Highly active subnanometer Rh clusters derived from Rh-doped SrTiO3 for CO2 reduction

[Display omitted] •Controlled reduction of Rh-doped SrTiO3 leads to subnanometer Rh clusters.•Catalysts synthesized by the doping-segregation method show much higher activities.•Subnanometer Rh clusters provide more sites for the activation of H2 (and C2H6).•Interactions between Rh atoms and support change the binding energies of adsorbates. Sub-nanometer Rh clusters derived from Rh-doped SrTiO3, demonstrated by in-situ X-ray Diffraction (XRD) and X-ray Absorption Fine Structure (XAFS) measurements, are applied as highly active catalysts for CO2 reduction. Compared to the supported Rh/SrTiO3, the catalyst synthesized by a doping-segregation method exhibits a higher space-time yield (STY) to CO with a selectivity of 95% for CO2 reduction by hydrogen; it also shows a higher activity with a larger turnover frequency (TOF) for CO2 reduction by ethane. According to the in-situ diffuse reflectance infrared Fourier transformed spectroscopy (DRIFTS) experiments, the higher CO selectivity for CO2 hydrogenation is attributed to the lower CO binding strength resulted by the strong interactions (e.g., charge transfer) between Rh atoms and the oxide support with surface defects. The superior activity is suggested to be originated from the cooperative effect between the highly dispersed sub-nanometer Rh clusters for efficient dissociation of H2/C2H6 and the reconstructed SrTiO3 with oxygen vacancies for preferential adsorption/activation of CO2. The doping-segregation method provides a unique opportunity to tune the size of active metal clusters and the physicochemical properties of the oxide support, offering the potential for applications in a variety of chemical reactions.