Bimetallic Rh–M/CeO₂ Catalysts for Reversible Hydrogenation–Dehydrogenation in Liquid Organic Hydrogen Carriers (LOHCs)

Liquid organic hydrogen carriers (LOHCs) demonstrate a distinct advantage over alternative hydrogen storage methods, owing to their high hydrogen storage capacity and well-established infrastructure. Nonetheless, the advancement of an efficient catalytic reversible (de)hydrogenation employing a singular catalyst is highly desirable. In this context, 0.5 wt.% Rh impregnated with a series of transition metals (M = Mn, Co, Fe, Ni) by 10 wt.% on cerium oxide (CeO₂) support (0.5%Rh–10%M/CeO₂) has been prepared for the hydrogenation of toluene (TOL) and dehydrogenation of methylcyclohexane (MCH) to complete the LOHCs cycle. Synthesized catalysts have been characterized by XRD, SEM, TEM, EDS, and mapping. XRD reveals the crystallinity of the 0.5%Rh–10%Mn/CeO₂ catalyst. Mapping demonstrates the uniform dispersion of metal on the CeO₂ support, and strong metal–support interactions are confirmed by temperature-programmed desorption studies (H₂-TPR). The catalytic experiments showed that 0.5%Rh–10%Mn/CeO₂ catalyst exhibited the highest performance toward the hydrogenation of toluene (Tol), achieving 84% conversion with >99% methylcyclohexane (MCH) selectivity at 80°C, under 40 bars of hydrogen pressure using 10 mg catalyst loading. The activity trend with different transition metal loadings is established as follows: 0.5%Rh–10%Mn/CeO₂ > 0.5%Rh/CeO₂ > 0.5%Rh–10%Co/CeO₂ > 0.5%Rh–10%Ni/CeO₂ > 0.5%Rh–10%Fe/CeO₂, highlighting the synergistic effect of bimetallic components (Rh–Mn) in improving hydrogenation performance. Furthermore, the dehydrogenation of MCH has been conducted using a 0.5%Rh–10%Mn/CeO₂ catalyst at a temperature of 200°C for 24 h, resulting in an 80% conversion of MCH to TOL. 0.5%Rh–10%Mn/CeO₂ catalyst maintained its stability for five consecutive cycles in both hydrogenation and dehydrogenation experiments without significant loss in its activity.