Dehydrogenation of 1-Methyldecalin as a Liquid Organic Hydrogen Carrier: Effect of Isomer Composition on Catalyst Performance and Stability

Abstract Liquid organic hydrogen carriers (LOHCs) represent a safe and cost-effective resource for hydrogen storage due to reversible hydrogenation/dehydrogenation cycles. Although scarcely studied, the 1-methylnaphthalene/1-methyldecalin (1-MN/1-MD) pair could be an attractive LOHC due to its physical properties and because it can be obtained from waste streams of the carbochemical industry. However, 1-MD dehydrogenation is strongly affected by its stereoisomeric composition, as cis- and trans-isomers exhibit different reactivities and can undergo concurrent isomerization. In this work, the influence of individual 1-MD stereoisomers on dehydrogenation performance was systematically investigated using two feeds enriched in either cis- or trans-isomers. Pd- and Pt-based catalysts supported on alumina and activated carbon were evaluated, and the effect of temperature (250–400 °C) was studied over the most active catalyst, Pt/Al2O3. Based on the experimental data, we hypothesized that trans-isomers promoted catalyst deactivation and coke formation, whereas cis-isomers enhanced dehydrogenation activity. This effect is also believed to influence the formation of intermediate products. Specifically, 1-methyltetralin, which is generated mainly from cis-isomers, readily dehydrogenates to 1-methylnaphthalene (1-MN), whereas 5-methyltetralin, formed preferentially from trans-isomers, appears to promote catalyst deactivation.