Rare earths conversion rates

Conversion Rates for Self-Supported Rare Earths and Fractional Rate Changes at 29S K in a Field of 18 kOe... 

The unique luminescent properties of rare earth metal clathrochelates have been used in the development of luminescent materials (luminophores and laser materials). The luminescence of these clathrochelates in solution makes their application as biological probes and concentrators of the luminescence (i.e., the antenna effect ) promising. These complexes can also serve as efficient molecular devices to convert UV light absorbed by the ligand to lanthanide ion luminescence in the visible region. Even in very dilute (10-5 mol l-i) solutions, the conversion of irradiated photons to luminescent ones has been observed to occur at a rate of approximately 1%. For rare earth metal aqua ions at the same concentration, the efficiency of conversion is equal to 4 x IQ- % [212, 390-392]. 

The direct oxidation of propylene by molecular oxygen is a low-selective reaction. The propylene oxide yield can be raised by limiting the conversion rate to a low value, about 10 to 15 per cent, by using more selective catalysts, or by achieving co-oxidation with a more oxidizable compound than propylene (acetaldehyde, isobutyraldehyde etc.). Many patents have been Hied concerning this process, but without any industrial implementation. Among them is the liquid phase oxidation of propylene on a rare earth oxide catalyst deposited on silica gel (USSR), or in the presence of molybdenum complexes in chlorobenzene or benzene (JFP Instiiut Francois du Petrole. Jefferson ChemicalX vapor phase oxidation on modified silver catalysts (BP British Petroleum IFP, or on ... 

The excited-state lifetime of the molecule in absence of any radiationless deeay processes is the natural fluorescence lifetime", r . The natural lifetime is a constant for a given molecule and given refraction index of the solvent. Because the absorbed energy can also be dissipated by internal conversion, the effective fluorescence lifetime, is shorter than the natural lifetime, The fluorescence quantum efficiency", i.e. the ratio of the number of emitted photons to absorbed photons, reflects the ratio of the radiative decay rate to the total decay rate. Most dyes of high quantum efficiency, such as laser dyes and fluorescence markers for biological samples, have natural fluorescence decay times of the order of 1 to 10 ns. There are a few exceptions, such as pyrene or coronene, with lifetimes of 400 ns and 200 ns, and rare-earth chelates with lifetimes in the ps range. 

Since there are many transition metal and rare earth oxides with two or more stable valencies, there would seem to be many candidates available for buffering the A/F oscillations in the gas phase. Yet only one, cerium oxide, has achieved widespread use. Were it not for ceria, the TWC strategy could never be implemented. The key, as noted above, is the rate of interconversion between oxidation states. Perturbation frequencies on cars are in the vicinity of 1 Hz. The OSC (oxygen storage capacity) component must keep up with this if it is to contribute to conversion. This means that both oxidation and reduction must be rapid. 

Multiphonon decay rates from excited states of rare earth ions determine three important properties of rare-earth lasers pump conversion efficiency,... 

Vernon et al tested a series of noble metal catalysts, either Ru, Rh, Pt, Pd or Ir supported on AI2O3, or rare earth ruthenium pyrochlore materials. All materials yielded the equilibrium CPO conversion of methane to syngas at IITC and 1 atm. After the reaction, it was found that Ru had been reduced out of the pyrochlore structures. Claridge et al. studied coke formation over alumina-supported or pyrochlore-derived catalysts and reported that the coke forming rates decreased in the order Ni > Pd > Rh > Ir, as illustrated in Fig. 8.3. ... 

---