Surface intermediates steer the pathways of CO2 hydrogenation on Pt/γ-Al2O3: Importance of the metal-support interface

A variety of adsorbed intermediates have been extensively assigned during CO2 hydrogenation on Pt/γ-Al2O3. However, the surface sites where the surface species reside have not been well resolved, which are extremely important to depict the reaction pathways of CO2 hydrogenation. In the current work, surface species adsorbed on three regions were distinguished by in situ diffuse-reflectance infrared Fourier transform spectroscopy, i.e., contiguous Pt region of Pt nanoparticle, interfacial Ptint-O-Alint region between Pt nanoparticle and γ-Al2O3, and surface region of γ-Al2O3 away from Pt nanoparticle. The dynamics of adsorbed H species, carbonyl species, bicarbonates, formate species, and adsorbed CO2, were identified at different sites, proving that the reaction occurs at the Pt/γ-Al2O3 interface. We found that only the C-containing species at the Pt perimeter are directly active intermediates for the reaction. Such spatial analysis bridges the gap between the hydrogen activation and CO2 activation, providing a deep understanding of CO2 hydrogenation. In addition, the interface structure with oxygen vacancy is important for CO2 activation, driving the reaction through carboxylate (*HOCO) pathway to form CO at the interface rather than formate (*HCOO) pathway and then be hydrogenated at the Pt surface.