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Journal ArticleDOI

NO decomposition over partially reduced metallized CeO2-ZrO2 solid solutions

01 Mar 1994-Catalysis Letters (Baltzer Science Publishers, Baarn/Kluwer Academic Publishers)-Vol. 24, Iss: 1, pp 107-112
TL;DR: Incorporation of ZrO2 into a solid solution with CeO2 strongly enhances the reducibility of the Ce4+ in the metallized samples and favours an effective NO decomposition over the reduced catalysts.
Abstract: Incorporation of ZrO2 into a solid solution with CeO2 strongly enhances the reducibility of the Ce4+ in the metallized samples and favours an effective NO decomposition over the reduced catalysts.
Citations
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Journal ArticleDOI
TL;DR: A survey of the use of cerium oxide and CeO2-containing materials as oxidation and reduction catalysts is presented in this paper, with a special focus on catalytic interaction with small molecules such as hydrogen, carbon monoxide, oxygen, and nitric oxide.
Abstract: Over the past several years, cerium oxide and CeO2-containing materials have come under intense scrutiny as catalysts and as structural and electronic promoters of heterogeneous catalytic reactions. Recent developments regarding the characterization of ceria and CeO2-containing catalysts are critically reviewed with a special focus towards catalyst interaction with small molecules such as hydrogen, carbon monoxide, oxygen, and nitric oxide. Relevant catalytic and technological applications such as the use of ceria in automotive exhaust emission control and in the formulation of SO x reduction catalysts is described. A survey of the use of CeO2-containing materials as oxidation and reduction catalysts is also presented.

3,077 citations

Journal ArticleDOI
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

Journal ArticleDOI
TL;DR: In this article, the authors illustrate the technology for abatement of exhaust emissions by analysing the current understanding of TWCs, the specific role of the various components, the achievements and the limitations.

1,187 citations

Journal ArticleDOI
TL;DR: In this paper, the authors review the catalytic reactions for the removal of NO and discuss the reduction of NO in the presence of NH3, CO, H-2 or hydrocarbons as well as the decomposition of NO.

1,110 citations

Journal ArticleDOI
TL;DR: In this paper, a low temperature (500°C) route for calcination of hydroxide precipitates and firing mixtures of acetates was investigated and the results showed that the addition of zirconia increased the oxygen storage capacities over ceria alone for both preparation methods.
Abstract: CeO 2 and CeO 2 /ZrO 2 supports were prepared by two low temperature (500°C) routes: calcination of hydroxide precipitates and firing mixtures of acetates. The supports were loaded with 0.5% Pt and characterized both fresh and aged (at 800 and 1000°C). X-ray diffraction analyses show that a CeO 2 /ZrO 2 solid solution is formed in the samples prepared by precipitation of the hydroxides and calcination at 500°C. To our knowledge this is the lowest temperature chemical route (not including high energy ball milling) to CeO 2 /ZrO 2 solid solutions yet reported. Samples prepared by firing the acetate mixtures had almost exclusively CeO 2 and ZrO 2 in separated phases. Oxygen storage measurements showed that the addition of zirconia increased the oxygen storage capacities (on a per gram of catalyst basis) over ceria alone for both preparation methods. In the phase separated materials the amount of reversibly stored oxygen was 1.7–2.5 times more per gram catalyst than that of ceria only. The beneficial effects of zirconia are most pronounced in the solid solutions which had oxygen storage 3–5 times higher than ceria. When the Zr concentration is optimized, the solid solution materials aged at 1000°C showed higher oxygen storage than fresh CeO 2 . For both preparation methods, the optimal (per gram catalyst) Zr concentration was found to be 25 mol% Zr for samples aged at 1000°C, however, the performance of the solid solution materials was somewhat insensitive to Zr loading between 15 and 50 mol% Zr.

492 citations

References
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Journal ArticleDOI
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.

1,726 citations

Journal ArticleDOI
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.

577 citations

Journal ArticleDOI
TL;DR: In this article, the specific activity for NO reduction was found to be sensitive to the nature of the catalyst pre-treatment, and the rate-limiting step in this model was assumed to be the dissociation of chemisorbed NO.

263 citations

Journal ArticleDOI
TL;DR: In this article, the activity of Pt,Rh,Ce/γ-Al2O3 and Pt, Rh/CeO2 catalysts has been studied in a full complement synthetic exhaust gas mixture consisting of H2, CO, C3H6,C3H8, NO, O2, N2, H2O, and SO2.

234 citations