Supported atomically dispersed Rh catalysts exhibit distinct activity and selectivity compared to supported Rh nanoparticles for a wide range of chemistries involving CO as a reactant, including water gas shift, NO reduction by CO, alkene hydroformylation, and the selective conversion of CH4 to valuable liquid C1 and C2 oxygenate. A commonality among these chemistries is the poisoning, or occupation, of the Rh active site by CO ligands, which forms stable Rh dicarbonyls, Rh(CO)2. CO desorption from Rh(CO)2 to form Rh(CO) and enable the adsorption of additional reactants is a consistent kinetically relevant elementary step. This results in: (a) challenges in spectroscopic characterization of the fast elementary steps occurring subsequent to CO desorption and (b) the examination of various approaches for destabilizing CO on Rh including controlling reactant concentrations and tuning the local Rh coordination. Here, we highlight the use of UV photolysis of the Rh-CO bond in Rh(CO)2 at low temperature to produce highly reactive and undercoordinated Rh monocarbonyl, Rh(CO), active sites. Through the use of in-situ FTIR and X-ray absorption spectroscopy, we demonstrate that the Rh(CO) species produced via low temperature photolysis are consistent with Rh(CO) species produced at elevated processes through thermal mechanisms. Based on this, we utilize low temperature photolysis to interrogate the mechanisms of reactions, such as the selective oxidation of CH4 to acetic acid and NO reduction by CO, at cryogenic temperature where reactive intermediates evolve on slow enough timescales for observation by in-situ FTIR. Furthermore, we will show that UV illumination can promote the rates of catalytic chemistries that are limited by CO desorption from atomically dispersed Rh(CO)2. This work highlights the interesting potential role of photolysis in promoting and understanding catalytic chemistry by atomically dispersed metal active sites.

Award Address (Ipatieff Prize sponsored by the Ipatieff Trust Fund). Photolysis for probing reaction mechanisms and promoting rates on atomically dispersed Rh catalysts

Fall 2022 abstracts, posters, and presentations will launch in mid-September.

ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.