Influence of Support Specific Surface Area and Preparation Method on the Performance of Ru/SiO₂ Catalysts for Biphenyl Hydrogenation to Bicyclohexane

Hydrogen energy is a promising alternative to fossil fuels, yet its storage and transportation remain challenging due to flammability and low density. Liquid organic hydrogen carriers (LOHCs), such as bicyclohexane (BCH) derived from biphenyl (BP) hydrogenation, offer high hydrogen storage density and safety. This study investigates the impacts of support specific surface area (SSA) and preparation methods on the performance of Ru/SiO₂ catalysts in BP hydrogenation to BCH.

Ru/SiO₂ catalysts with varying SSA were prepared using the strong electrostatic adsorption (SEA) and incipient wetness impregnation (IWI) methods with [Ru(NH₃)₆]Cl₃ as the precursor and fumed SiO₂ as the support. The catalysts were characterized using ICP-AES, XRD, N₂ physisorption, H₂-TPR, XPS, TEM, and HAADF-STEM. The catalytic performance was evaluated in a high-pressure autoclave under mild conditions (90 °C, 1.0 MPa H₂, 80 min) with product analysis conducted using GC-MS.

The 1.5 wt.% Ru/SiO₂-SEA (300) catalyst exhibited the best performance, achieving 99.9% BP conversion and BCH selectivity. This catalyst featured smaller Ru nanoparticles (average size 0.91 nm) and stronger metal-support interaction compared to the IWI-prepared catalysts. As the SSA of the SiO₂ support increased, the hydrogenation performance improved.

The research reveals that SiO₂ with high SSA can provide a greater number of active sites, thereby facilitating contact between reactants and the catalyst surface. This enhancement leads to improved catalytic activity and selectivity. Furthermore, the SEA method, which adjusts the solution pH, enables the uniform adsorption of metal ions onto the support surface through electrostatic interactions. This results in smaller Ru nanoparticle sizes and higher dispersion, significantly strengthening the metal-support interaction.

The study highlighted the efficiency of the SEA method in developing the high-performance Ru/SiO₂ catalyst for BP hydrogenation. Higher SSA supports, particularly those prepared via SEA, yielded smaller Ru nanoparticles and enhanced dispersion, resulting in superior catalytic activity and selectivity. These findings offered some critical insights for advancing LOHC technology and hydrogen storage applications.