Ionic mesoporous polyamides enable highly dispersed ultrafine Ru nanoparticles: a synergistic stabilization effect and remarkable efficiency in levulinic acid conversion into γ-valerolactone

Abstract

Hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) is one of the most significant biomass platform molecule conversions in terms of producing renewable chemicals and fuels, but the design of highly active and stable heterogeneous catalysts is still challenging. Herein, versatile ionic mesoporous polyamides (iMPAs) were straightforwardly constructed through the amidation of task-specific carboxyl-functionalized pyridinium salts with aromatic amines. The synergistic effect of the amide groups and ionic moieties in the repeating unit of the porous ionic polymeric skeleton provided satisfactory stabilization towards ruthenium (Ru) species and thus enabled the formation of ultra-fine and highly dispersed Ru nanoparticles (NPs) with an average size of ∼2 nm at a high loading level (5.68 wt%, comparable to commercial Ru/C). These Ru NPs effectively catalyzed the conversion of LA into GVL, attributable to the formation of robust Ru NPs and advantageous surface wettability of iMPAs. High yield/selectivity and stable reusability were attained under mild conditions and the efficiency was further highlighted by a record-high space time yield (STY) of 411 g_GVL g_catalyst⁻¹ h⁻¹ in the initial stage (∼30% conversion) at a large LA/Ru ratio (17 500). This work reveals a promising strategy towards the synthesis of active and stable metal NPs via rational monomer design and porosity control of multifunctional ionic porous polymers.