Hydrogen Separation from Gas Mixtures by Its Chemical Storage via Hydrogenation of Aromatic Compounds over Dispersed Ni–Mo–Sulfide Catalysts

The study investigated hydrogenation of aromatics as liquid organic hydrogen carriers over unsupported NiMoS catalysts synthesized in situ by dispersion followed by high-temperature decomposition/sulfidation of oil-soluble precursors of the active component in a hydrocarbon medium. The separation of hydrogen from gas mixtures via its chemical storage was demonstrated. The hydrogenation of naphthalene, its monomethylated derivatives, and anthracene was investigated with various component ratios in the gas mixtures. Specifically, the effects of temperature, pressure, reaction time, and the presence of water under water gas shift reaction (WGSR) conditions on the substrate conversion and product selectivity were evaluated. When carrying out the process in syngas atmosphere (CO : H 2 = 1 : 1) at 340°C and 5 MPa, the aromatics conversion and the hydrogen saturation were found to decrease in the following order: anthracene > 2-methylnaphthalene ≈ naphthalene >> 1-methylnaphthalene. In addition to steric hindrances in the sorption of substrate molecules (due to the presence of substituents in the benzene ring), the structure of conformational isomers of intermediate molecules has a major effect on the hydrogenation reaction rate. Dispersed NiMoS catalysts were found to be active in the hydrogenation of 2-methylnaphthalene, achieving at least 90% conversion to the corresponding tetralins (with the 6-methyltetralin to 2-methyltetralin ratio ranging between 1.5 : 1 and 1.7 : 1) at 320–360ºC and a total pressure of 5 MPa with 25–50 vol % carbon monoxide and methane in the gas mixture. Under WGSR conditions (10 wt % water, CO : H 2 = 1 : 1, total pressure 5 MPa), at least 1.2 wt % sulfur as a precursor of the sulfiding agent is needed (at molybdenum content of 0.06 wt %) to ensure in situ regeneration of the catalyst and its transition into the active sulfide form.