Enhanced Proximity of Rh1,2‐Rhn Ensembles Encaged in UiO‐67 Boosting Catalytic Conversion of Syngas to Oxygenates

Maintaining high conversion under the premise of high oxygenates selectivity in syngas conversion is important but a formidable challenge in Rh catalysis. Monometallic Rh catalysts provide poor oxygenate conversion efficiency, and efforts have been focused on constructing adjacent polymetallic sites; however, the one-pass yields of C₂₊ oxygenates over the reported Rh-based catalysts were mostly <20 %. In this study, we constructed a monometallic Rh catalyst encapsulated in UiO-67 (Rh/UiO-67) with enhanced proximity to dual-site Rh_1,2-Rh_n ensembles. Unexpectedly, this catalyst exhibited high efficacy for oxygenate synthesis from syngas, giving a high oxygenate selectivity of 72.0 % with a remarkable CO conversion of 50.4 %, and the one-pass yield of C₂₊ oxygenates exceeded 25 %. The state-of-the-art characterizations further revealed the spontaneous formation of an ensemble of Rh single atoms/dimers (Rh_1,2) in the proximity of ultrasmall Rh clusters (Rh_n) confined within the nanocavity of UiO-67, providing adjacent Rh⁺-Rh⁰ dual sites dynamically during the reaction that promote the relay of the undissociated CHO species to the CH_x species. Thus, our results open a new route for designing highly efficient Rh catalysts for the conversion of syngas to oxygenates by precisely tuning the ensemble and proximity of the dual active sites in a confined space.