Bulk lanthanide oxides

Lanthanide oxides as the bulk phase supporting dispersed metals For synthesis gas (CO-H2) reactions... 

While Cu can be utilized as a catalyst, it does not contribute significantly to the overall catalytic activity of the anode. This was verified by the low performance of Cu-only anodes, particularly in hydrocarbon fuels [22], and the identical performance achieved when Cu is replaced with catalytically inert bulk Au [41]. The role of Ce02 as electrocatalyst for fuel oxidation was confirmed by replacing Ce02 with other lanthanide oxides and comparing SOFC performance with the activity of the lanthanide toward fuel oxidation [22]. The ceU performance tracked well with the M-C4H10 light-off temperature of the lanthanide. 

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. 

In the soil the lanthanides are immobile under a wide variety of pH conditions, due to the low solubility of salts such as carbonates and phosphates. ConcenU ations in ground water are much lower than those of the soil through which the water percolates. In most natural waters, because the lanthanides sorb strongly to silicates and humic material, the bulk of the Ln content including cerium is associated with such colloidal particulates [44]. In the marine environment a depletion of cerium relative to the other lanthanides is found that is attributed to the oxidation of cerium (III) to highly insoluble Cc(IV) (OHjj-type species. 

Organolanthanide(III) compounds form the bulk of all the known organo-lanthanides. However, in addition to the + 3 oxidation state, the + 2 oxidation state is chemically accessible for samarium, europium and ytterbium (an organocerium(II) [1] and an organoneodynium(II) [2] complex have also been reported but not structurally confirmed) and the +4 oxidation state is accessible for cerium. A few organolanthanide(O) compounds are also known,... 

Structural, physical and chemical properties of bulk rare earth oxides can be found in Chapter 27, Volume 3 of this series and have been compiled with a view towards catalysis in a recent review by Rosynek (1977). An important parameter for the catalytic behavior of rare earth oxides is their basicity. The basicities of rare earth oxides resemble those of the alkaline-earth oxides, and scale directly with the respective cation radii. Thus, La203 shows the strongest basicity and SC2O3 the weakest, with sesquioxide basicities decreasing smoothly along the lanthanide series going from La to Lu. This periodic trend allows one to study the influence of subtle variations in basicity on catalytic behavior in a class of related materials with similar electronic and geometrical structure. 

The term upconversion describes an effect [1] related to the emission of anti-Stokes fluorescence in the visible spectral range following excitation of certain (doped) luminophores in the near infrared (NIR). It mainly occurs with rare-earth doped solids, but also with doped transition-metal systems and combinations of both [2, 3], and relies on the sequential absorption of two or more NIR photons by the dopants. Following its discovery [1] it has been extensively studied for bulk materials both theoretically and in context with uses in solid-state lasers, infrared quantum counters, lighting or displays, and physical sensors, for example [4, 5]. Substantial efforts also have been made to prepare nanoscale materials that show more efficient upconversion emission. Meanwhile, numerous protocols are available for making nanoparticles, nanorods, nanoplates, and nanotubes. These include thermal decomposition, co-precipitation, solvothermal synthesis, combustion, and sol-gel processes [6], synthesis in liquid-solid-solutions [7, 8], and ionothermal synthesis [9]. Nanocrystal materials include oxides of zirconium and titanium, the fluorides, oxides, phosphates, oxysulfates, and oxyfluoiides of the trivalent lanthanides (Ln ), and similar compounds that may additionally contain alkaline earth ions. Wang and Liu [6] have recently reviewed the theory of upconversion and the common materials and methods used. 

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