Superior TWC activity of Rh supported on pyrochlore-phase ceria zirconia

Superior Pd–Rh Three-Way Catalyst: Modulating the Surface Composition by Introducing Ceria-Zirconia with Partial κ-Ce2Zr2O8 Structure as Support

“…Generally, the cubic CeO 2 structure only has one Raman-allowed mode while the tetragonal phase has six. For CZ, in addition to the dominant band at 468 cm –1 , which is ascribed to the triply degenerate F 2g mode of the cubic fluorite structure of CeO 2 , it also shows less obvious shoulders at 144 cm –1 , 272 cm –1 , 308 cm –1 , implying cubic and tetragonal phase coexist in CZ. ,, Besides, κCZ exhibits five characteristic bands at 275, 293, 441, 480, and 600 cm –1 , showing the formation of κ-Ce 2 Zr 2 O 8 structure in agreement with Ding et al and Montini et al Meanwhile, the band around 600 cm –1 , the defect-induced mode, is related to oxygen vacancies. The value of A 600 / A 468 , which implies the oxygen defect concentration, is larger in κCZ than in CZ, indicating that more concentration of oxygen vacancies is obtained by κCZ.…”

“…Therefore, it is not hard to state that κCZ possesses better reducibility and lower average oxygen vacancy energy compared with CZ. However, the barrier to implementation of κ-Ce 2 Zr 2 O 8 with high purity is its intrinsic low surface area, which limits the oxygen release rate and results in a less functional catalyst when used as support for PGMs . According to the results of BET surface area, κCZ possesses a large specific surface area (52.5 m 2 /g), which is similar to that of CZ (51.4 m 2 /g).…”

“…In parallel, for Rh, the SAE paper stated that κ-Ce 2 Zr 2 O 8 can effectively weaken the undesirable Rh–CZ interaction, showing that the Rh-based catalyst with κ-Ce 2 Zr 2 O 8 as support exhibited increased NO x conversion despite the 33% decrease of PGMs weight. Similarly, Wu et al claimed κ-Ce 2 Zr 2 O 8 was a desirable support for Rh because it weakened the MSI originating from lowering the Rh–O–Ce interface while increasing the overall OSC owing to its improved bulk oxygen mobility. However, a significant deactivation was observed in Rh/Pd supported on the κ-Ce 2 Zr 2 O 8 structure with high purity, presumably owing to its low surface area leading to sintered Rh/Pd after aging.…”

Effect of oxygen storage materials on the performance of Pt-based three-way catalysts

“…Compared to Al 2 O 3 -based commercial TWC supports [31][32][33][34][35] and other promising metal oxide supports, 36,37 oxygen storage materials (OSMs) such as CeO 2 and CeO 2 -ZrO 2 solidsolutions are effective for control of air-fuel ratios (AFRs) that deviate from the stoichiometric conditions (λ = 1) in realworld applications; that is because OSMs possess excellent oxygen storage capacity (OSC) due to the rapid redox reaction of Ce, between its 4+ and 3+ oxidation states. [38][39][40][41][42][43][44][45][46][47] Introducing the Zr 4+ cation into the lattice of CeO 2 increases the concentration of structural defects, improves the oxygen mobility, and enhances the Ce 3+ /Ce ratio on the surface of PGM-based catalysts, producing more oxygen vacancies and Ce in the Ce 3+ state. [48][49][50][51] Note that such structural defects should only be local perturbation and the overall structure should be homogeneous on average as the dynamic oxygen mobility in Pt/CeO 2 -ZrO 2 catalysts was proportional to the structural homogeneity arising from the introduction of Zr into the CeO 2 framework.…”

An effective selective catalytic reduction catalyst contains oxygen bridge for NO x reduction based on low concentration of C 3 H 6 at medium‐low temperatures

“…NO x is generally emitted from the combustion of fossil fuels from stationary and mobile sources, and strict regulations have been formulated all over the world to reduce NO x emissions 2 . For NO x from mobile sources, three‐way catalysts show great performance on vehicles 3 . For thermal power plants and refineries, low nitrogen combustion technology, fuel reburning, and flue gas recirculation technologies have been taken to control NO x emission before combustion, and flue gas purification technology has been used as postcombustion technology 4 .…”