Pd-Supported Interaction-Defined Selective Redox Activities in Pd−Ce_0.7Zr_0.3O₂−Al₂O₃ Model Three-Way Catalysts

Abstract

Effects of Pd-supported interactions toward redox behaviors concerning three-way catalytic reactions and oxygen-buffering effects are investigated through stepwise changing Pd-loading locations over ceria−zirconia and alumina. Through light-off tests and kinetics, texture, and surface studies, discrepant but redistributable Pd−A2O3 and Pd−Ce0.7Zr0.3O x interfaces are defined and analyzed. Pd species are inclined to promote the transformation of Ce4+ to Ce3+ and maintain themselves as fine particles on ceria−zirconia surfaces. Oxygen spillover promoted by Pd n+/Pd0−Ce4+/Ce3+ redox couples benefits the oxygen-buffering effect, but is limited by the increase of reaction temperatures and ceria−zirconia reducibility. This strong oxidative interaction overcomes the possibility of ceria-related anionic vacancies in facilitating NO dissociation and, thus, improves CO conversion only. Stochiometric light-off tests show higher activities for NO reduction and C3H8 oxidation on a Pd−Al2O3 interface, where the different morphologies and redox states of Pd-supported interfaces should be the main contributing factors for efficient molecular bond dissociation.

Pd supported on SnO2–MnO –CeO2 catalysts for low temperature CO oxidation

“…No CO absorption was observed on the SMC solid solution support, while two absorption bands were observed for the Pd-SMC catalyst. The band at 1979 cm −1 can be attributed to CO adsorbed on bridge sites of metallic Pd, while the band at 2092 cm −1 is due to CO adsorption on atop sites of metallic Pd [39,40]. There are no absorption peaks observed in the ranges of 2120-2110 cm −1 and 2180-2160 cm −1 , corresponding to Pd + and Pd 2+ species [41], respectively.…”

Ambient Temperature NO Adsorber Derived from Pyrolysis of Co-MOF(ZIF-67)

“…Nitrogen Oxides (NOx) emitted from automobiles has long been recognized as a major pollutant to the environment and to human health. Over the past decades, three-way catalysis, 1,2 NOx storage and reduction, 3,4 and selective catalytic reduction 5−8 processes have been developed and commercialized to eliminate NOx generated by vehicles. Even though these processes are highly efficient, and certainly responsible for the air quality improvement we have experienced in recent years, none of them can eliminate 100% tailpipe NOx, especially during the so-called “cold-start”.…”

DRIFTS study of the role of alkaline earths in promoting the catalytic activity of HC and NOx conversion over Pd-only three-way catalysts

“…1 In recent years, Pd supported on various CeO 2 -ZrO 2 mixed oxides has been studied for exhaust catalysis with great interest because of the associated low cost and high activity. [2][3][4] However, the evolution towards more strict standards in gasoline exhaust emissions requires a decrease of cold-start emissions (especially HC and NO x ). Therefore, considerable efforts have focused on improving the NO x and HC elimination activities of Pd-only three-way catalysts by structural modification with electropositive promoters, such as rare earths, transition earths and alkaline earths.…”