Simulation three-way catalyst ageing: Analysis of two conventional catalyst
TL;DR: In this article, two commercial automobile three-way catalysts (RENAULT) of different configuration: (I) Pt, Rh active phase supported on ceria-promoted alumina washcoat, and (II) Pd, RH active phase supporting on zirconia-ceria-promosed alumina soapboard on cordierite supports, have been compared fresh and aged in a conventional automobile for 100,000 km in order to design and adjust a catalyst ageing method suitable to imitate most relevant conditions of real tests.
Abstract: Two commercial automobile three-way catalysts (RENAULT) of different configuration: (I) Pt, Rh active phase supported on ceria-promoted alumina washcoat, and (II) Pd, Rh active phase supported on zirconia-ceria-promoted alumina washcoat on cordierite supports, have been compared fresh and aged in a conventional automobile for 100,000 km in order to design and to adjust a catalyst ageing method suitable to imitate most relevant conditions of real tests. The characterization techniques were N2 adsorption–desorption isotherms, powder X-Ray diffraction, elemental chemical analysis and activity tests. Activity tests were: (1) CO, NO and CH4 conversion versus temperature (from 120 to 500 °C), and (2) CO, NO and CH4 conversion versus the ratio between the concentrations of the oxidant and reducing species (λ) at 500 °C (normal running temperature). Gas composition was close to conventional engine exhaust composition with and without water vapour. A strong deactivation has been observed as a consequence of thermal processes and loss of catalyst washcoat mainly for catalyst (II). Poison concentration along the catalyst has also been shown, however, its influence on catalyst deactivation was not as important as thermal processes were.
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TL;DR: In this article, a series of manganese−cerium oxide composites with Mn concentrations in the range of 1−20 mol % in ceria was prepared by the solution combustion technique using urea as fuel.
Abstract: A series of manganese−cerium oxide composites with Mn concentrations in the range of 1−20 mol % in ceria was prepared by the solution combustion technique using urea as fuel. The nature, type, and oxidation state of Mn species in ceria were investigated by X-ray diffraction (XRD), diffuse reflectance UV−visible spectroscopy, electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy, and temperature-programmed reduction techniques. The study reveals that the method of preparation significantly influences the type of manganese species in ceria. Wet-impregnation, coprecipitation, and solid-state synthesis techniques lead to clustered MnOx-like species in the ceria matrix, while the present method of preparation (solution combustion route) yields a highly dispersed form of Mn species. In the reported series of samples, Mn is present mainly in +2 and +3 oxidation states and there is no evidence for the presence of Mn4+ species. Powder X-ray diffraction studies at variable temperatures (298−1323 K...
186 citations
TL;DR: In this article, the behavior of Pd three-way catalysts promoted with Ce-Zr mixed oxides and supported on alumina subjected to thermal degradation treatments has been examined during light-off tests under stoichiometric CO+NO+O 2.
116 citations
01 Sep 1978
TL;DR: In this article, the poisoning process at exhaust stoichiometry appears to be very similar to poisoning process under net oxidizing conditions; that is, only a sharply defined outer shell of the pellets is poisoned, this shell progressing inward as time elapses.
Abstract: Experiments designed to answer certain questions about the mechanism of operation and of deactivation of catalysts near stoichiometric conditions were carried out. This involved special catalysts preparations tested in laboratory equipment and in vehicles. We concluded that the poisoning process at exhaust stoichiometry appears to be very similar to the poisoning process under net oxidizing conditions; that is, only a sharply defined outer shell of the pellets is poisoned, this shell progressing inward as time elapses. Based on these experiments, the following catalyst design concept was developed: To utilize the different properties of Pt, Pd and Rh, all three will have to be employed in a special design corresponding to their ratio in ores. To avoid interferences, they should not be coimpregnated over the same support surface; one way to avoid coimpregnation is to impregnate them in separate layers in the catalyst pellets. Due to its relative poison insensitivity Pt should be the outer layer, while Pd and Rh should be protected from the poison front. Consequenty, the Pt impregnation depth (from the outer surface) is given by the depth to which the poisons penetrate. Due to the importance of Rh in catalyzing the NO reduction reaction at the (diffusionmore » controlled) rich end of the A/F scale, Rh should be impregnated as close to the surface of the pellet as possible, while still being protected from poisoning. Consequently, Rh should be impregnated right below the Pt layer and Pd underneath the Rh layer. Due to the transient nature of the feedstream's A/F, it appears to be beneficial to include an agent in catalyst formulations which, by storing and slowly releasing some of the components from the surface, tends to smooth out the effects of A/F oscillations. The results are encouraging; real-time engine dynamometer and vehicle aging tests are required, however, to prove their durability in actual automobile service.« less
100 citations
TL;DR: In this article, the catalytically important Mn/CeO2−TiO2 (MCT) solid solutions were synthesized by solution combustion technique using glycine, urea, or PEG as fuel.
Abstract: The catalytically important Mn/CeO2−TiO2 (MCT) solid solutions were synthesized by solution combustion technique using glycine, urea, or PEG as fuel. These samples along with those prepared by coprecipitation and wet impregnation methods were characterized for its structural, textural and redox properties using various physical and spectroscopic techniques, viz., powder X-ray diffraction, high-resolution transmission electron microscopy, temperature-programmed reduction, diffuse reflectance UV−visible, electron paramagnetic resonance, and X-ray photoelectron spectroscopy. The samples prepared by the solution combustion method showed high thermal stability, even at temperatures of 1323 K, whereas the samples synthesized by conventional routes lost its structural integrity at higher temperatures due to fast sintering. The combustion and coprecipitation methods stabilize Mn species both in +2 and +3 oxidation states, while in the MCT sample prepared by wet impregnation, Mn ions are present in +3 state exclus...
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TL;DR: The role of La doping with different content in the structure of Ce0.2Zr0.8O2 solid solution and the effect of modification on the catalytic activity of supported Pd-only three-way catalysts (TWCs) are clarified in this article.
Abstract: The role of La doping with different content in the structure of Ce0.2Zr0.8O2 solid solution (CZ) and the effect of modification on the catalytic activity of supported Pd-only three-way catalysts (TWCs) are clarified. The characterization results reveal that the introduction of La into the lattice of CZ is facile. Zr is replaced by the doped La firstly at low doping content and then Ce is substituted further with increasing La content. The substitution occurs in the bulk preferentially, and then in the surface. The addition of La results in preferable thermal stability, higher BET surface area and enhanced oxygen storage capacity (OSC) compared with CZ, due to the structure modification. La doped fresh samples are beneficial to the conversion of NO and the corresponding aged samples exhibit higher activity for the conversion of all the target pollutants.
73 citations
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TL;DR: In this paper, the use of CeO 2 -based materials in the automotive three-way catalysts (TWCs) is considered, and the multiple roles of COO 2 as a TWC promoter and in particular the oxygen storage/release capacity (OSC) are critically discussed.
1,632 citations
132 citations
TL;DR: Pd-loaded Ce06Zr04O2 solid solutions supported on Al2O3 are investigated as catalysts for the reduction of NO by CO in this article, where the authors focused on the role of the CZr4O2 and of the Pd dispersion on the catalytic activity.
Abstract: Pd-loaded Ce06Zr04O2 solid solutions supported on Al2O3 are investigated as catalysts for the reduction of NO by CO The attention is focused on the role of the Ce06Zr04O2 and of the Pd dispersion on the catalytic activity The system shows a very high activity below 500 K, which is almost independent on the Pd dispersion The high activity is attributed to a promoting effect of the Ce06Zr04O2 on the NO conversion Investigation of the influence of high temperature treatments disclosed a thermal stabilisation of both Ce06Zr04O2 and Al2O3 in the Ce06Zr04O2/Al2O3 system
116 citations
TL;DR: In this paper, the authors investigated several features of the operation of noble metal catalysts in automobile exhaust near the stoichiometric air:fuel ratio (A F ), including the extent of intrapellet diffusion limitations as a function of feedstream stoichiometry, the mechanism of poisoning, and the effects of impregnation profiles on activity and poison resistance.
100 citations