Deactivation Mechanism of Pd/CeO₂–ZrO₂Three-Way Catalysts Analyzed by Chassis-Dynamometer Tests andin SituDiffuse Reflectance Spectroscopy

Abstract

The thermal deactivation of engine-aged Pd/CeO2–ZrO2 three-way catalysts was studied by chassis-dynamometer driving test cycles with cold start and in situ diffuse reflectance spectroscopy (DRS). The extent of the catalyst deactivation after engine-aging at 800–1000 °C was correlated with the microstructural evolution, which was analyzed by X-ray diffraction, X-ray absorption spectroscopy, electron microscopy, and a chemisorption technique. This suggests that deactivation is caused by degradation of the catalytically active sites in the three-phase boundary (TPB) region, where Pd, CeO2–ZrO2, and the gas phase meet. The time-resolved in situ DRS revealed that the reoxidation of Pd metal under fluctuating air-to-fuel ratios was retarded relative to the reduction of Pd oxide. The retardation is attributable to the oxygen storage in CeO2–ZrO2. In the fresh catalyst with a high dispersion, most Pd was close to the TPB. Conversely, after engine-aging at elevated temperatures, the retardation effect was less pronounced with respect to Pd particle growth. Grown into large Pd particles, the Pd at sufficient distances from the TPB was no longer affected by the oxygen storage. Consequently, from the ratios of the initial rate constants of the Pd oxidation and reduction under fluctuating air-to-fuel ratio conditions, we can understand the quality and/or quantity of the TPB site in engine-aged catalysts. This measure provides a useful index of the extent of catalyst deactivation.

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

“…As Machida et al. pointed out, the reduction and re‐ oxidation of Pd become less retarded by ceria support as the size of Pd cluster increases [13] . The reduction peak of PdO x shifted to the lower temperature as the Pd loading increased (Figure 2b).…”

Characterization of the Evolution of Noble Metal Particles in a Commercial Three-Way Catalyst: Correlation between Real and Simulated Ageing

“…The chosen catalyst technology, already used in our previous work [29], is a commercial formulation, based on double metal Pd/Rh technology (55:5), with a total PGM loading of 60 g/ft 3 (1 wt.%), supported on a porous substrate mainly composed by Ce, Zr and Al oxides, with dopants (Ba, La). The component, a cylindrical ceramic monolith of 0.55 L (4.2′′ × 2.5′′) characterized by a high density of channels (900 cpsi) with hexagonal shape, was core drilled to obtain two cylindrical samples of 1.5′′ of diameter and 2.5′′ length, one for the morphological characterization, one for the functional testing.…”

“…This is particularly true in gasolinefueled vehicles, where the main system adopted to reduce engine emissions is represented by the three-way catalyst (TWC) [1,2]. This catalytic system is able to perform simultaneous oxidation of CO and unburned hydrocarbons (HC) and reduction of nitrogen oxides (NOx), thanks to a well-controlled air-to-fuel ratio that keeps the gaseous stream around stoichiometry [3]. These conditions promote a series of phenomena called thermal ageing which are the primary sources of catalyst deactivation [4][5][6].…”

Activating Lattice Oxygen at the Twisted Surface in a Mesoporous CeO2Single Crystal for Efficient and Durable Catalytic CO Oxidation

“…Redox activity of isolated Pt 1 ions is more flexible than Ce ions in lattice, which leads to the effective activation of lattice oxygen linked to Pt in local structures. Three‐way catalysis is one of the effective approaches to reduce automotive exhaust emissions, which would vigorously maintain the sustainable development of engine vehicles [11–15] . Catalytic oxidation of the harmful gases like typical CO with air at reduced temperature would be preferred to minimize the automotive exhaust emissions [16–19] .…”

“…Three-way catalysis is one of the effective approaches to reduce automotive exhaust emissions, which would vigorously maintain the sustainable development of engine vehicles. [11][12][13][14][15] Catalytic oxidation of the harmful gases like typical CO with air at reduced temperature would be preferred to minimize the automotive exhaust emissions. [16][17][18][19] CeO 2 with supported Pt catalysts are widely applied in CO oxidation normally at temperatures above about 150 8C that is ascribed to the limited activation of lattice oxygen and the strong chemisorption of CO on Pt.…”