Tunnel structures oxides with

Table 1. Crystallographic data for manganese oxides with tunnel structures... 

An efficient oxidation catalyst, OMS-1 (octahedral mol. sieve), was prepared by microwave heating of a family of layered and tunnel-structured manganese oxide materials. These materials are known to interact strongly with microwave radiation, and thus pronounced effects on the microstructure were expected. Their catalytic activity was tested in the oxidative dehydrogenation of ethylbenzene to styrene [25]. 

Another conductivity mechanism could be suggested for LB films of this polymer with Ag+ cations. Such cations can accept or release electrons easily, so in the layer of such cations the conductivity could be caused by electron transitions between the ions with different degrees of oxidation. With tunneling microscopy an anomaly in the dl/dV(V) curves near zero bias was discovered for the LB films in Ag form with an odd number of layers there was a conductivity peak some 150-200 mV wide (Figure 7.4, Curves 1, 3) but no anomaly for these same films with an even number of layers (Figure 7.4, Curve 2). For LB films with an odd number of layers the ordered superstructure of the scale 11.5 x 11.5 x lO cm has been found in a conductivity dl/dV (x,y) measurement regime. The scale of such a structure corresponds to 3 x 2 surface reconstruction (Figure 7.5). 

Leland and Bard (1987) found that the different iron oxides induced photooxidation of oxalate and sulphite at rates that varied by up to two orders of magnitude. For oxalate, the rate was greater for maghemite than for hematite, but this order was reversed for sulphite. Lepidocrocite (layer structure) induced faster oxidation of both compounds that did the other polymorphs of FeOOH (tunnel structures) the authors considered that the rate differences were probably associated with structural differences between the adsorbents. 

In the development of meta oxiae photocata-ysts with high and stable photocatalytic activity for water decomposition, the establishment of a correlation betweer photocatalytically active sites and metal oxide structures is desirable. In particular, it is important to see how the local structures of metal oxides are associated with the essential steps such as photoexcitation, the transfei of excited charges to the surface, and reduction/oxidation of adsorbec reactants. This chapter deals with photolysis of water by titanates with tunnel structures. The roles of tunnel-related local structures ir the photocatalysis and of Ru02 promoters loaded on the titanates are presented. 

Oxides with layered stmcture or those whose structures contain large tunnels or cavities may display abnormal ion movement or serve as templates for heterogeneous catalysis (see Ionic Conductors Intercalation Chemistry Oxide Catalysts in Solid-state Chemistry andZeolites). Many oxides are stabilized by the formation of structures that are highly defective nature and have similar properties to those listed above (see Defects in Solids). The strong bonds, which result in three-dimensional cross-linked structures, give rise to inert, refractory materials that have a variety of uses (see Section 5.3.6 and Ceramics). 

Fig. 14. Top Schematic representation of the corundum unit cell and surface structures with different terminations. Bottom left Scanning tunneling image of the Fe2O3(0001) surface. The darker area is believed to be metal terminated and the brighter area metal terminated according to corundum(0001)-Me [92]. Bottom right List of lattice parameters for different oxides with corundum structure [15].

Vibrations characteristic of Sb—O stretches and deformations have been discussed for solid antimonates such as M Sb03, MnSb206, and M2Sb207.770 Preparation of a new family of mixed oxides with structures related to that of cubic KSb03 has been announced, and the detailed structure of one such compound, Bi3GaSb2On, has been obtained.771 Potassium ion transport can occur through two-dimensional tunnels that occur in the structures of K3Sb5014 and KjSb.On.772... 

Figure 7. Radial distribution functions (RDF), not corrected for phase shift from EXAFS spectra, of sediment-trap material from Lake Sempach and from reference oxides. Pyrochroite, Mn(OH)-, and bimessite [a Mn(IV) oxide] have the same layered structure with edge-sharing Mn octahedra. Todorokite is a Mn(IV) oxide with a 3 X 3 tunnel structure. A shift to longer distances occurs in going from the Mn(IV) oxide bimessite to the Mn(II) hydroxide pyrochroite. Contributions from double-comer Mn-Mn linkages are clearly seen in sediment-trap material and in todorokite and vemadite but not in the layered minerals bimessite and pyrochroite.

The electrochemical reaction leads to a more reduced or more oxidized state in the product than in the molten salt. Only electroreduction has so far been used to prepare compounds with tunnel structures. In such structures the tunnels contain ions, e.g., alkali-metal ions in a transition-metal oxide host lattice. Ionization of the inserted alkali-metal gives electrons to the oxide host, reducing the transition-metal cations. 

Examples of Oxides with Tunnel Structures Obtained by Molten Salt Electrolysis. 

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