Mesoporous Acidic SiO2-Al2O3 Support Boosts Nickel Hydrogenation Catalysis for H2 Storage in Aromatic LOHC Compounds

Abstract

Transition-metal catalysts are essential to realize a liquid organic hydrogen carrier (LOHC) system based on reversible hydrogenation and dehydrogenation. To attain com-parable hydrogenation activity to noble metal catalysts mainly used so far, catalyst constituents need to be blended together toward improved adsorption and kinetics. For nickel catalysis in the hydrogenation of aromatic LOHC (monobenzyltoluene), meso-porous SiO2-Al2O3 (MSA) supports are herein prepared by solvent-deficient precipitation using aluminum isopropoxide and alkyltriethoxysilane (CnTES, in which n = 3, 8, and 18). Although Ni particle sizes are similar in all of the prepared catalysts, the hydrogenation activity of Ni/MSA_CnTES is in a volcano-shaped relationship with the length of the alkyl substituent of CnTES, where Ni/MSA_C8TES shows 2-fold superior activity to the Ni catalyst supported on mesoporous alumina. The observed volcano trend is attributed to the adsorption of aromatic substrates affected by Lewis acidity and, more significantly, the adsorption of hydrogen on the Ni species located in the vicinity of the mixed SiO2-Al2O3 domains having Bronsted acidic protons for promoted H2 spillover. Moreover, the mesopores of MSA_CnTES contribute to the facile transport of the reactant and the product. Therefore, these catalyst characteristics would be well balanced in single Ni catalyst bodies for boosted LOHC hydrogenation performance.