Preparation of noble metal catalysts and their catalytic hydrogenation performance for liquid organic hydrogen carriers

Hydrogen, as a clean renewable energy with a high calorific value, exhibits broad application prospects in transportation, chemical engineering and aerospace. To achieve energy security and carbon neutrality goals, the development of renewable hydrogen and its storage and transportation technology have become a crucial aspect. Liquid Organic Hydrogen Storage （LOHC） has emerged as a significant pathway for green hydrogen storage and transportation due to its high hydrogen storage capacity, favorable thermodynamic properties, and compatibility with existing fuel infrastructure. However, the efficiency of its hydrogenation or dehydrogenation processes is highly dependent on catalyst performance. Existing research primarily focuses on the development of single noble metal catalysts. Nevertheless, disparities in preparation methods, support characteristics, and reaction conditions have led to difficulties in direct cross-comparison of activity data, hindering the deep analysis of structure-activity relationships and the rational design of highly efficient catalysts. Addressing the demand for efficient hydrogenation of organic liquid carriers, this study synthesized Ru/Al₂O₃, Rh/Al₂O₃, Pd/Al₂O₃, and Pt/Al₂O₃ noble metal hydrogenation catalysts using the excess impregnation method in parallel, with monobenzyltoluene （H0-MBT） and dibenzyltoluene （H0-DBT） as reaction substrates. The physic and chemical properties were systematically characterized using TEM, H₂-TPR, N₂ physisorption-desorption, XRD, and XPS. Subsequently, their catalytic hydrogenation performance was comparatively investigated. Results indicated that Pt/Al₂O₃, attributed to the strong anchoring effect of pentacoordinate Al³⁺ sites on the γ-Al₂O₃ surface, exhibited the best metal dispersion and the smallest average particle size （<2 nm）. In catalytic hydrogenation reactions, Pt/Al₂O₃ demonstrated superior activity, achieving complete hydrogenation in 80 min for H0-MBT and 120 min for H0-DBT, significantly outperforming other precious metal catalysts. Under optimized conditions of 0.5% Pt loading, 5 MPa H₂ and 600 r/min, the optimal reaction temperatures for H0-MBT and H0-DBT hydrogenation were found to be 160 ℃ and 180 ℃, respectively. The design of highly efficient LOHC catalysts and the optimization of related processes are supported by fundamental data provided by this research.