Lattice oxygen mobility

With increasing dodecyl amine, the surface area of the catalyst and, hence, the conversion decreased, whereas the selectivities for formation of methacrylic acid and methacrolein increased. The increase in selectivity was ascribed to a reduction in lattice oxygen mobility in the dodecyl alcohol-modified materials, which decreased the amount of COx produced. 

Alfhough for fhe pasf 40 years, vanadium phosphates have been used exclusively for conversions of gas-phase reactants, these catalysts have recently been applied to low-temperature (60-140 °C) oxidations with liquid-phase reactants. It is perhaps surprising that vanadium phosphate catalysts have been used at such low temperatures because they negate one of fhe key feafures of (VO)2P207, fhe lattice oxygen mobility. The lack of... 

Frolova-Borchert et al. fabricated nanocomposites comprised of fluo-rite-like Gd- or Pr-doped ceria and perovskite LaMnOa using Pechini route (Frolova-Borchert, et al., 2006). Interaction between components is reflected in the increase of doped ceria lattice parameters and disordering of Mn coordination sphere. Despite this interaction, nanocomposites possess a high conductiviy and a high lattice oxygen mobility and reactivity. 

One of the most important properties of these OMS and OL systems is their ability to lose and recover oxygen.92, 3,94,95 Temperature programmed desorption, reduction, Oxidation, and studies of lattice oxygen mobility and structural stability studies have been done on a variety of systems. A review of these and similar open framework structures has recently been submitted. 96... 

The nature of oxygen contribution to the oxidation process may be established by using the radioactive tracer technique. The reduction-oxidation mechanism of reactions is a function of the lattice oxygen mobility. Vainstein and Turovskii (86) investigated the distribution of O18 in the oxidation of carbon monoxide over MnOa and CuO and found that there will be no transfer of the catalyst oxygen to the reaction products, when water is carefully removed from the solid oxides. 

O atom(s) insertion(s) from the lattice, and several electron transfers. In the collective properties of solid surfaces, in particular, lattice oxygen mobility and electron conductivity are involved. In general, the oxygen requirement of the selective reactions is less demanding than that of the nonselective reactions. It follows that restricting the availability of lattice oxygen anions around the active site will favor the selective oxidation reactions over the total oxidation reactions. This was clearly demonstrated, for example, for USbsOio catalyst for propene oxidation to acrolein by Grasselli et al. [16,17] several years ago. 

The reducibility and reoxidizability (redox property) of the metal oxide catalyst, electron and lattice oxygen mobilities within the bulk or its upper surface layers. 

In our research we aimed at synthesis of several complex Mn, Ni and Co-containing perovskites via Pechini route, characterization of their transport properties (conduetivity by impedance spectroscopy and oxygen mobility/reactivity by isotope exchange), seleetion the most promising perovskite system for preparation of its nanocomposite with apatite-type electrolyte, synthesis and characterization of this nanocomposite. To minimize effeets of cation exchange between perovskite and apatite-type electrolyte, for composite synthesis Fe-doped La silicate was used. On the bases of a high conductivity and lattice oxygen mobility as well as compatibility by TEC, La-Sr-Fe-Ni-0 (LSFN) perovskite was chosen for eomposite synthesis. 

Hence, both specific catalytic activity in activation of O2 molecules on the surface of LSNF sample and lattice oxygen mobility characterized by isotope exchange apparently meet requirements for cathode material for IT SOFC. 

Dai et al. reported that the presence of F-or Cl-ions in the perovskites promotes lattice oxygen mobility in Laj j Srj FeQ3 thereby reducing the deep oxidation of C H [79]. YBa CujO, , jgCl, 3 catalysts exhibited 68.8% C H yield at a C Hg conversion of 92.5%. An ethylene yield of 55% was observed in the case of a short-contact-time reactor consisting of a LaMnOj based monolithic catalyst below 400°C [80]. Donsi et al., observed that the formation of ethylene was catalyzed by both monolith surfaces and the through gas-phase radical reactions [80]. Alifanti et al. [81] observed that SmCoOj and PrCoOj perovskites were active for ethane ODH even at 300°C i.e., much below the temperature previously reported for perovskites. 

In general, perovskite-like complex oxides Ba(Sr)-Fe(Co)-0 comprised of disordered intergrown perovskite- braunmillerite domains possessing a high lattice oxygen mobility/oxide ionic conductivity demonstrate also not too high (1-10 S/cm) specific total conductivity at 1000 K [97, 98]. 

The possibility of exchange mechanism discrimination is clearly illustrated by Fig. 30, in which the variation of the mole fractions of isotope dioxygen molecules with time is shown for two samples greatly differing by the lattice oxygen mobility. In both cases the initial gas was entirely comprised of the 62 molecules. However, for the Sr-Fe-Co-0 sample (Fig. 30a), asymmetric isotope molecules were not formed while for La-Ca-Mn-0 sample... 

---