Quantitative investigation on microwave-accelerated fructose conversion via fluorescent thermometry

Abstract

The use of microwave (MW) is promising for resolving energy-intensive problems that occur in carbohydrate bioconversion. To quantitatively investigate the mechanism of MW-accelerated reactions, the present study designs three carbon-based catalysts with distinct dielectric loss values (namely, SCS-SO3H, SCS-800-SO3H, MHCS-800-SO3H) for fructose hydrolysis. A fluorescence thermometer (Eu/Tb metal organic complex) was loaded on catalysts for in situ measurement of their localized temperature during MW heating. The combination of fluorescence experiments and theoretical modelling predicts that the temperature gradient between SCS-800-SO3H particles and bulk solvents reaches 26.10°C, which causes an 8.13-fold increase in reaction rate constants. Surprisingly, this speedup value is increased to 28.57 because of the thermal gradient up to 62.10°C when using MHCS-800-SO3H. In contrast, the MW-transparent SCS-SO3H exhibits no significant increase in the reaction rate. The quantitative elucidation of dominant roles of hot spots is promising for guiding the development of high-efficiency catalysts for MW-assisted heterogeneous reactions.