Liquid organic hydrogen carrier (LOHC) systems provide a promising alternative to pressurized gas and liquid hydrogen storage technologies due to their high volumetric storage capacities and straightforward adaptation to existing infrastructure. Here, we evaluate the performance of various molecular and heterogenized Ru, Mn, and Fe catalysts for the reversible (de)hydrogenation of 1,4-butanediol (BDO) to γ-butyrolactone (GBL). Two Mn catalysts, Mn-MACHO(Ph) (1) and Mn-MACHO(iPr)BH4 (2-BH4), were found to maintain catalytic activity for hydrogen production comparable to the Ru analogs, with greater than 98% conversion of 1,4-butanediol and quantitative hydrogen production. Conversely, Fe-MACHO(iPr)-BH4 (3) was found to have incomplete dehydrogenation of BDO and a low GBL yield of 58%. To assess the viability of utilizing heterogenized molecular catalysts for 1,4-butanediol (de)hydrogenation, molecular catalysts, Mn-MACHO(Ph), Ru-MACHO(Ph), and Ru-9, were polymerized to form Mn-MACHO-Poly, Ru-MACHO-Poly, and Ru-9-Poly, respectively, and their catalytic activity was evaluated. These experiments reveal that Ru-MACHO-Poly is an efficient dehydrogenation catalyst with 99% conversion and a hydrogen yield of 96%. Ru-MACHO-Poly also displayed excellent activity for the reverse reaction, hydrogenating GBL to BDO with 98% conversion according to quantitative NMR analysis. Top-performing catalysts, Ru-MACHO, Ru-MACHO-Poly, and 2-BH4, were assessed under neat conditions using Sieverts measurements, confirming their high catalytic efficiency. Overall, these molecular and heterogenized catalysts demonstrate robust and reversible hydrogen cycling performance, highlighting the potential of polyalcohol-based LOHC systems.
Torquato et al. (Thu,) studied this question.