Promoting the Methane Oxidation on Pd/CeO₂ Catalyst by Increasing the Surface Oxygen Mobility via Defect Engineering

Abstract

Methane is a useful chemical resource, but removing it, a powerful greenhouse gas, is important to prevent global warming. In this study, the methane oxidation activity of conventional Pd/CeO2 catalyst was improved by enhancing the oxygen mobility of ceria surface via the simple defect engineering. Raman spectroscopy demonstrates that the defect concentration of ceria surface is reduced after high temperature treatments. Cryogenic hydrogen‐temperature‐programmed‐reduction curves indicate that the surface oxygen of ceria in Pd/CeO2 catalysts with the reduced defect concentration became mobile, resulting in the facile reduction at the lower temperature. X‐ray diffraction, X‐ray photoelectron and X‐ray adsorption spectroscopies show that the improvement in the surface oxygen mobility does not originate from the change in PdOx particle size nor its oxidation state. As a result, the temperature of 50 % conversion of methane shifted by 25 °C to the lower temperature on Pd/CeO2 catalyst with the reduced defect concentration. This work highlights that the catalytic activity can be enhanced by promoting the active participation of the surface oxygen of support.

Single Ru(II) Ions on Ceria as a Highly Active Catalyst for Abatement of NO

“…If Ru–NO complexes indeed form, then, Ru ceria should be able not to just oxidize NO but also store NO at lower temperatures: this storage is critical during vehicle cold-start and idle operation when the temperatures of exhaust are lower (∼100–120 °C) and no known catalyst can provide NO x removal at this temperature. More specifically, Pd/zeolite formulations can store NO x at low temperatures (∼100 °C) and release them continuously at >180 °C. − Pd is expensive, and loadings of ∼ at least 1–2 wt % are required to achieve optimal NO adsorption.…”

Spatiotemporal insights into forced dynamic reactor operation for fast light-off of Pd-based methane oxidation catalysts

“…According to recent findings, these redox dynamics are hampered by hydroxylation 18 and several studies in the field of lean methane oxidation underscored the importance of an oxygen exchange between the noble metal particles and the metal oxide support material. 23,54,55 Therefore, using CeO 2 as a support material with its high oxygen mobility has been suggested for improving water tolerance. 16,54,56 Despite these beneficial properties, ceriabased Pd catalysts still suffer from the presence of steam if operated under static lean conditions.…”

Catalytic Combustion of Methane: From Mechanism and Materials Properties to Catalytic Performance

“…Therefore, many strategies were applied to modify the properties of CeO 2 for Pd/CeO 2 catalysts. Lee et al 95 discovered that lattice defects in the surface of CeO 2 decreased with the increment of calcination temperature under an oxidative atmosphere, which promoted the oxygen mobility of CeO 2 and thus enhanced the performance of Pd/CeO 2 . The sequence of catalytic activity examined by Chen et al 96 among Pd/CeO 2 with different CeO 2 morphologies was Pd/CeO 2 nano-octahedrons (CeO 2oct) > Pd/CeO 2 nanocubes (CeO 2 -cube) ≫ Pd/CeO 2 nanorods (CeO 2 -rod), which was ascribed to the difference in Pd 0 /Pd 4+ content caused by varied exposed facets of CeO 2 and the influence of lattice defects (see Figure 7).…”