Perovskite reaction with

Good results are obtained with oxide-coated valve metals as anode materials. These electrically conducting ceramic coatings of p-conducting spinel-ferrite (e.g., cobalt, nickel and lithium ferrites) have very low consumption rates. Lithium ferrite has proved particularly effective because it possesses excellent adhesion on titanium and niobium [26]. In addition, doping the perovskite structure with monovalent lithium ions provides good electrical conductivity for anodic reactions. Anodes produced in this way are distributed under the trade name Lida [27]. The consumption rate in seawater is given as 10 g A ar and in fresh water is... 

Proton conduction at high temperatures occurs in certain perovskites such as doped strontium cerate, Sr Ceo.95Ybo.o503 t. In air, this material is primarily an electronic conductor due to the mixed valence of Ce. In the presence of moisture, water is absorbed by the reaction with positive holes to generate protons ... 

This work suggests that the high activity and selectivity of the catalysts Gd-Co-O and Sm-Co-O for the partial oxidation of methane to synthesis gas is due to the stability of the cobalt in its reduced state over the sesquioxides Gd,0, and Sm,0,. In the case of La-Co-O and Nd-Co-O reoxidation of cobalt to the original perovskite structure causes loss of activity and selectivity. TPO experiments with reduced Ln-Co-0 (Ln = La, Nd, Sm and Gd) catalysts indicated that reoxidation takes place in two steps first oxidation of the supported Co to the spinel Co,04 (Co- Co, 04) and further the oxidation of the Co-" to Co with a simultaneous solid state reaction with Ln,0, regenerating the perovskite structure. It was observed that the temperature for the second oxidation step is strongly dependent on the nature of the lanthanide increasing in... 

Another article concerning liquid-phase reactions catalyzed by perovskites is that by Sugunan and Meera (1995). They studied the reduction of ketones and oxidation of alcohol using RBO3 (R = La, Pr or Sr, B = Cr, Mn, Co or Ni) perovskites. Their goal was, however, to correlate data from these test reactions with surface electron-donor properties of these oxides. The electron-donor properties were investigated by the adsorption of electron acceptors with different electron affinities such as para- and /n-dinitrobenzene, benzoquinone, etc. They adsorbed these electron acceptors on both the mixed and the individual oxides. The results obtained are not conclusive to explain the catalytic behavior of the solids studied on the basis of this single property, as is often the case in many catalytic systems. 

The cathode must also display good electrocatalyst activity for the reduction of O2 and offer good electronic conductivity, since it must serve as the current collector. The cathode material most commonly used is porous or mesoporous perovskite manganite with the formula Lai xSr cMn03 (0.10cathode reaction is as follows ... 

An example of a complex material used in syngas applications is Lag jSro gFeo g. Coo.iCro.203 [26]. This composition contains many of the features previously discussed. It is predominately an iron-based perovskite, providing both electronic and ionic conductivity. In order to improve the chemical stability and resistance to chemical expansion, the B-site is doped with chromium. A small amount of cobalt is added in order to improve the electronic conductivity, and cobalt wiU also increase the ionic conductivity slightly. Strontium is used as the A-site dopant in order to avoid the problems associated with calcium, and particularly with barium, in regard to reaction with CO2. In addition, the material has been made substantially A-site deficient to improve its stability. 

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