Diels–Alder Cycloaddition of Biomass-Derived 2,5-Dimethylfuran and Ethylene over Sulfated and Phosphated Metal Oxides for Renewable p-Xylene

Abstract

In this work, sulfated and phosphated metal oxides were studied as catalysts for the Diels–Alder cycloaddition of biomass-derived 2,5-dimethylfuran (DMF) and ethylene to understand the effect of acid strength on the reaction. Four catalysts with varied acidity, namely sulfated SiO2, sulfated TiO2, phosphated SiO2, and phosphated TiO2, were prepared via wet impregnation using sulfuric acid and phosphoric acid as precursors, and their structural and acid properties were examined using X-ray diffraction, Brunauer–Emmett–Teller analysis, Fourier transform infrared spectroscopy, solid state 31P magic angle spinning nuclear magnetic resonance spectroscopy, and temperature programmed desorption of ammonia. The results revealed that the acidity of the catalysts was largely influenced by the type of the acid functional group and the support as well as the calcination temperature. The conversion of DMF and the selectivity toward p-Xylene (PX) were generally correlated with the total acid site density and the acid–metal oxide interaction strength, which in turn affected the acid strength. Overall, phosphated SiO2 and TiO2 calcined at 773 K were identified as the most active and selective catalysts, exhibiting a high PX selectivity of over 70% and DMF conversion of 80% at 523 K after 6 h. The origin of the stability of the highly active phosphated catalysts was also investigated in detail.

Efficient and sustainable production of p-xylene from biomass-derived 2,5-dimethylfuran and ethylene using alkali metal doped phosphotungstic acid catalysts

“…This result is consistent with those of previous reports. 10,24–26 Cs 3 PW showed the highest sum selectivity of PX and CH, but the lowest PX selectivity. This is likely due to the lack of enough acid sites, which limited the dehydration of the CH intermediate to produce PX.…”

“…7,12,13 During the past several years, many homogeneous and heterogeneous acid catalysts have been reported for the conversion of DMF and ethylene to PX. [14][15][16][17] In particular, various heterogeneous catalysts with the advantages of easy recovery and less environment pollution issues, have been explored for this reaction, such as zeolites (H-Y, H-BEA, H-USY, P-Beta, and SAPO-34) 14,[18][19][20][21][22][23] , bulk and supported metal oxides, 11,24,25 sulfonic acid modied mesoporous silica, 10 and supported heteropolyacids. 26 P-Beta was reported to have high catalytic activity, but required a high reaction pressure (6.2 MPa) and long reaction time (24 h).…”