Synergetic Effects of PdO Species on CO Oxidation over PdO–CeO₂ Catalysts

Abstract

The PdO/Ce1–x Pd x O2−δ catalyst prepared by a solution-combustion method contained free surface PdO species and PdO species in Ce1–x Pd x O2−δ solid solution, whereas the PdO/CeO2 catalyst prepared by an impregnation method contained only free surface PdO species. The free surface PdO species could be removed by nitric acid. Contributions of the PdO species to catalytic CO oxidation were quantitatively evaluated. The free surface PdO species in the PdO/Ce1–x Pd x O2−δ catalyst had the highest activity (969.3 μmolCO gPd –1 s–1), those in the PdO/CeO2 catalyst had medium activity (109.0 μmolCO gPd –1 s–1), and the PdO species in the Ce1–x Pd x O2−δ solid solution had the lowest activity (13.2 μmolCO gPd –1 s–1). Synergetic effects of PdO species were responsible for the enhanced reactivity of the PdO/Ce1–x Pd x O2−δ catalyst, as the free surface PdO species provided CO chemisorption sites and the Ce1–x Pd x O2−δ solid solution generated more oxygen vacancies for oxygen activation.

Oxygen vacancy promoted CO oxidation over Pt/CeO 2 catalysts: A reaction at Pt–CeO 2 interface

“…Most of the Pt 2+ species are embedded in CeO 2 matrix due to the formation of Pt-Ce-O solid solution, which makes the CO molecules not accessible to these species. Similar findings were also reported in PdO/CeO 2 [39] and CuO/CeO 2 [23] catalysts. For example, Meng et al [39] reported CO chemisorption on a PdO/CeO 2 catalyst; however, there is no CO chemisorption on the catalyst when the surface Pd species were removed by a nitric acid treatment even though oxidized Pd species were detected in the catalyst (in form of Pd-Ce-O solid solution).…”

“…Similar findings were also reported in PdO/CeO 2 [39] and CuO/CeO 2 [23] catalysts. For example, Meng et al [39] reported CO chemisorption on a PdO/CeO 2 catalyst; however, there is no CO chemisorption on the catalyst when the surface Pd species were removed by a nitric acid treatment even though oxidized Pd species were detected in the catalyst (in form of Pd-Ce-O solid solution). Thus, in the current case we believe that the CO chemisorption on the Pt/CeO 2 catalysts mainly takes place on the surface metallic Pt species (as the catalysts were pre-reduced in H 2 ) but the oxidized Pt species are not accessible for the CO molecules.…”

“…It was found that the activity was proportional to the concentration of oxygen vacancy in the sample, suggesting a pivotal role of oxygen vacancy in the CO oxidation. Similar role of the presence of oxygen vacancies in CO oxidation was also observed on PdO-CeO 2 catalysts [39], which was also evidenced by theoretical calculation [45]. Another noteworthy point is the contributions of Pt 0 and Pt 2+ species in the reactivity in CO oxidation.…”

Structural determination and electronic properties of the 4dperovskite SrPdO3

“…In particular, noble metal incorporated perovskites represent a valuable alternative as catalysts since they have a high thermal stability and their elevated compositional flexibility along with the presence of chemically active structural defects and localized electronic states offer tremendous tailoring possibilities for designing more efficient catalytic processes. 8,20,21 Palladium oxides is one of the most useful catalyst in oxidation reaction 22,23 and the incorporation of Pd in perovskite structure turned out to efficiently suppress the inconvenient clustering of Pd particles, thereby improving the catalytic activity.…”

Solid-State Method Toward PdO-CeO2 Coated Monolith Catalysts for Oxygen Elimination Under Excess Methane

“…Previous studies on Pd-CeO 2 catalysts were usually calcined at temperatures below 600°C and CO oxidation performance was used as conventional indicator for evaluating the degree of metal-support interaction [21]. When supported Pd-Ce oxides are thermally treated at higher temperatures, the activity is generally considered to decrease to some content due to aggregation of Pd or sintering of supports [22].…”