A Novel Eutectic Mixture of Biphenyl and Diphenylmethane as a Potential Liquid Organic Hydrogen Carrier: Catalytic Hydrogenation

A novel, liquid-phase hydrogen storage material was produced by mixing biphenyl (C₁₂H₁₀, solid) and diphenylmethane (C₁₃H₁₂, liquid) with a mass ratio (wt %) of 35:65. The eutectic mixture was proved to be liquid at ambient temperature with a viscosity of 3.0 cP at 25 °C and a vapor pressure of 1.4 Pa at 25 °C, which potentially meets the requirements for an efficient hydrogen storage system. A theoretical study using COSMO-RS method further confirms that an optimum composition of biphenyl and diphenylmethane for the formation of eutectic mixture is 37:63 by mass, which is very close to the composition found experimentally. The eutectic mixture exhibited a superior activity for hydrogenation reactions conducted at 120 °C under 50 bar of H₂ pressure in the presence of a Ru (5 wt %)/Al₂O₃ catalyst. Hydrogen uptake of the eutectic mixture tested was close to full conversion, which corresponds to 6.9 wt % and 60.1 g L⁻¹ of gravimetric and volumetric hydrogen storage capacities, respectively.