Ce oxides

The various cerium-containing derivatives available commercially are summari2ed in Table 3. The 1991 prices, per kg of contained Ln oxide, ie, not necessarily Ce oxide, range from about 3 for types A and B, ca 5 for type C, ca 12 type D, and ca 25 for type E. 

Clearance to pulmonary lymph nodes will occur at a fractional rate of 0.0001 per day. Dissolution of the deposited particles and absorption of cerium into the systemic circulation will occur at rates that are between the extremes represented by CeCh in CsCl particles and Ce oxide or Ce in fused aluminosilicate particles as given by the functions included in Figure 9. These rates should not be expected to be constant over the entire clearance period and will depend upon the overall composition of the bulk aerosol particles, which indude particle size, amount of stable lanthanide present, acidity, and the solubility of other components of the particles. The accuracy of predicting respiratory tract clearance and internal organ uptake of radiocerium will depend heavily upon adequate determination of the particle solubility characteristics. 

Figure 10.7 Influence of sur ce oxidation and pretrcatinent on self-induced flotation of galena and chalcopyrite. Galena 1-untreated 2-pretreated by ultrasonic wave, chalcopyrite 3-aged two month 4-pretreated by ultrasonic wave (Wang et al., 1991a,b,c,d)...

Early in the nineties Ruiz et al. reported enhanced catalyst activities and increased selectivities to alkenes and higher hydrocarbons upon addition of V, Mg, and Ce oxides to Co-based F-T catalysts.These variations were attributed to electronic effects induced by the transition metal oxide. Similar results were obtained by Bessel et al. using a Cr promoter in Co/ZSM-5 catalysts.This group observed that the addition of Cr improved the catalyst activity, and shifted the selectivity from methane to higher, generally more olefinic, hydrocarbons. Based on H2 and CO chemisorption, as well as TPR and TPD results, they suggested that the promotion was caused by an interaction between the transition metal oxide and the cobalt oxide, which inhibits... 

Significant improvement of the activity of selectivity of Pd on Si02 could be achieved in the hydrogenation of acetylene by adding Ti, Nd, or Ce oxides to the catalyst.395 The metal oxides modify both geometrically and electronically the Pd surface. They retard the sintering of the dispersed Pd particles, suppress the formation of multiply bound ethylene, and facilitate the desorption of ethylene. The beneficial effect of lead in the hydrogenation of 1,3-butadiene over a Pd-Pb-on-... 

The detailed mechanism for the formation of reduced Cu+ species under the hydrothermal synthesis conditions in the presence of CTAB without any additional reducing reagent is not clear at present, but the degree of reduction of the Cu- and oxide-precursors may depend on the oxophilicity of metal oxides Cu oxide (most reducible) < Mo oxide < Zn oxide < Si oxide < A1 oxide Zr oxide Ce oxide (hard to reduce). Further, chemical interaction of the Cu + clusters with the Ce02 surface may also be the key to stabilizing the Cu + clusters on the support. 

Table 2.2 shows the catalytic performances of various Cu and Ce catalysts for CO PROX reactions in excess H2 at 90 °C. Ce oxides, Ce-CTAB and Cu-CTAB were completely inactive for CO oxidation at 90 °C. In contrast, the hydrothermally-prepared Cu/Ce-CTAB catalyst (7.5 wt%Cu) exhibited good catalytic performance for the CO PROX, with 91.9-96.1% CO conversion and 99.4—99.8% 02 selectivity at 90°C in a feed of C0/02/H2= 1 1 50 (Table 2.2). Table 2.3 summarizes the performance of the Cu/Ce-CTAB catalyst under various reaction conditions, different W/F, reaction temperatures and feed compositions. Notably, high CO conversions and 02 selectivities were also achieved in reactant feeds containing substantial amounts of H20 and C02. The CO conversions and 02 selectivities at W/F = 2.24 gcath mol-1 and 90 °C were 85.7% and 98.7%, respectively when H20 (10%) existed, and 81.4% and 98.2%, respectively when H20 (10%) and C02 (20%) co-existed. 

Alouche et al. studied the selective hydrogenation of rapeseed oil over reduced Ni-Ce oxides and the effects of aluminum incorporation to them. The binary Ce-Ni oxide presented a good selectivity in the partial hydrogenation, as studied in a flow system at temperatures of 190-250°C, but with a large 7JE isomerization. On the other hand, use of ternary Ce-Ni-Al oxides [e.g., Ce/Al = 1, Ni/(Ce + Al) = 5], prepared from the nitrates of cerium, nickel, and aluminum by coprecipitation using potassium hydroxide, allowed a decrease in the extent of the 7JE isomerization.100... 

Answer 4.10 Ln /3-diketonates are often coordinatively unsaturated (Section 4.3.4) and tend to polymerize. The molecular nature of the Ce compounds should confer greater volatility, as well as solubility in nonpolar solvents (e.g. petrol). The Ce oxidation state may also assist the oxidation process. 

Np" + is in many ways the most important oxidation state. It is formed by reduction of the higher oxidation states, and by aerial oxidation of Np +. Strong oxidizing agents like Ce + oxidize it back to [Np02], whilst electrolytic reduction of Np" + affords Np +, which is stable in the absence of air (unlike U). 

Ce species formed upon reduction of Ce02 are known to be reoxidized quickly by exposure to even small O2 pressures [127] this easy Ce oxidation was observed even for the (highly amorphous) hydroxides which appear in the first stages of preparation via precipitation [128], It is thus striking that nanocrystalline... 

Of major concern for ceria based catalysts is the reducibility of the ceria support. Several papers mention experiments related to this subject. For model surfaces it is possible to quantitatively determine an average oxidation state of the ceria film, i.e. the ratio of Ce / Ce This is most commonly done using XPS of the Ce 3d photoemission features. The 3d spectrum is complicated by satellite features which are well described and provide useful variation with Ce oxidation state. ... 

Bau M. (1999) Scavenging of dissolved yttrium and rare earths by precipitating iron hydroxide experimental evidence for Ce oxidation, Y-Ho fractionation and lanthanide tetrad effect. Geochim. Cosmochim. Acta 63, 67-77. 

When Ce(III)Y zeolites are calcined under oxygen at 400°-500°C, they turn pale yellow, probably by Ce " oxidation to Ce ". Adsorption of anthracene on these samples gives rise to a strong EPR signal. The same spectrum was observed by Rooney and Pink on silica-alumina (JS) and interpreted as arising from an anthracene positive radical. 

Related to this is the observation that Ce oxidation of, for example, 9,10-DMA in MeOH-MeCN at 0°C leads exclusively to the 9,10-adduct, XIX, which upon heating to 45°C was converted to the side chain oxidation product, XX, by elimination of MeOH. 

Without catalyst, phenol conversion is less than 3% at 140°C at a pressure of 2.0 MPa of oxygen. In addition, a test with 50 mg/1 of Mn" (quantity eluted when an experiment is run with 4 g/1 of Mn-Ce oxide) gives a phenol conversion of lower than 3%. This confirms that the formation of carbon deposit is heterogeneous. 

Mn-Ce oxide catalysts are very active in wet air oxidation of phenol. However, formation of polymer during reaction is a great drawback which limits its application. The same phenomenon has been observed with copper based catalysts. Further studies to control the processes by which... 

A homogeneous catalyst exists in the same phase as the reactants. Ceric ion, Ce4+, at one time was an important laboratory oxidizing agent that was used in many redox titrations (Section 11-8). For example, Ce + oxidizes thallium(I) ions in solution this reaction is catalyzed by the addition of a very small amount of a soluble salt containing manganese(II) ions, Mn +. The Mn + acts as a homogeneous catalyst. 

The Sr-Ce oxides were stable at 600-800°C when H2O was added in the streams of anode and cathode. The addition of H2O was necessary in order to maintain protonic conduction through the ceramic electrolyte [4]. However, it is known that Sr-Ce oxides decomposed to SrCOs and CeO2 at high CO2 atmosphere [12]. Therefore, the use of the Sr-Ce oxide is not proper under the condition of CO2 atmosphere. In the present study, gas composition detected in the exhaust from the anode was CH4, H2, H2O, and CO. No CO2 was observed throughout the present study. This may be because the reaction temperature was higher than 600°C, and a sufficient amount of H2O was supplied to the anode and cathode. There was high possibility of production of CO2 at lower temperatures of 300-500°C [7]. The use of a compact Ni electrode in place of the porous Ni/SiO2 electrode may be proper if CO2 is... 

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