Glucose conversion to 5-hydroxymethylfurfural on zirconia: Tuning surface sites by calcination temperatures

Abstract

• Different structures of ZrO 2 with various surface catalytic properties are synthesized. • ZrO 2 calcined at 300 °C possesses more Brønsted and Lewis acid sites than other ZrO 2 samples. • Increasing calcination temperature will decrease total acidity and create new Lewis acid sites. • ZrO 2 can convert nearly 100% of glucose with an HMF selectivity of about 40%. The influence of calcination temperature on ZrO 2 and its catalytic activity in glucose conversion was studied in this research. It shows that different structure of ZrO 2 can be obtained by tuning calcination temperature, which results in the various surface catalytic properties. Quantitative evaluation of acidity by NH 3 -TPD and solid-state NMR spectroscopy shows that ZrO 2 calcined at 300 °C, which is in amorphous state and has a higher BET surface area, possesses more Brønsted and Lewis acid sites than ZrO 2 samples calcined at other temperatures. Amorphous ZrO 2 shows a better catalytic performance in glucose conversion, nearly 100% glucose conversion with an HMF selectivity of about 40%. Increasing calcination temperature leads to a result of sintering, crystallizing, and pore collapsing of ZrO 2 . There is a distinct decrease in Brønsted acid sites, along with a decrease of the total number of acid sites in ZrO 2 as calcination temperature increases. At the same time, a new type of Lewis acid appears at a downfield shift, resulting in different reaction rates.