Enhancing Energy Efficiency in Saccharide-HMF Conversion with Core/shell Structured Microwave Responsive Catalysts

Core/shell structured microwave responsive catalysts with carbon nanotube (CNT) core and acidified TiO₂ shell were synthesized in this work for catalytic conversion of saccharide to 5-hydroxymethylfurfural (HMF). The microstructures and surface properties of these hybrid composites were carefully characterized. With such a structure of inner microwave absorber and outer catalyst shell, the heat generated at the core area by microwave radiation can be translated to the shell catalyst directly. Such localized heating allows maximum heat utilization in the reaction and enhances the energy efficiency of the catalytic reaction. The energy efficiency of HMF formation reaches up to 4.2 mol·kJ^-1·L^-1 by using CNT/TiO₂ catalyst, which is six-times higher compared to pure TiO₂. The reaction can be completed within 30 min. The effects of TiO₂ shell thickness, annealing temperature, catalyst concentration, and microwave power on the saccharide conversion and HMF yield were systematically investigated. These catalysts have been demonstrated effective in the hydrolysis conversion of various saccharides, such as fructose, glucose, and sucrose.