Ru–Ni/Al2O3 bimetallic catalysts with high catalytic activity for N-propylcarbazole hydrogenation

Abstract

The catalytic hydrogenation of liquid organic hydrogen carriers (LOHCs) is one of the key steps towards large-scale applications. The use of a large amount of noble metals in hydrogenation factories would increase the total cost of the LOHC technology. The partial replacement of ruthenium by another transition metal, i.e., Ni is a potentially effective method. The synthesis and characterization of 5 wt% Ru_xNi_5−x/Al₂O₃ (x = 0, 1, 2.5, 4, and 5) bimetallic catalysts and their catalytic performance for the hydrogenation of N-propylcarbazole are reported. All catalysts were prepared by a wet chemistry method using a rapid sodium borohydride reduction of the Ni²⁺ and Ru³⁺ precursors in alkaline solutions. The catalysts were characterized by TEM, XRD, XPS, nitrogen sorption, ICP-OES, H₂-TPD and CO adsorption. The as-prepared 5 wt% Ru_2.5Ni_2.5/Al₂O₃ exhibits the best catalytic activity compared to the as-prepared catalysts with the highest metal dispersion and minimum average particle size of 5.210 nm. The hydrogenation activation energy for 5 wt% Ru_2.5Ni_2.5/Al₂O₃ at 150–180 °C was estimated to be approximately 12.95 kJ mol⁻¹. No obvious degradation was observed after 5 cycles of hydrogenation for the 5 wt% Ru_2.5Ni_2.5/Al₂O₃ catalyst, indicating that the catalyst has applicable stability. The hydrogen spillover has been proved to occur more easily on the Ru–Ni clusters by theoretical calculations.