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

Abstract

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 SiO 2 . ASA shows good yields of pxylene (20-25 % after 18 hours) compared to bare silica and γalumina. Brønsted 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 Al 3 + content. While HBeta-25 zeolite shows initially a slightly higher performance in terms of p-xylene yield, ASA is the better catalyst upon calcinationregeneration 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.

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

“…aConcentration of the total Brønsted (1545 cm −1 ) and Lewis (1455 cm −1 ) was obtained after evacuation of pyridine at 150 °C, while the concentration of strong Brønsted was determined after evacuation at 400 °C.bAmount of Brønsted acid sites obtained after peak fitting of the CO saturated sample.cIR band position of the CO–OH complex.dData were taken from ref. 24.…”

“…Although not investigated in this work, previous studies have shown that ASA prepared by the grafting of Al shows higher stability in the DAC reaction compared to the zeolite benchmark. 24 This has been linked to the absence of Al leaching from the ASA surface and the poor structural integrity of the HBeta crystal upon consecutive reuse. 24,33…”

“…An ordered mesoporous silica was synthesized using the surfactant 1,2-dimethyl-3-hexadecyl-1H-imidazol-3-ium bromide (C 16 IMZ). 37 24,25,33,38 For this purpose, a suspension containing OMS-C 16 IMZ (30 g L −1 ), 0.76 M urea (Sigma Aldrich, 99.5%), and the desired amount of Al(NO 3 ) 3 •9H 2 O (Merck, purity 99%) was made. The temperature of the mixture was raised to 90 °C while monitoring the pH.…”

“…d Data were taken from ref. 24. Catalysis Science & Technology Paper formation of alumina domains at higher Al concentrations.…”

“…24 This has been linked to the absence of Al leaching from the ASA surface and the poor structural integrity of the HBeta crystal upon consecutive reuse. 24,33 Conclusions A set of ASA samples prepared by different methods including templated synthesis to direct hydrothermal synthesis (OMS-10), homogeneous deposition-precipitation of aluminium (OMS-HDP-10 and SBA-15-HDP-10), and flame spray pyrolysis (ASA-FSP-10 and ASA-FSP-1) were prepared to investigate the effect of surface area and the Al location on the DAC reaction of 2,5-DMF with ethylene to p-xylene. Al grafting by HDP on mesoporous silica such as OMS and SBA-15 with high surface areas results in ASA with the highest content of BAS.…”