Bifunctional hydroformylation on heterogeneous Rh-WO pair site catalysts.

Metal-catalysed reactions are often hypothesized to proceed on bifunctional active sites, whereby colocalized reactive species facilitate distinct elementary steps in a catalytic cycle. Bifunctional active sites have been established on homogeneous binuclear organometallic catalysts. Empirical evidence exists for bifunctional active sites on supported metal catalysts, for example, at metal-oxide support interfaces. However, elucidating bifunctional reaction mechanisms on supported metal catalysts is challenging due to the distribution of potential active-site structures, their dynamic reconstruction and required non-mean-field kinetic descriptions. We overcome these limitations by synthesizing supported, atomically dispersed rhodium-tungsten oxide (Rh-WO) pair site catalysts. The relative simplicity of the pair site structure and sufficient description by mean-field modelling enable correlation of the experimental kinetics with first principles-based microkinetic simulations. The Rh-WO pair sites catalyse ethylene hydroformylation through a bifunctional mechanism involving Rh-assisted WO reduction, transfer of ethylene from WO to Rh and H dissociation at the Rh-WO interface. The pair sites exhibited >95% selectivity at a product formation rate of 0.1 g cm h in gas-phase ethylene hydroformylation. Our results demonstrate that oxide-supported pair sites can enable bifunctional reaction mechanisms with high activity and selectivity for reactions that are performed in industry using homogeneous catalysts.