Valorization of corn stover into furfural and levulinic acid over SAPO-18 zeolites: Effect of Brønsted to Lewis acid sites ratios.

• SAPO-18 zeolites with Brønsted and Lewis acid sites were used as bifunctional catalyst. • Brønsted to Lewis acid site ratios were adjusted by modifying the Si/Al ratios. • Lower Brønsted to Lewis acid site ratios enhanced furfural production. • Higher Brønsted to Lewis acid site ratios facilitated levulinic acid formation. • The effect of Brønsted to Lewis acid site ratios on the kinetics was investigated. A one-step process was proposed for valorization of corn stover into furfural and levulinic acid catalyzed by SAPO-18 zeolites. With the aim to produce furfural and levulinic acid, the Brønsted to Lewis acid site ratios of SAPO-18 were modified. The influence of reaction temperature, time and the ratios of Brønsted to Lewis acid site on the valorization of corn stover were investigated. At the fixed catalyst concentration of 20 g/L, a furfural yield of 95.1% was observed at 205 °C for 40 min using SAPO-18 with Brønsted to Lewis acid site ratio of 0.11, and a levulinic acid yield of 70.2% achieved at 190 °C for 80 min using SAPO-18 with Brønsted to Lewis acid site ratio of 0.17. The Brønsted to Lewis acid site ratios of SAPO-18 were adjusted by altering the framework Si/Al ratio of SAPO-18. The SAPO-18 with lower Brønsted to Lewis acid site ratios showed higher activity for furfural production from corn stover and that with higher ratios exhibit superior catalytic effect for levulinic acid formation. The kinetic models considering the effect of Brønsted to Lewis acid site ratios agreed with the experiment values well, which provided detailed insights on the conversion of hemicellulose and cellulose fraction of corn stover into furfural and levulinic acid. [ABSTRACT FROM AUTHOR]