaction. Additionally, ASA proves to be a more effective catalyst than zeolite after calcination-regeneration treatment.