(558b) Precise Engineering of Oxide Supported Atomically Dispersed Rh Local Environment for Alkene Hydroformylation

There is significant interest in the reactivity of atomically dispersed Pt-group metal atoms (or ions) on oxide supports. These dispersed active sites are comparable to homogeneous catalysts based on the mononuclear active site. Regulating the structural uniformity and controlling the electronic and steric environment of the active site are important for fundamental understanding of the influence of local environment on catalytic properties. It has been reported that the local environment of atomically dispersed catalysts changed by supports and surface coatings influences catalytic properties. However, a synthetic protocol for precise and systematic engineering of local environments of atomically dispersed catalysts, which are stable under reaction conditions, is still missing.

In this talk we demonstrate regulation over the local coordination environment of atomically dispersed Rh on Al₂O₃ through a systematic tuning of interactions between Rh and ReO_x and WO_x acidic sites, or Rh and phosphonic acid anchored hydrocarbons with controlled electronic character. A range of characterization approaches including CO probe molecule FTIR, CO temperature programmed desorption and X-Ray absorption spectroscopy were used to probe how the electronic structure and steric environment of atomically dispersed Rh species were influenced by changes in their local environment. The catalysts were examined for their reactivity in ethylene hydroformylation where it was observed that the electronic and steric modifications induced significant changes in ethylene turn over frequencies (up to 2 orders of magnitude) and reaction selectivity. We will discuss mechanistic interpretations of these findings along with discussing the most effective routes forward for promoting selective alkene hydroformylation reactivity of oxide supported atomically dispersed Rh catalysts.