Constructing Co Cluster Sites for Selective CO<sub>2</sub> Hydrogenation via Phase Segregation from Co-Doped TiO<sub>2</sub> Nanocrystals

Article Constructing Co Cluster Sites for Selective CO2 Hydrogenation via Phase Segregation from Co-Doped TiO2 Nanocrystals Xiangru Wei 1, Yizhen Chen 1, Yulu Zhang 1, Liyue Zhang 1, Lu Ma 2, Matthew M. Yung 3 and Sen Zhang 1,* 1 Department of Chemistry, University of Virginia, Charlottesville, VA 22904, USA 2 National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, NY 11973, USA 3 Bioenergy Science and Technology Directorate, National Renewable Energy Laboratory, Denver West Parkway, Golden, CO 80401, USA * Correspondence: sz3t@virginia.edu Received: 7 November 2024; Revised: 2 January 2025; Accepted: 3 January 2025; Published: 23 January 2025 Abstract: This article presents a Co phase segregation strategy for creating stable Co cluster catalytic sites on TiO2, enabling selective CO2 hydrogenation to CO. Through oxidative calcination, pre-synthesized Co-doped brookite TiO2 nanorods transform into a mixed TiO2 phase, leading to the phase segregation of Co species. The resulting Co clusters, stabilized by strong Co-TiO2 interactions during reductive CO2 hydrogenation, effectively suppress the formation of larger nanoparticles. The undercoordinated sites of these clusters promote a high CO production rate with near-unit selectivity, contrasting with Co nanoparticles, which favor CH4 formation under identical conditions. In-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis indicates that the weakened CO adsorption on Co clusters is key to their enhanced CO selectivity, highlighting this method as a promising approach for efficient CO2 utilization.