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

The influence of calcination temperature on ZrO₂ and its catalytic activity in glucose conversion was studied in this research. It shows that different structure of ZrO₂ can be obtained by tuning calcination temperature, which results in the various surface catalytic properties. Quantitative evaluation of acidity by NH₃-TPD and solid-state NMR spectroscopy shows that ZrO₂ calcined at 300 °C, which is in amorphous state and has a higher BET surface area, possesses more Brønsted and Lewis acid sites than ZrO₂ samples calcined at other temperatures. Amorphous ZrO₂ 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 ZrO₂. There is a distinct decrease in Brønsted acid sites, along with a decrease of the total number of acid sites in ZrO₂ as calcination temperature increases. At the same time, a new type of Lewis acid appears at a downfield shift, resulting in different reaction rates.