Perovskites catalytic properties

The special electric, magnetic, optical, superconductive and catalytic properties of perovskite-typed oxides make this group of materials attracting and widely used. Perovskites were named according to the similarity of their structure with the CaTiOs compoimd. The... 

Ciambelli, P Cimino, S Lisi, L Faticanti, M Minelli, G Pettiti, 1 Porta, P. La, Ca and Fe oxide perovskites preparation, characterization and catalytic properties for methane combustion. Appl Catal, B Environmental, 2001, Volume 33, Issue 3, 193-203. 

Szabo, V Bassir, van Neste, A Kaliaguine, S. Perovskite-type oxides synthesized by reactive grinding Part II. Catalytic properties of LaCoi.xFcxOs in VOC oxidation. Appl. Catal. B Environmental, 2002, Volume 37, I75-I80. 

The basic perovskite structure ABX3 forms the prototype for a wide range of other structures related to it by combinations of topological distortions, substitution of the A, B and X ions, and intergrowth with other structure types. These compounds exhibit a range of magnetic, electrical, optical, and catalytic properties of potential application in solid state physics, chemistry, and materials science. 

RE2CUO4 perovskites exhibit important and varying magnetic and electrical characteristics, and they are broadly studied as potential high-Tc superconductive materials. At room temperature, they show p-type semiconducting behaviors, and are used as electrode materials in fuel batteries. The catalytic properties of the perovskite oxides also make them effective in various oxidation and reduction reaction, hence they are considered as promising substitutes to the classical Pt/Rh-based catalysts applied to automotive pollution control. 

J.L.G. Fierro, Structure and composition of perovskite surface in relation to adsorption and catalytic properties, CataL Today 5 153 (19%). 

H.-M. Zhang, Y. Shimizu, Y. Teraoka, M. Miura and N. Yamazoe, Oxygen sorption and catalytic properties of Lai-xSrxCoi-yFcyOs-s perovskite-type oxides. /. Catal., 121 (1990) 1367-1370. 

Figure 1 presents the dependence of the catalytic activity and isobutane selectivity of samples precipitated at pH = 9 on the CaO concentration. This study made it possible to evaluate the role of the cubic solid solution in their catalytic properties. One can see an obvious maximum on the dependence of the activity on the alkaline earth metal concentration in the structure of Zrj.xCaxOz-x solid solution. Without calcium the catalytic activity is low. This agrees with the literature data that sulfation of a calcined monoclinic phase without any special treatment does not yield an active catalyst [9]. The maximum activity is observed for the samples with the CaO concentration of 5-10 mol.%. The material with the calcium concentration of 50 mol.% does not show any catalytic activity at all. This sample is mostly composed of perovskite crystalline phase CaZrOs. A comparison of the catalytic activity of the samples with their surface areas clearly indicates that the activity growth is mostly caused by the formation of the cubic phase rather than just by an increased surface area. 

L.A. Isupova, S.V. Tsybulya, G.N. Kryukova, G.M. Alikina, N.N. Boldyreva, A.A. Vlasov, O.I. Snegurenko, V.P. Ivanov, V.N. Kolomiichuk, V.A. Sadykov, Physicochemical and catalytic properties of Lal-xCaxFeO3-0.5x Perovskites prepared using mechanochemical activation, Kinet. Catal. 43 (2002) 129. 

A number of methods have been used in the synthesis of perovskites the choice of a particular one depends mostly on the expected use for these oxides. Obviously, no attention has been paid to textural characteristics of samples whose uses are based on their electric or magnetic properties. However, application of perovskites in the field of catalysis requires solids with a well-developed porous network. As the present review is concerned particularly with the surface and catalytic properties of perovskites, we will place special emphasis on preparation methods leading to a high surface volume ratio. Also, methods yielding homogeneous solids will be discussed because of the important effect that inhomogeneities may play in heterogeneous catalysis. 

Catalytic Properties of Strontium Ruthenate Perovskite Prepared by Hot Isostatic Pressure Method... 

Ruthenium has always been considered as one of the most active catalysts for several reactions of commercial and environmental importance. In early seventies, ruthenium was studied for its possible application as a de-NOx catalyst for automobiles. Its volatile nature in oxide form was soon realized and efforts were directed to stabilize ruthenium, without much affecting its catalytic properties. Attempts were also made towards synthesis of mthenium based perovskite t3 e and other mixed oxide compositions, as the incorporation of ruthenium in perovskite structure can substantially improve its thermal stability... 

Some of the many different types of catalysts which have good catalytic properties for the OCM reaction qualify as membrane materials. Membrane reactors for OCM were designed and tested by Nozaki et al. (1992). Three kinds of reactors were developed the first one consisted of a porous membrane covered with a thin film of catalyst (type I) the second one, a dense ionic-conducting membrane (non porous) with catalytic layer (type II) and the third one was a membrane made of perovskite-type mixed oxides which was active for OCM (type III). Figure 11 presents the diagram for the membrane reactor system and table 13 shows the different materials used for supports and coated catalysts. 

Ammonia oxidation was the test reaction chosen by Yu et al. (1992) to investigate connections between structure and catalytic properties in Lai- Sr NiC and Lai i 33iThxNi03 For x < 0.3, both types of solids only showed the reflections corresponding to the perovskite structure. At x 0.3, several other phases appeared, i.e. NiO, La2Ni04 and Th02. As the Sr concentration increases, the number of oxygen... 

An interesting example of the application of perovskites as electrodes was published by Muller et al. (1994). Lao.6Cao4Co03 has excellent catalytic properties for O2 reduction and evolution as shown by Shimizu et al. (1990). In order to obtain a more durable electrode material, Muller et al. (1994) used graphitized carbon (70 m2/g) as support of the perovskite catalysts. They described in detail the technique used to prepare the electrode which was assayed using an experimental setup adequate for the intended application of this electrode, namely Zn/air batteries. Their main advance over previous formulations was to achieve longer durability of the electrode with some reduction in current density when compared to the previous work of Shimizu et al. (1990). The authors also suggest routes to improve the overall performance of this attractive system. 

The most important catalyst systems involving rare earth elements are the oxides and intermetallics. Catalytic properties of rare earth oxides are described in section 4 and those of intermetallic compounds in section 6. Reports on surface reactivities of other binary rare earth compounds are only sparse, and this is mentioned in section 5. A very interesting class of catalyst systems comprises the mixed oxides of the perovskite structure type. As catalysis on these oxides is mainly determined by the d transition metal component and the rare earth cations can be regarded essentially as spectator cations from the catalytic viewpoint, these materials have not been included in this chapter. Instead, we refer the interested reader to a review by Voorhoeve (1977). Catalytic properties of rare earth containing zeolites are, in our opinion, more adequately treated in the general context of zeolite catalysis (see e.g. Rabo, 1976 Katzer, 1977 Haynes, 1978) and have therefore been omitted here. 

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