Insights into the glucose isomerization mechanism of Al-hydrochar catalyst probed by Al-oxide species transformation

Abstract

This study proposed one-pot hydrothermal carbonization as an eco-friendly and facile approach to engineer aluminum (Al)-hydrochar catalyst for effective glucose isomerization to fructose. Different hydrothermal temperatures for in-situ loading Al-oxide species on hydrochar support and the catalytic active sites modification via calcination in oxygen were investigated and the transformations mechanism of Al-oxide species at varying hydrothermal and calcination temperatures was explored. The results showed that nano-size Al-containing species were uniformly loaded on carbon support via hydrothermal carbonization below 200 °C and the prepared Al loaded hydrochar at 180 °C after calcination at 300 °C yielded 39.5% fructose with 92.6% selectivity in acetone/water reaction medium at 160 °C for 20 min. The catalysts prepared at a hydrothermal temperature below 200 °C facilitated the formation of an amorphous Al-containing structure less than 0.5 nm, and calcination at 300 °C under aerobic conditions formed the effective active sites. This sustainable and straightforward route of loading nano-metal Al-containing species on hydrochar support as glucose to fructose isomerization catalyst has high potential in biorefining.