Pulsed microwave induced super-heating in graphitic carbon domains drives high-efficiency 5-hydroxymethylfurfural synthesis

Abstract

Precise heat delivery to localized active sites for energy-efficient chemical reactions remains a challenge so far since existing strategies for heat transfer rely on the temperature gradient. The coupling of microwave irradiation and microwave-responsive catalysts (MRCs) offers a great opportunity to spatially align heat generation and utilization at targeted positions. In this study, a series of MRCs were fabricated with graphitic carbon in bulk-phase and sulfonation structures at the surface. Raman deconvolution analysis (RDA) and HRTEM revealed that Fe-catalyzed MRC formed loose and curly graphite nanosheets and sulfonic groups grafted onto the graphitized edges, while Co-catalyzed and Ni-catalyzed MRC formed closely packed nanosheets and disordered carbon nanostructures at edges. The structural evolution of carbon altered the dielectric properties of the material and further influenced the microwave response and interfacial reaction. Results indicated that Fe-catalyzed MRCs reached 80 mol% HMF yield in 4 pulsed cycles, reflecting a high energy efficiency (18.5 mmol/KJ·L·g). This outstanding performance stems from the super-heating behavior of MRCs under microwave irradiation, causing the interface reaction temperature to be higher than the bulk temperature. This study clarifies the relationship between carbon nanostructure and microwave response at interfaces and offers practical strategies for enhancing the efficiency of microwave energy utilization in heterogeneous catalysis.