Selectivity tuning of alumina-supported bimetallic transition metal catalysts in a toluene/methylcyclohexane LOHC system for hydrogen energy storage

To develop cost-effective, efficient, and selective catalysts for hydrogen storage in the toluene–methylcyclohexane (TOL–MCH) liquid organic hydrogen carrier (LOHC) system, especially for the challenging dehydrogenation of MCH (the hydrogen release step), a series of indium-modified Ni/γ-Al 2 O 3 catalysts with different metal compositions were prepared and examined. The catalysts were characterized using various methods, including X-ray powder diffraction, temperature-programmed hydrogen reduction (H 2 -TPR), X-ray photoelectron spectroscopy, CO pulse chemisorption, FT-IR spectroscopy to investigate adsorbed CO, high-resolution TEM, and Raman spectroscopy. The Ni-based catalysts exhibited high activity and selectivity (>99%) in TOL hydrogenation at 125 °C and 31 bar. However, under more severe conditions in MCH dehydrogenation at 400 °C, 1 bar, and WHSV= 1 g MCH /(g cat. ⋅h), the monometallic Ni catalyst exhibited low TOL selectivity (<50%) and experienced rapid activity loss due to significant coke deposition. Conversely, the bimetallic Ni-In catalysts, particularly the one with an optimal composition, demonstrated high TOL selectivity (>95%) and a high conversion level (∼85%) under the same reaction conditions with minimal activity loss during the catalytic run. The high TOL selectivity and stability of the Ni-In catalysts were related to the formation of indium-modified nickel domains and/or Ni-In intermetallic particles, which isolated most of the surface Ni atoms. This limited the formation of pure Ni domains, which are likely responsible for the undesired hydrodemethylation reaction and other side reactions that lead to coke formation and deactivation.