Spontaneous Dissociation of CO2 to CO on Defective Surface of Cu(I)/TiO2-x Nanoparticles at Room Temperature

The activation of CO2 on defective surface of Cu(I)/TiO2-x has been studied using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). It was demonstrated that CO2-, species, generated upon an electron attachment to CO2, are spontaneously dissociated into CO even in the dark on a partially oxygen depleted Cu(I)/TiO2-x surface prepared by thermal annealing in an inert environment. The formation of CO bound on Cu+ sites was identified in the DRIFT spectra, and isotopic carbon-labeling experiments confirmed that the produced CO was derived from CO2. The spontaneous dissociation of CO2- in the dark is to a large extent associated with the surface oxygen vacancies that provide not only the electronic charge (i.e., formation of Ti3+) but also the sites for the adsorption of oxygen atoms from CO2. The surface Cu+ species may facilitate destabilizing adsorbed CO2- and enhance its subsequent dissociation. to CO. The defective surface is much more active than defect free surface; the healed oxygen vacancies after CO2 reduction can be easily regenerated via inert gas annealing at a moderate temperature (i.e., 300 degrees C). Compared with in the dark, CO2 activation and dissociation under photoillumination is remarkably improved, possibly because of sustained electron supply and partial regeneration of surface oxygen vacancy induced by irradiation. The results from DRIFTS analysis were verified by the measurement of catalytic activity using gas chromatography. These findings are important to advancing the understanding in the chemistry of CO2 adsorption and photocatalytic reduction on the surface of metal oxide catalysts.