Research progress on carbon-based catalysts for catalytic dehydrogenation of liquid organic hydrogen carriers

Hydrogen energy is a widely available, flexible and efficient secondary energy source, and it is also an important energy medium. The development of low-cost, high-density hydrogen storage technology is a significant issue for the industrial application of hydrogen energy. Liquid organic hydrogen storage has attracted extensive attention due to advantages such as high mass hydrogen storage density, safe storage and transportation, as well as ease of long-distance transportation. However, compared with the relatively mature hydrogenation process, the dehydrogenation of liquid organic hydrogen carriers (LOHCs) still suffers from high reaction temperature and low efficiency. The key to solving these problems is the development of efficient dehydrogenation catalysts. In recent years, carbon-based catalysts have shown excellent reaction performance in the dehydrogenation of LOHCs due to their advantages of high dispersion of active components, tunable composition structure and surface physicochemical properties, and outstanding electrical and thermal conductivity, etc. In this review, we initially analyze the thermodynamics and kinetics of dehydrogenation, as well as the physicochemical properties of LOHCs, including cyclohexane, methylcyclohexane, decalin, and perhydro- N -ethylcarbazole. The special features of carbon supports are then outlined in terms of the activated carbon, carbon nanotubes, carbon fibers, and reduced graphene oxide. In addition, the structural characteristics, catalytic performance, structure-property relationship, and dehydrogenation mechanism of carbon-supported metal catalysts are summarized and analyzed. Based on this, we point out the main challenges of liquid organic hydrogen storage. Furthermore, future opportunities in this field are envisioned, with an emphasis on the modification and structuration of carbon support, the study of catalytic mechanisms and chemical process intensification. This review summarizes the structural characteristics, catalytic performance, structure-property relationship and catalytic mechanism of carbon-supported metal catalysts for dehydrogenation of liquid organic hydrogen carriers, and provides an outlook on their future opportunities and challenges.