Phase-dependent enhancement for CO2 photocatalytic reduction over CeO2/TiO2 catalysts

Abstract

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.