Methane, oxidation over perovskites

Table 4 Catalytic activity of methane oxidation over perovskite-type oxides and Pt/alumina catalysts ...

Kharton, V., Patrakeev, M., Waerenborgh, J., et al. (2005). Methane oxidation over perovskite-related ferrites Effects of oxygen nonstoichiometry, Solid State Set, 7, pp. 1344-1352. 

H., Yang, Y.L., and Jacobson, A.J. (1997) Reaction kinetics of methane oxidation over LaCri. ijeOa perovskite catalysts. 

P. Salomonsson, T. Griffin, and B. Kasemo, Oxygen desorption and oxidation-reduction kinetics with methane and carbon monoxide over perovskite type metal oxide catalysts, Appl CataL A. 704 175 (1993). 

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... 

Perovskite-type metal oxides are promising candidates as deep oxidation catalysts due to their robustness and good resistance to sulphur poisoning. Three sorts of reaction mechanism have been proposed for methane combustion over different perovskites, i.e. 

The catalytic combustion of methane over perovskite-type catalysts has been investigated by Arai and co-workers (66). Methane is the most stable alkane, and it is relatively difficult to combust by virtue of the high strength of the C—H bond that must be activated. Studies were performed using relatively high space velocities in the range 45,000-50,000 h , with a 2% methane feed in air. The catal3Ttic activity, expressed as the temperature required for 50% conversion, is shown in Table 13 for a series of unsubstituted perovskite-type oxides. 

Methane oxidation kinetics over LaCri cNi c03 (x = 0 to 1) perovskites has been studied by Stojanovic et al. [113]. The catalytic activity was found to be proportional to x. It was also observed that nickel could be reduced to the metallic form by starving the catalyst of oxygen. A redox process involving surface Ni-O-Ni species in methane oxidation has been proposed. 

H Aral, T Yamada, K Eguchi, and T Seiyama, Catalytic combustion of methane over vanous perovskite-type oxides, Appl Catal 26 265 (1986)... 

Among the cobalt containing perovskites GdCoO, SmCoO, NdCoO, PrCoO, and LaCoO, tested as catalyst precursors for the partial oxidation of methane the Gd-Co-0 system showed exceptionally better performance for synthesis gas formation (Figs. 6A-6C). At 1009 K a steady-state methane conversion of 73% with selectivities of 79 and 81% for CO and H., respectively, is observed for the catalyst Gd-Co-O. The catalysts Sm-Co-O and Nd-Co-0, of lower activity, show similar steady-state methane conversions in the temperature range studied. On the other hand, the H, and CO selectivities are much higher over Sm-Co-O. 

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... 

Methane or natural gas steam reforming performed on an industrial scale over nickel catalysts is described above. Nickel catalysts are also used in large scale productions for the partial oxidation and autothermal reforming of natural gas [216]. They contain between 7 and 80 wt.% nickel on various carriers such as a-alumina, magnesia, zirconia and spinels. Calcium aluminate, 10-13 wt.%, frequently serves as a binder and a combination of up to 7 wt.% potassium and up to 16 wt.% silica is added to suppress coke formation, which is a major issue for nickel catalysts under conditions of partial oxidation [216]. Novel formulations contain 10 wt.% nickel and 5 wt.% sulfur on an alumina carrier [217]. The reaction is usually performed at temperatures exceeding 700 °C. Perovskite catalysts based upon nickel and lanthanide allow high nickel dispersion, which reduces coke formation. In addition, the perovskite structure is temperature resistant. 

Arai, H., Yamada, T., Eguchi, K., and Seiyama, T. (1986) Catalytic combustion of methane over various perovskite-type oxides. Appl. Catal., 26, 265-276. Wakabayashi, Y., Upton, M.H., Grenier, S., Hill, J.P., Nelson, C.S., Kim, J.W., Ryan,... 

Dry reforming of methane over Ni perovskite type oxides. Catal. Today, 107, 785-791. 

Saracco et al. [26] tested perovskite catalysts LaMni Mg 03 for the deep oxidation of methane. A Rideal-Eley mechanism fitted satisfactorily the experimental kinetics for LaMn03 and Mg-doped LaMn03. However, as opposed to LaMn03, the catalytic combustion over LaMno.8Mgo.2O3 seemed to involve two different types of adsorbed oxygen species, depending on the operating temperature. 

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