Encapsulating Ru Nanoclusters for Reductive Imination of Biomass-Based Furfural by Shape-Selective Catalysis

Reductive imination of aldehydes to the corresponding secondary imines, while attractive and promising, remains a big challenge due to consecutive hydrogenation and hydroammonolysis of the in situ formed imine. Herein, we describe a strategy of shape-selective catalysis for the reductive imination of biomass-derived furfural with H₂NOH and H₂ by using Ru nanoclusters confined within the regular micropores of ZSM-5 (Ru@ZSM-5). The Ru@ZSM-5 features a consecutive furfural oxime-hydrogenation and furfurylimine-hydrogenation due to their closed molecular sizes to the pore apertures (5.3 × 5.6 Å) of the ZSM-5. In contrast, the in situ formed secondary imine (4.3 × 11.2 Å) with a large molecular size could not pass through ZSM-5 micropores to reach the active Ru sites, thus remaining unaffected without further hydrogenation and hydroammonolysis. The shape-selectivity of Ru@ZSM-5 is further confirmed by catalyst-passivation and hydrogen-spillover experiments. The Ru@ZSM-5 shows high activity and shape-selectivity with good recyclability and is easily extended to reductive imination of a variety of aldehydes.