Enhanced ruthenium utilization via succinamic acid-functionalized SiO₂ supports for efficient hydrogen storage in toluene-based LOHC systems

Abstract

Toluene is a representative liquid organic hydrogen carrier (LOHC) with favorable thermodynamic and physical properties for reversible hydrogen storage. In this study, we report the synthesis of Ru-based catalysts supported on SiO₂ materials (SBA-15 and commercial SiO₂), surface-functionalized with succinamic acid to improve nanoparticle anchoring and metal utilization. Characterization confirmed the successful incorporation of carboxylic groups via a ring-opening grafting approach, leading to significant enhancements in Ru dispersion and stabilization. The Ru/SBA15-AC catalyst exhibited a narrow particle size distribution centered at 4 nm and a dispersion of 32 %. Catalytic tests revealed high activity and total toluene hydrogenation, with the Ru/SBA15-AC system achieving, after 3 h of reaction, a hydrogen storage capacity of 5.2 wt% and a TOF of 639 min⁻¹—outperforming most reported Ru-based catalysts under comparable conditions. Apparent activation energies (Eₐₐ) for all catalysts, determined from Arrhenius analysis, revealed that Ru/SBA15-AC exhibited the lowest value (41 kJ mol⁻¹). The combination of mesoporosity and carboxylic functionality appears to synergistically promote both Ru dispersion and the stabilization of highly active Ru species, which is reflected in the lower energy barrier for hydrogenation. Notably, the catalyst retained its structural integrity and activity over ten consecutive reaction cycles, as confirmed by post-reaction HR-TEM and recyclability assays. In addition to toluene, the Ru/SBA15-AC catalyst also demonstrated effective hydrogenation of other relevant LOHCs, including naphthalene, 2-methylindole, and 9-ethylcarbazole, highlighting its versatility across structurally diverse hydrogen carriers. While a complete LOHC cycle requires both hydrogenation and dehydrogenation steps, this work focused on the hydrogenation half-cycle to elucidate the role of support functionalization on catalyst efficiency and durability.These findings demonstrate that succinamic acid-modified SiO₂ supports represent a robust platform for designing recyclable, atom-efficient Ru catalysts, offering a promising pathway for practical hydrogen storage in LOHC systems.