Rh nanoclusters encaged in hollow mesoporous silica nanoreactors with enhanced catalytic performance for phenol selective hydrogenation

Here, we report the synthesis of Rh nanoclusters (similar to 0.8 nm) encapsulated in hollow mesoporous silica nanoreactors (Rh@HMSNs) for phenol selective hydrogenation. Specifically, triple ligands were used to bind Rh3+ ions to form negatively charged coordination complex network, which further combines by electrostatic attraction with positively charged diblock copolymers to obtain Rh3+ ions bound polymer micelles. Following silica deposition onto micelles, calcination and H-2 reduction result in hollow mesoporous silica nanoreactors and residence of Rh nanoclusters close to their hollow cavities. Relative to the control silica supported Rh catalysts, the obtained Rh@HMSNs show significantly enhanced catalytic activity, cyclohexanol selectivity and stability for phenol hydrogenation. By DFT theoretic calculations and comparison of control experiments, the performance enhancement of Rh@HMSNs is ascribed to their unique nanostructures, where the small size of Rh nanoclusters increases the cyclohexanol selectivity by suppressing the formation of cyclohexanone, and the residence of Rh nanoclusters close to hollow cavities enhances their thermal and catalytic stability.