Elucidating the role of surface Ce sites in the enhanced low temperature reduction of Pd-loaded CeO2–ZrO2 using infrared spectroscopy

Abstract

The reduction behavior of La₂O₃–CeO₂–ZrO₂ mixed oxide (LCZ) and Pd-loaded LCZ (Pd/LCZ) was analyzed in detail using infrared spectroscopy (IR). During temperature-programmed reduction with CO as the reductant gas (CO-TPR), an infrared absorption peak caused by the electronic transition of Ce³⁺ (²F_5/2 → ²F_7/2) was observed. This observation enabled an evaluation of the reduction rate of Ce in LCZ. Furthermore, the state of surface Ce sites at each reduction degree was also analyzed by IR using methanol as a probe. The results indicated that the presence of Pd significantly promotes the reduction of surface Ce sites, followed by the reduction of bulk Ce. The analytical method proposed has the potential to further accelerate the development of oxygen storage materials used in three-way catalysts.