No decomposition over partially reduced metallized CeO2 containing catalysts
TL;DR: M/CeO2-ZrO2 (M=Rh, Pt) solid solutions are investigated as catalysts for the reduction of NO by CO in this article, and it is shown that incorporation of CeO2 into a ZrO 2 framework strongly promotes the reduced support of the metallized support.
Abstract: M/CeO2-ZrO2 (M=Rh, Pt) solid solutions are investigated as catalysts for the reduction of NO by CO. It is shown that incorporation of CeO2 into a ZrO2 framework strongly promotes the reduction of the metallized support. The reduced support efficiently decomposes NO suggesting a direct participation of the support in the NO conversion.
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TL;DR: In this article, computer simulation techniques have been used to model cubic CeO2−ZrO2 solid solutions in the whole composition range and the energetics of the Ce4+/Ce3+ bulk reduction reaction as well as the activation energy for oxygen migration in the lattice are investigated.
Abstract: Computer simulation techniques have been used to model cubic CeO2−ZrO2 solid solutions in the whole composition range. Aspects related with the oxygen storage capacity of these materials are emphasized. The energetics of the Ce4+/Ce3+ bulk reduction reaction as well as the activation energy for oxygen migration in the lattice are investigated and compared with the corresponding quantities in pure CeO2. It is found that even small additions of ZrO2 decrease the bulk reduction energy of Ce4+ to values comparable to those reported for surface reduction in pure CeO2. Activation energy calculations indicate an almost monotonic increase of oxygen mobility with increasing zirconia content.
221 citations
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TL;DR: In this paper, a series of Fe2O3-CeO2 composite catalysts were synthesized by coprecipitation and characterized by X-ray diffraction (XRD), Raman spectroscopy, and X-Ray photoelectron spectrography (XPS).
Abstract: A series of Fe2O3–CeO2 composite catalysts were synthesized by coprecipitation and characterized by X-ray diffraction (XRD), BET surface area measurement, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). Their catalytic activities in CO oxidation were also tested. The Fe2O3–CeO2 composites with an Fe molar percentage below 0.3 form solid solutions with the CeO2 cubic fluorite structure, in which the doped Fe3+ initially substitutes Ce4+ in fluorite cubic CeO2, but then mostly locate in the interstitial sites after a critical concentration of doped Fe3+. With an Fe molar percentage between 0.3 and 0.95, the Fe2O3–CeO2 composites are mixed oxides of the cubic fluorite CeO2 solid solution and the hematite Fe2O3. XPS results indicate that CeO2 is enriched in the surface region of Fe2O3–CeO2 composites. The Fe2O3–CeO2 composites have much higher catalytic activities in CO oxidation than the individual pure CeO2 and Fe2O3, and the Fe0.1Ce0.9 composite shows the best catalytic performance. The structure-activity relation of the Fe2O3–CeO2 composites in CO oxidation is discussed in terms of the formation of solid solution and surface oxygen vacancies. Our results demonstrate a proportional relation between the catalytic activity of cubic CeO2-like solid solutions and their density of oxygen vacancies, which directly proves the formation of oxygen vacancies as the key step in CO oxidation over oxide catalysts.
171 citations
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TL;DR: In this paper, the role of the oxygen storage and release capacity (OSC) in promoting the activity of noble metals in the three-way catalysts (TWCs) is critically discussed.
Abstract: The role of the so-called oxygen storage and release capacity (OSC) in promoting the activity of noble metals in the three-way catalysts (TWCs) is critically discussed. It is shown that the promoting effects of CeO2 in the TWCs cannot be attributed to a simple redox type of effect according to the reaction CeO2 ↔ CeO2 − x + x/2O2, since multiple and sometimes intriguing effects of CeO2 promoter have been observed, particularly in the latest generation of TWCs containing modified CeO2–ZrO2 mixed oxides.
166 citations
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TL;DR: In this article, the reduction behavior of a high surface area CeO2-ZrO2 solid solution is compared with that of a low surface area C2C solution.
Abstract: The reduction behaviour of a high surface area CeO2-ZrO2 solid solution is compared with that of a high surface area CeO2. It is shown that, upon sintering induced by repetitive reduction/oxidation processes, the temperature of reduction of the solid solution decreases from 900 to 700 K. In contrast, the reduction at low temperatures of the CeO2 sample is strongly retarded after such treatments. The role of ZrO2 in promoting the reduction at low temperatures is discussed.
162 citations
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TL;DR: A series of ceria-incorporated zirconia (Ce1−xZrxO2,x = 0 to 1) solid solutions were prepared by employing the solution combustion synthesis route as discussed by the authors.
Abstract: A series of ceria-incorporated zirconia (Ce1−xZrxO2,x = 0 to 1) solid solutions were prepared by employing the solution combustion synthesis route. The products were characterized by XRD and UV-Vis-NIR diffuse reflectance spectroscopy. The materials are crystalline in nature and the lattice parameters of the solid solution series follow Vegard’s law. Diffuse reflectance spectra of the solid solutions in the UV region show two intense bands at 250 and 297 nm which are assigned respectively to Ce3+ ← O2−and Ce4+ ← O2− charge transfer transitions. The two vibrational bands in 6960 cm−1 and 5168 cm−1 in the NIR region indicate the presence of surface hydroxyl groups on these materials.
149 citations
References
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01 Jan 1982
TL;DR: In early spring 1996, this article published a complete handbook on science and technology of catalysis, which is available as a set for a reduced price for all scientists working in the fields of kinetics and homogenous or heterogenous catalysis.
Abstract: In early spring 1996 our handbook on science and technology of catalysis will be completed In order to give all scientists working in the fields of kinetics and homogenous or heterogenous catalysis the possibility to have this detailed treatise of the topic on his or her shelf we decided to offer the whole handbook as a set for a reduced price
1,689 citations
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TL;DR: In this article, the authors measured the oxygen removal at various temperatures using TPR traces of unsupported or alumina-supported ceria and showed that the reduction of surface capping oxygen and bulk oxygen anions is associated with reduction of the shared oxygen anion at the interface.
Abstract: Oxygen storage capacities of CeO 2 , CeO 2 Al 2 O 3 , and PM/CeO 2 /Al 2 O 3 , measured by a pulse injection method, are affected by pretreatment temperature, pulsing temperature, partial pressure of CO, presence of precious metals (PM), and the concentration of CeO 2 on alumina They are lowered by higher pretreatment temperature but increase with the pulsing temperature in the range of application At a pulsing temperature ≤500 °C, the capacities are not affected by oxygen pressure but increase with partial pressure of CO The presence of PM lowers the reduction temperature and increases the oxygen storage capacity of CeO 2 TPR was used to measure the oxygen removal at various temperatures At 900 °C, the maximum amount of oxygen removed from unsupported or alumina-supported ceria is about 25% The TPR traces of the unsupported ceria show two peaks at 500 and 750 °C which are associated with the reduction of surface capping oxygen and bulk oxygen anions, respectively For alumina-supported ceria, the TPR traces show a third peak at 850 °C which is associated with the reduction of the shared oxygen anions at the interface The presence of PM lowers only the reduction temperature of the capping oxygen anions but not of the other two oxygen species Both oxygen chemisorption and TPR were used to measure the oxygen anion restoration at various temperatures following the reduction at 500 and 900 °C, respectively Chemisorption data show that the oxygen uptake per CeO 2 is highest at the lowest CeO 2 concentration The TPR traces show that a new oxygen species, probably a molecular oxygen anion, is formed at 25 °C which converts slowly at 500 °C to the capping oxygen anion Complete restoration of all three types of oxygen anions is accomplished at 850 °C in air
1,647 citations
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TL;DR: In this paper, it is shown that incorporation of ZrO2 into a solid solution with CeO2 strongly promotes bulk reduction of the Rh-loaded solid solutions in comparison to a Rh/CeO2 sample.
Abstract: Temperature-programmed reduction in a H2/Ar mixture of Rh-loaded CeO2-ZrO2 solid solutions with a ZrO2 content varying between 10 and 90% mol and of monoclinic, tetragonal, and cubic structures is reported. It is shown that incorporation of ZrO2 into a solid solution with CeO2 strongly promotes bulk reduction of the Rh-loaded solid solutions in comparison to a Rh/CeO2 sample. The promotion of the bulk reduction results in high oxygen storage capacity (OSC) as measured by oxygen uptake. A structural dependence of both reduction and oxidation processes is observed which is attributed to a higher oxygen mobility in the cubic structure compared to the tetragonal and monoclinic ones.
831 citations
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TL;DR: In this paper, the reduction of CeO2 by hydrogen has been studied from 300-1200 K by several complementary techniques: temperature-programmed reduction (TPR), magnetic susceptibility measurements, Fourier transform infrared (FTIR), UV-VIS diffuse reflectance and X-ray photoelectron (XP) spectroscopy.
Abstract: The reduction of CeO2 by hydrogen has been studied from 300–1200 K by several complementary techniques: temperature-programmed reduction (TPR) and magnetic susceptibility measurements, Fourier-transform infrared (FTIR), UV–VIS diffuse reflectance and X-ray photoelectron (XP) spectroscopy. Two CeO2 samples were used with B.E.T. surface areas of 115 and 5 m2 g–1, respectively. The concentration of Ce3+ was determined in situ by measuring the magnetic susceptibility and the CeIII photoemission line. The reduction began at 473 K, irrespective of the initial surface area of the ceria. In the case of the low-surface-area sample, an intermediate reduction step was observed between 573 and 623 K, corresponding to the reduction of the surface. This intermediate step was less easily observed in the case of the high-surface-area ceria. In both cases, the reduction led to a stabilised state with the formal composition CeO1.83. Temperatures higher than 923 K were required to reduce the ceria further. The surface CeIII content determined by XPS was close to that determined by magnetic susceptibility measurements. The intensity of the 17 000 cm–1 band in the UV–VIS reflectance spectrum also varied with the degree of reduction. Finally, the evolution of the surface species observed by IR spectroscopy was in good agreement with the results from the other techniques. The IR results indicated large changes in the concentration and nature of both the hydroxyl and the polydentate carbonate species during the reduction process. The adsorption of oxygen on samples previously reduced to the composition CeO1.83 led to almost complete reoxidation at room temperature. The state of the initial B.E.T. surface did not influence the oxidation process. A slight excess adsorption of oxygen was evident on the surface. This was thermodesorbed at 380 K under vacuum.
553 citations