Phase-dependent enhancement for CO2 photocatalytic reduction over CeO2/TiO2 catalysts
CeO2 is a basic promoter for CO2 photoreduction with H2O over TiO2-based catalysts, but there is still a lack of insight into the interaction of CeO2 with different TiO2 polymorphs and its effect on CO2 photoreduction. In this study, pure anatase, brookite, and rutile TiO2 and their respective hybrids with CeO2 were prepared, and their structural properties, optical properties, interfacial interaction and activity for CO2 photoreduction were systematically studied. The addition of CeO2 improved the activity for CO2 photoreduction under simulated sunlight irradiation, but the improvement depends on the phases of the TiO2. X-ray diffraction, macro-Raman spectroscopic and electron paramagnetic resonance measurements confirm the presence of Ti defects at the CeO2–rutile interfaces, implying a relatively strong interaction between CeO2 and rutile, which is beneficial for the interfacial separation of photogenerated charge carriers. As a result, CeO2/rutile shows the best enhancement of CO2 photoreduction among the studied CeO2/TiO2 systems. Moreover, different paramagnetic species were detected in the three TiO2 polymorphs. The O− radical anion in the anatase lattice could be oxidized to produce Ti3+ under UV-light irradiation, whereas the O2− radical anion on the surface of brookite TiO2 might retard CO production.