Clark Adam H, Marchbank Huw R, Thompsett David, Fisher Janet M, Longo Alessandro, Beyer Kevin A, Hyde Timothy I, Sankar Gopinathan
Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK.
Johnson Matthey Technology Centre, Blount's Court, Sonning Common, Reading RG4 9NH, UK.
Phys Chem Chem Phys. 2022 Jan 26;24(4):2387-2395. doi: 10.1039/d1cp04654c.
The effect of Pd loading on the redox characteristics of a ceria support was examined using Pd K-edge XAS, Ce L-edge XAS and X-ray diffraction techniques. Analysis of the data obtained from these techniques indicates that the onset temperature for the partial reduction of Ce(IV) to Ce(III), by exposure to H, varies inversely with the loading of Pd. Whilst the onset and completion temperatures of the reduction of Ce(IV) to Ce(III) are different, both samples yield the same maximal fraction of Ce(III) formation independent of Pd loading. Furthermore, the partial reduction of Ce is found to be concurrent with the reduction of PdO and demonstrated that the presence of metallic Pd is necessary for the reduction of the CeO support. Upon passivation by room temperature oxidation, a full oxidation of the reduced ceria support was observed. However, only a mild surface oxidation of Pd was identified. The mild passivation of the Pd is found to lead to a highly reactive sample upon a second reduction by H. The onset of the reduction of Pd and Ce has been demonstrated to be independent of the Pd loading after a mild passivation with both samples exhibiting near room temperature reduction in the presence of H.
使用钯K边X射线吸收光谱（XAS）、铈L边XAS和X射线衍射技术研究了钯负载量对二氧化铈载体氧化还原特性的影响。对这些技术获得的数据进行分析表明，通过暴露于氢气将Ce(IV)部分还原为Ce(III)的起始温度与钯的负载量成反比。虽然Ce(IV)还原为Ce(III)的起始温度和完成温度不同，但两个样品生成的Ce(III)最大比例相同，与钯负载量无关。此外，发现Ce的部分还原与PdO的还原同时发生，并且表明金属钯的存在对于CeO载体的还原是必要的。通过室温氧化进行钝化后，观察到还原的二氧化铈载体完全氧化。然而，仅鉴定出钯的轻度表面氧化。发现钯的轻度钝化会导致样品在第二次氢气还原时具有高反应活性。在轻度钝化后，钯和铈还原的起始温度已被证明与钯负载量无关，两个样品在氢气存在下均表现出接近室温的还原。
