Total Oxidation of Methane

Concerning the reaction pathway, two routes have been proposed the sequence of total oxidation of methane, followed by reforming of the unconverted methane with CO2 and H2O (designated as indirect scheme), and the direct partial oxidation of methane to synthesis gas without the experience of CO2 and H2O as reaction intermediates. The results obtained by Schmidt and his co-workers [4, 5] indicate that the direct reaction scheme may be followed in a monolith reactor when an extremely short contact time is employed at temperatures in the neighborhood of 1000°C. However, the majority of previous studies over numerous types of catalysts show that the partial oxidation of methane follows the indirect reaction scheme, which is supported by the observation that a sharp temperature spike occurs near the entrance of the catalyst bed, and that essentially zero CO and H2 selectivity is obtained at low methane conversions (<25%) where oxygen is not fully consumed [2, 3]. A major problem encountered... 

Zavyalova U., Scholz R, and Ondruschka B. 2007. Influence of cobalt precursor and fuels on the performance of combustion-synthesised C03O4/Y-AI2O3 catalysts for total oxidation of methane. Appl. Catal. A Gen. 323 226-33. 

Figure 4.3.7 Combined X-ray absorption spectroscopy (XAS), XRD, and Raman studies over flame-made 10 wt% Pd/Zr02 during the total oxidation of methane XAS and XRD were performed consecutively during the first heat up. The Raman spectra during the first heat up cycle did not show any PdO present therefore, spectra from the second heat up are shown (for details, cf. [35, 39]).

Grunwaldt JD, van Yegten N, Baiker A. Insight into the structure of supported palladium catalysts during the total oxidation of methane. Chem Commun. 2007 4635. 

Mn0i/Ce02-Zr02 and Mn0i/W03-Ti02 catalysts for the total oxidation of methane and chlorinated hydrocarbons... 

The aim of the present work was to examine supported MnOx catalysts and to clarify the influence of the support (Ti02, WOs-TiOi, Zr02, Ce02 -Zr02) on the textural, structural and catalytic properties for the total oxidation of methane and chloromethane, considering catalyst deactivation and formation of by-products. 

A continuous fixed bed reactor coupled on-line with a GC (FID/TCD) was used for the catalytic experiments. The amoimt of catalyst (particle size diameter 0.1 - 0.3 mm) loaded was 0.6 g. The catalytic behaviour of the catalysts was investigated in the total oxidation of methane and chloromethane (1 vol.% in air, feed stream 5 1/h) considering by-product formation. 

The catalytic activity was investigated for the total oxidation of methane and chloromethane as testing reactions. Selected results are presented in Fig. 2 and Fig. 3 Compared with the impregnated MnOx/ZrOz catalysts the catalytic activity of the precipitated catalysts for the methane conversion is higher [15]. The best results were obtained for MnOx loadings between 20 and 40 mol% (Fig. 2). With respect to the structural investigations it is suggested that the amount of X-ray amorphous (dispersed) MnOx species on the ZrOz surface is responsible for the catalytic activity. Moreover, with... 

It is known that supported palladium catalysts are the most active for the total oxidation of methane [3], and there are many studies focusing on the alumina supported ones [4 and references cited therein] However, alumina is not stable at the temperatures commonly used for methane oxidation. To avoid this problem, other authors [5] have suggested the use of zirconia-based supports, which are considered as more thermally stable. In this way, these supports were found to present very different properties, depending on the synthesis method and the presence of additives. 

The combination of reactions (2) and (5) may be considered as a scheme for direct methane oxidation to synthesis gas (CO -f H2). Similar reactions may determine the high efficiency of mixed catalysts containing Ni and rare-earth oxides for the partial oxidation of methane to synthesis gas [9]. This mechanism does not require a preliminary total oxidation of methane followed by its reforming with CO2 and/or water which was considered as the main route for synthesis gas formation [10,11]... 

Regarding the catalytic essays, the total oxidation of methane has been studied. The light-off temperatures associated to 50% conversion of methane on the C-LS, CT-80/20-LS and T-LS were found to be 778 K, 667 K and 692 K, respectively. This result, also in agreement with those reported above, gives us a further indication of the synergistic improvement of performance achieved in the mixed oxide with reference to that exhibited by the ceria and terbia mixed oxides. 

Interesting results were reported by Choudhary et al. (1996a) concerning the simultaneous partial and total oxidation of methane (reactions 1 and 2), the gas shift reaction (3) and reforming of methane with CO2 and steam (reactions 4 and 5) over LaNiCV. 

The presence of alkali on the surface of mixed oxides, added as a promoter or fixed into the solid structure as in layered perovskites, significantly improved the C2 yield, suggesting that these elements influence the oxygen species responsible for the formation of methyl radicals and/or limit the concentration of those oxygen sites associated with the total oxidation of methane. 

A Type-I membrane containing Ce (13%) on the surface was tested at 1023 K. The results showed it to be a good catalyst for the total oxidation of methane. On the other hand, the type-II membrane, in which the support was calcia-stabilized zirconia (CSZ) and magnesia-stabilized zirconia (MSZ) showed lower activity than yttria-stabilized zirconia (YSZ). The activation energy of the last membrane (non porous) for the formation... 

Palladium-based catalysts are the most active materials for the total oxidation of methane in the presence of excess oxygen. The structure and chemical identity of the species present on the surface of these materials have a decisive influence on their specific activity and time-dependent behavior. Since the structure and composition of these species strongly depend on preparation, pretreatment, thermal history, and reaction conditions, a very broad range of specific activities... 

Ignition of CO- and H2-rich fuels, such as gasified biomass, is controlled by the ignition of CO, reported by Zwinkels et and Johansson et al. CO adsorbs strongly on some catalyst systems and retards adsorption of other fuel species and oxygen and hence ignition at low temperatures. Moreover, steam has been reported to inhibit the rate for total oxidation of methane. These results are summarized in a recent PhD Thesis by van Giezen. ... 

Among the different species that natural gas can contain, sulfur compounds can have a dramatic effect on the catalytic activity. Pd is known to be extremely sensitive to even very small amounts of sulfur. Nevertheless, the deactivation rate in presence of sulfur species in the feed can be reduced when the metal particles are impregnated onto a sulfating support [10]. In that case, the support acts as a trap for the sulfur species. The sulfates are preferably formed on the support material and the palladium particles are then protected. The formation of Pd sulfate is reported to be responsible for the loss of catalytic activity in total oxidation of methane [15], the active species being PdO. 

Marceau, E., Lauron-Pemot, H. Che, M. Influence of the metalhc precursor and of the catalytic reaction on the activity and evolution of Pt(Cl)/[delta]-A1203 catalysts in the total oxidation of methane. Journal of Catalysis 197, 394-405 (2001). 

Roth, D., Gelin, R, Primet, M. Tena, E. Catalytic behaviour of Cl-free and Cl-containing Pd/A1203 catalysts in the total oxidation of methane at low temperature. Applied Catalysis A General 203, 37 5 (2000). 

Dynamic study of methane interaction with active sites involved in the total oxidation of methane over Pd/AlaOa catalyst. 

The supported palladium catalyst known to be the most active for total methane oxidation was the subject of considerable amount of research [1-9]. However, no agreement about the mechanism reaction was observed in the literature [1-8]. The Langmulr-Hinshelwood [1-4], the Eley-Rideal [5-7], and the Mars-Van Krevelen [8], mechanisms were proposed for the total oxidation of methane on the supported palladium catalysts. This diversity is explained by the variation of the active surface in each case. Indeed, according to Burch et al.[9], the active sites can be modified by the pre-treatment conditions, by the particle size, by the support nature and by the presence of some poisons such as chlorides. Others difficulties result from the fact that it is not confirmed if the active site is a partial or a total oxidized palladium particle. In addition, little is known about the reactive oxygen form. Indeed, it is not yet established if the reactive oxygen is a chemisorbed molecular or ionic form or a lattice oxygen ion. The aim of this paper is to identify the palladium oxidation state under catalytic stream, to study the reactive form of oxygen and to propose a mechanism of the reaction. 

Catalytic combustion of VOC-s is an important technique in environmental pollution control. Total oxidation of methane is a frequently applied test reaction in combustion catalyst development research [Ferri and Fomi 1998, Saiacco et al, 1999] since among VOCs this compound is one of the most difficult to bum off. However, the reaction mechanism is not completely explored yet. 

In the preparation of syngas from methane, there is always some total oxidation of methane to CO2 and H2O as well as coke formation. Coke formation can be reduced by improving the catalytic selectivity, while CO2 and H2O can be reused in reforming reactions ... 

Fig. 3.14 Selectivity toward total oxidation of methane at 800°C. The black solid line is LSCM with 75 mol% Cr and 25 mol% Mn (LSCM7525), dashed line is LSCM5050, gray solid line is LSCM2575 and dotted line is LSM (Reprinted from [20] with permission from Elsevier)...

Figure 2.26 shows distributions of concentrations, residence time, and temperature for configuration A for probe = 5 mm in the same yz plane as in Fig. 2.25. The concentrations of methane (A) and oxygen (B) decrease relatively fast due to total oxidation of methane, which forms water (C) with a maximum at ca. 2 mm. Afterward, the water is consumed by endothermic steam reforming, which yields hydrogen (D) and carbon monoxide (not shown). The comparison of the concentrations in the different channels shows that the entire process takes place earlier (in terms of the z position) in the channel with the probe than in a channel without a probe. The reference to the real time can be seen in the plot of the residence time (E). As the velocity in channel with probe is smaller than that in the reference channel, the residence time increases faster in the -direction. Therefore, at the same position, the reaction progress in the channel with probe is advanced further than in the reference channel. The entire process is dominated by the given wall temperature (F), as the velocity is relatively small. Except for the first millimeter, all quantities are mainly homogeneous in the cross-sectional...

Popescu, L, Wu, Y., Granger, P., and Marcu, I.-C. (2014) An in situ electrical conductivity study of LaCoFe perovskite-based catalysts in correlation with the total oxidation of methane. Appl. Catal. A ... 

Stephan, K Flackenberger, M., Kiefiling, D and Wendt G. (2004) Total oxidation of methane and chlorinated hydrocarbons on zirconia supported Ai Sr Mn03 catalysts. Chem. Eng. Technol, 27 (6), 687-693. 

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