Enhanced Proximity of Rh-Rh 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 C 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-Rh 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 C oxygenates exceeded 25 %. The state-of-the-art characterizations further revealed the spontaneous formation of an ensemble of Rh single atoms/dimers (Rh) in the proximity of ultrasmall Rh clusters (Rh) confined within the nanocavity of UiO-67, providing adjacent Rh-Rh dual sites dynamically during the reaction that promote the relay of the undissociated CHO species to the CH 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.