Properties of mesoporous Al-SBA-15 from one-pot hydrothermal synthesis with different aluminium precursors and catalytic performances in xylose conversion to furfural

SBA-15 is a stable mesoporous silica with a uniform pore structure but without active catalytic sites. The incorporation of aluminium (Al) into its structure could generate acid sites for catalysis. Here, we report a comparative study of Al-incorporated SBA-15 (Al-SBA-15) by one-pot hydrothermal method from sodium aluminate (SA), aluminium sulfate (AS), and aluminium isopropoxide (AI). All Al-SBA-15 samples have mesoporous characteristics with incorporated Al in the structure, generating acid sites. Despite the similar Si/Al ratios, their total acidities are different, ranging as follows: Al-SBA-15 (SA) < Al-SBA-15 (AS) < Al-SBA-15 (AI). In contrast, the ratio of Al in tetrahedral coordination within the SBA-15 framework (Altet) increases in the opposite trend: Al-SBA-15 (SA) > Al-SBA-15 (AS) > Al-SBA-15 (AI). From catalytic testing, all samples provide better xylose conversions and furfural yields than the pristine SBA-15. The xylose conversions increase with the total acidity, however, the furfural yield depends on the relative ratios of Lewis to Brønsted acid sites. Moreover, lactic acid by-product increases with Al in octahedral coordination (Aloct). The best catalyst is Al-SBA-15 (SA), giving high furfural yield and the fewest by-products. Further investigations on Al-SBA-15 (SA) confirm that the optimum conditions are at 170 °C; for 5 h; and the catalyst loading of 0.10 g.