Perovskite type oxide catalysts

Manganese oxides have long been known to be catalysts for a variety of gas clean-up reactions. Manganese/copper mbced oxide (Hopcalite) is the catalytically active component in gas mask filters for CO CO is converted to CO2 at room temperature [4]. Further applications of manganese oxide catalysts are the NH3 oxidation to N2 [5], the combustion of VOC [6,7] and methane [8], the oxidation of methanol [7], the O3 decomposition [9] and the NOx reduction [14]. Perovskite-type oxide catalysts (e.g. LaMnOs) have been proven to be effective catalysts for the total oxidation of chlorinated hydrocarbons [10]. Several studies have shown that besides preparation method and calcination temperature the kind... 

IMPROVING THE S02 RESISTANCE OF PEROVSKITE TYPE OXIDATION CATALYST... 

SIMULTANEOUS NOx REDUCTION AND SOOT ELIMINATION FROM DIESEL EXHAUST ON PEROVSKITE-TYPE OXIDE CATALYSTS... 

Schneider R, KieBling D, Wendt G. Cordierite Monolith Supported Perovskite-type Oxides Catalysts for the Total Oxidation of Chlorinated Hydrocarbons. Appl Catal B Environ 2000 28 187-195. 

Mudu, R, Arstad, B. andBakken, E. (2010). Perovskite-type oxide catalysts for low temperature, anaerobic catalytic partial oxidation of methane to syngas, J. Catal., 275, pp. 25-33. 

Kiebling, D., Schneider, R., Kraak, P., Haftendron, M., and Wendt, G. Perovskite-type-oxides-catalysts for the total oxidation of chlorinated hydrocarbons, Catal B Environ. 1998,19, 143-151. 

Table 2. Surface morphologies, BET surface areas, preparation and reaction parameters, and catalytic performance of some perovskite-type oxide catalysts...

Catalytic combustion of diesel soot particulates over LaMnOs perovskite-type oxides prepared by malic acid method has been studied. In the LaMn03 catalyst, the partial substitution of alkali metal ions into A site enhanced the catalytic activity in the combustion of diesel soot particulates and the activity was shown in following order Cs>K>Na. In the LarxCs MnOj catalyst, the catalytic activity increased with an increase of X value and showed constant activity at the substitution of x>0.3... 

Several researchers have focused their attention on the application of oxide materials to lower the oxidation temperature of soot particulates. It was reported that active soot oxidation catalysts are PbO, C03O4, V2O5, M0O3, CuO, and perovskite type oxides[3]. 

Fig. 1. TG spectra of carbon particulates with Fig. 2. TPR profiles measured for various Lao.gCso MnOj catalyst heating rate=l K/min. perovskite type oxides heating rate=10 K/min,...

Fig. 2 shows the temperature as a function of irradiation time of Cu based material under microwave irradiation. CuO reached 792 K, whereas La2Cu04, CuTa20e and Cu-MOR gave only 325, 299 and 312 K, respectively. The performances of the perovskite type oxides were not very significant compared to the expectation from the paper reported by Will et al. [5]. This is probably because we used a single mode microwave oven whereas Will et al. employed multi-mode one. The multi-mode microwave oven is sometimes not very sensitive to sample s physical properties, such as electronic conductivity, crystal sizes. From the results by electric fixmace heating in Fig. 1, at least 400 K is necessary for NH3 removal. So, CuO was employed in the further experiments although other materials still reserve the possibility as active catalysts when we employ a multi-mode microwave oven. 

The Incentive to modify our existing continuous-flow microunit to incorporate the square pulse capability was provided by our work on perovskite-type oxides as oxidation-reduction catalysts. In earlier work, it had been inferred that oxygen vacancies in the perovskite structure played an important role in catalytic activity (3). Pursuing this idea with perovskites of the type Lai-xSrxFeg 51 10 503, our experiments were hampered by hysteresis effects which we assumed to be due to the response of the catalyst s oxygen stoichiometry to the reaction conditions. 

The activities of the perovskite-type oxides are strongly dependent on pretreatment in reducing or oxidizing atmospheres at a.600°C. This was found for other perovskite catalysts as well (1). Reducing pretreatments lead to more active catalysts (Figures 5 and 6). The reason for this is not known, but better binding of CO to the reduced surface is a possible explanation. 

Perovskites, 27 358 band structure, 38 131-132 crystal structure, 38 123-125 Perovskite-type oxides see also specific lanthanum-based catalysts actinide storage in radioactive waste, 36 315-316... 

Nishihata et al. (2002) reported the re-dispersion of Pd in a Perovskite-type oxide. They investigated the oxidation state and the local structure of Pd by using X-ray absorption analysis. Pd occupies the -site in La2PdCo06 in the oxidized sample. For the reduced catalyst, the XAD and XANES measurements suggested the segregation of metallic Pd from the perovskite crystal. They imply that Pd also moves back and forth between the -site in the perovskite structure and sites within the lattice of Pd metal clusters dispersed on perovskite surface when the catalyst is exposed to fluctuations in the redox characteristics of the emission exhaust. 

The extensive variety of properties that these compounds show is derived from the fact that around 90% of the metallic natural elements of the periodic table are known to be stable in a perovskite-type oxide structure [74], Besides, the possibility of synthesizing multicomponent perovskites by partial substitution of cations in positions A and B gives rise to substituted compounds with a formula A, A B,. B 03 ft. The resulting materials can be catalysts, insulators, semiconductors, superconductors, or ionic conductors. 

Perovskite-type oxides are well known oxidation catalysts in the gas phase [259]. In 1970, Meadowcroft suggested that LaCo03 doped with strontium was a less expensive alternative to platinum for air cathodes in alk-... 

The various processes for the catalytic reaction are similar. The factor that makes the difference is the choice of catalyst, which in turn affects the temperature regime needed to trigger the decomposition of nitrous oxide. In the literature, numerous works illustrate the several classes of catalysts appropriate for this reaction [9a, k] noble metals (Pt, Au), pure or mixed metal oxides (spinels, perovskite-types, oxides from hydrotalcites), supported systems (metal or metal oxides on alumina, silica, zirconia) and zeolites. 

In recent years, much attention has been focused on hydrocarbons total oxidation over mixed oxides. It was reported that perovskite type oxides remarkably oxidise carbon monoxide, light alkanes and also methane at low temperatures [1]. However, the major obstacles to the successful application of these materials in a large scale are both then-low resistance to sulphur poisoning and also their scarce BET surface area which is often linked to the catalytic activity. For this, development of more active catalysts has become a challenge to be overcome. Many attempts have been made to develop new preparation methods to improve... 

Voorhoeve et al. (1972) were the first to report the high catalytic activity of perovskite-type oxides for heterogeneous oxidation, triggering many studies thereafter, which used these materials as catalysts for hydrocarbon combustion. 

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