Effect of Ceria Crystal Plane on the Physicochemical and Catalytic Properties of Pd/Ceria for CO and Propane Oxidation

Abstract

Ceria nanocrystallites with different morphologies and crystal planes were hydrothermally prepared, and the effects of ceria supports on the physicochemical and catalytic properties of Pd/CeO 2 for the CO and propane oxidation were examined. The results showed that the structure and chemical state of Pd on ceria were affected by ceria crystal planes. The Pd species on CeO 2 -R (rods) and CeO 2 -C (cubes) mainly formed Pd x Ce 1−x O 2−σ solid solution with −Pd 2+ −O 2− −Ce 4+ − linkage. In addition, the PdO x nanoparticles were dominated on the surface of Pd/CeO 2 -O (octahedrons). For the CO oxidation, the Pd/CeO 2 -R catalyst showed the highest catalytic activity among three catalysts, its reaction rate reached 2.07 × 10 −4 mol g Pd −1 s −1 at 50 °C, in which CeO 2 -R mainly exposed the ( 110) and (100) facets with low oxygen vacancy formation energy, strong reducibility, and high surface oxygen mobility. TOF of Pd/CeO 2 -R (3.78 × 10 −2 s −1 ) was much higher than that of Pd/CeO 2 -C (6.40 × 10 −3 s −1 ) and Pd/CeO 2 -O (1.24 × 10 −3 s −1 ) at 50 °C, and its activation energy (E a ) was 40.4 kJ/mol. For propane oxidation, the highest reaction rate (8.08 × 10 −5 mol g Pd −1 s −1 at 300 °C) was obtained over the Pd/CeO 2 -O catalyst, in which CeO 2 -O mainly exposed the (111) facet. There are strong surface Ce−O bonds on the ceria (111) facet, which favors the existence of PdO particles and propane activation. The turnover frequency (TOF) of the Pd/CeO 2 -O catalyst was highest (3.52 × 10 −2 s −1 ) at 300 °C and its E a value was 49.1 kJ/mol. These results demonstrate the inverse facet sensitivity of ceria for the CO and propane oxidation over Pd/ ceria.

Optimizing the Reaction Performance of La2Ce2O7‐Based Catalysts for Oxidative Coupling of Methane (OCM) at Lower Temperature by Lattice Doping with Ca Cations

“…It was reported previously that a well crystallized CeO 2 with an ideal cubic fluorite structure exhibits only one Raman active F 2g mode at ≈ 460 cm –1 , corresponding to the Ce–O bond vibration. However, for poorly crystallized CeO 2 possessing a lot of surface and bulk defects, another peak at ≈ 600 cm –1 corresponding to surface oxygen vacancies can also be observed , . In addition, the doping of La 3+ into CeO 2 lattice can shift the F 2g peak to a lower wavenumber , .…”

“…The Ce 3d spectra of the catalysts are specially depicted and analyzed in Figure . By fixing the FWHM of a single Ce peak in the range of 2.9–3.3 eV,, each spectroscopy can be deconvoluted into 10 groups related to various surface Ce species. Typically, five 3d 5/2 peaks attributed to v 0 (881.7 eV), v (882.9 eV), v′ (885.7 eV), v′′ (889.0 eV) and v′′′ (897.6 eV), and five 3d 3/2 peaks assigned to u 0 (899.1 eV), u (901.2 eV), u′ (903.0 eV), u′′ (907.7 eV), u′′′ (916.8 eV) are clearly observed for the samples .…”

“…By fixing the FWHM of a single Ce peak in the range of 2.9–3.3 eV,, each spectroscopy can be deconvoluted into 10 groups related to various surface Ce species. Typically, five 3d 5/2 peaks attributed to v 0 (881.7 eV), v (882.9 eV), v′ (885.7 eV), v′′ (889.0 eV) and v′′′ (897.6 eV), and five 3d 3/2 peaks assigned to u 0 (899.1 eV), u (901.2 eV), u′ (903.0 eV), u′′ (907.7 eV), u′′′ (916.8 eV) are clearly observed for the samples . According to former reports, the formation of oxygen vacancies is closely related to the oxidation state change of Ce cations in Ce‐related oxide catalysts, which will influence the quantities of vacancy defects or partially reduced oxygen species , .…”

“…Typically, five 3d 5/2 peaks attributed to v 0 (881.7 eV), v (882.9 eV), v′ (885.7 eV), v′′ (889.0 eV) and v′′′ (897.6 eV), and five 3d 3/2 peaks assigned to u 0 (899.1 eV), u (901.2 eV), u′ (903.0 eV), u′′ (907.7 eV), u′′′ (916.8 eV) are clearly observed for the samples . According to former reports, the formation of oxygen vacancies is closely related to the oxidation state change of Ce cations in Ce‐related oxide catalysts, which will influence the quantities of vacancy defects or partially reduced oxygen species , . In other words, the quantity of oxygen vacancies on CeO 2 surface is intimately related to the surface Ce 3+ concentration.…”

Continuous hydrothermal flow synthesis of Gd‐doped CeO2 (GDC) nanoparticles for inkjet printing of SOFC electrolytes

“…3,4 CeO 2 also can be employed as a catalyst or catalyst support for noble metals or oxides applied for catalytic gas oxidation reactions. [5][6][7] Among the possible synthesis routes, the solvothermal/ hydrothermal synthesis of CeO 2 -based oxides is often used when aiming for nanosized materials. 8 Usually taking place in an aqueous system, hydrothermal synthesis of CeO 2 -based oxide nanomaterials proceeds by hydration of metal salts followed by dehydration, crystallization, and growth of oxides from a supersaturated solution at an increased temperature and pressure.…”