High temperature reduction dramatically promotes Pd/TiO2 catalyst for ambient formaldehyde oxidation

- High temperature reduction dramatically increased the Pd/TiO2 activity for HCHO oxidation.
- High temperature reduction decreased the average particle sizes of Pd particles.
- High temperature reduction promoted the activation of oxygen and H2O.
- HCHO oxidation followed two different pathways over Pd/TiO2-300R and Pd/TiO2-450R catalysts.

High temperature reduction generally induces the sintering of supported noble metals, therefore resulting in a negative effect on their performance. Here, we show that high temperature reduction was able to dramatically increase the activity of Pd/TiO2 for ambient HCHO oxidation. We prepared a Pd/TiO2 catalyst and pre-reduced it with H2 at low temperature (300 °C) and high temperature (450 °C), respectively, and then tested the activity for HCHO oxidation at ambient temperature. The Pd/TiO2-450R catalyst showed a much better performance than Pd/TiO2-300R at room temperature. 100% HCHO conversion could be obtained on the Pd/TiO2-450R catalyst at a GHSV of 95000 h−1 and 140 ppm inlet HCHO. The catalysts were then characterized by using Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and other methods. The results indicate that high temperature reduction could induce the strong metal-support interaction (SMSI), decreasing the surface Pd particle size by partially encapsulating and trapping Pd clusters with TiO2, and also could produce more oxygen vacancies, beneficial to the activation of O2 and formation of surface OH groups, opening a more effective pathway for ambient HCHO oxidation. Therefore, the Pd/TiO2-450R catalyst demonstrated high activity for ambient HCHO oxidation.

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