Ceria incorporation

Granger, P., Delannoy, L., Lecomte, J.J. et al. (2002) Kinetics of the CO + NO Reaction over Bimetallic Platinum-Rhodium on Alumina Effect of Ceria Incorporation into Noble Metals, J. Catal., 207, 202. 

The textural nature of the titania and TiCex were characterised by nitrogen ad/desorption isotherms. The specific surface areas are presented in Table la. None of the materials were found to be microporous from t-plot analyses of the adsorption isotherms. From the desorption curves, the mesopore size distribution was calculated using the BJH method. All of the samples had bimodal mesopore size distributions. The volumes of the narrow and wide mesopores, presented in Table lb), were calculated from the minima between the two distributions. These results indicated, that as the amount of ceria incorporation rose, the bimodal mesopore size distribution became narrower. For the titania sample the mesopores were centred in diameters of approximately 14 and 17 nm. With ceria incorporation both of these diameters were reduced until at the highest ceria content they were approximately 9 and 15 nm. 

For the monolithic samples the presence of the inorganic binder tended to mask the differences between samples due to its high surfece area. However, analysis of the pore size distribution fi-om the nitrogen isotherm of the material with no ceria, showed the characteristic diameters for the titania at 14 and 17 nm and a fiuther diameter at about 48 nm associated with the binders. With ceria incorporation the pores at about 48 nm were unchanged but the narrower pores due to the titania were reduced to 9 and 17 nm then to 9 and 15 nm at 2 and 4% respectively. These changes in the pore size distribution of the monolithic samples suggested that the ceria was associated with the titania and not with the binders, in agreement with the results fi om EMPA-WDS line profiles. 

The effect of ceria incorporation in NM/AI2O3 washcoat on the NO reduction by CO or hydrocarbons was extensively investigated in past and recent studies [6,34,35], since this reaction is of major importance in three-way chemistry involving the simultaneous removal of two automotive pollutants. As in the case of CO oxidation, proposed reaction mechanisms reveal the important role of the metal-Ce02 interfacial sites on the substantial promotion found to be at work on the aforementioned catalytic system. 

In an actual exhaust system controlled by the signal of the oxygen sensor, stoichiometry is never maintained, rather, it cycles periodically rich and lean one to three times per second, ie, one-half of the time there is too much oxygen and one-half of the time there is too Httle. Incorporation of cerium oxide or other oxygen storage components solves this problem. The ceria adsorbs O2 that would otherwise escape during the lean half cycle, and during the rich half cycle the CO reacts with the adsorbed O2 (32,44,59—63). The TWC catalyst effectiveness is dependent on the use of Rh to reduce NO and... 

Fuel sulfur is also responsible for a phenomena known as storage and release of sulfur compounds. Sulfur oxides (S02,S02) easily react with ceria, an oxygen storage compound incorporated into most TWC catalysts, and also with alumina. When the air/fuel mixture temporarily goes rich and the catalyst temperature is in a certain range, the stored sulfur is released as H2S yielding a rotten egg odor to the exhaust. A small amount of nickel oxide incorporated into the TWC removes the H2S and releases it later as SO2 (75—79). 

Ronning, Holmen, and coworkers—Ce doping of Cu/Zn/Al catalysts improves stability. Ronning et al,339 explored the impact of ceria addition to Cu/ZnO catalysts. Catalysts were prepared by co-precipitation of Cu, Zn, and Al from their corresponding nitrates. Ceria was incorporated into the catalyst by impregnation of cerium nitrate either before or after calcination (6 hours at 350 °C or 400 °C). The chemical compositions of the resulting catalysts are reported in Table 62. 

G. Wrobel, C. Lamonier, A. Bennani, A. D Huysser, and A. Aboukais, Effect of incorporation of copper or nickel on hydrogen storage in ceria Mechanism of reduction, J. Chem. Soc. Faraday Trans. 92, 2001-2009 (1996). 

As an example. Figure 54a shows the zero-bias impedance of LSC electrodes on rare-earth-doped ceria in air at 750 °C measured using a symmetric cell incorporating a traditional reference electrode. Although the two screen-printed electrodes (1 and 2) were processed identically and aligned to an accuracy of 0.1 mm, the cell response is highly asymmetric... 

As discussed in previous sections, Cu acts primarily as an electronic conductor within the Cu-based anodes. Because it is a poor catalyst for C—H and C—C bond scission, it is essential to incorporate an oxidation catalyst, ceria, within the anode. While Ni has many attractive properties, its propensity for catalyzing carbon formation prevents its use in dry hydrocarbons at high temperatures. One approach for enhancing the catalytic properties of Cu and stabilizing the tendency of Ni for forming carbon is to use Cu—Ni alloys. Cu—Ni alloys have been used... 

Zhang et al. reported a nanocomposite membrane of shuttle shaped ceria nanocrystals (Guo et al., 2008), SWNTs, and ILsl-butyl-3-methyli-midazolium hexafluorophosphate (BMIMPFg), which was incorporated on the glassy carbon electrode for electrochemical sensing of the immobilization and hybridization of DNA (Zhang et al., 2009). The electron transfer resistance (Pgt) of the electrode surface increased after the immobilization of probe ssDNA on the Ce02-SWNTs-BMIMPF6 membrane and rose further after the hybridization of the probe ssDNA with its complementary sequence. 

The mixture of these effects described above is obtained by the doping of rare earths elements with variable oxidation state. For example, incorporation of terbium or praseodymium increases both oxygen desorption at lower temperatures and the creation of oxygen vacancies than those of pure ceria. The former is due to the lower binding energy of a lattice oxygen in the mixed oxides and the latter is to the existence of irivalent terbium and praseodymium ions. In addition, a similar effect is also provided by the ternary oxides Cco6Zro4.iM 02. >2 (M = La, and Ga ), ... 

The formation of solid solutions is not the only way to modify the redox property of ceria, TTie incorporation of small amounts of silica in a form of ceria-... 

As deduced from the magnetic balance results commented on above, also confirmed by XAS data (205), the use of chlorine-containing metal precursors may deeply modify the redox properties of ceria. The reversible contribution plays a minor role, thus suggesting that the presence of chlorine heavily disturbs the H2-CeC>2 interaction (209). This has also been confirmed by some volumetric (209) and TPD studies (166), Likewise, the above results show the existence of a new very important contribution to the total reduction degree reached by ceria. It is specifically related to the Cr ions incorporated into the ceria lattice. Though it does not revert on outgassing, no oxygen vacancies would be associated with this third contribution (52,163,193,195). 

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