Methane oxidation, catalytic

G. Veser, J. Frauhammer, Modeling steady state and ignition during catalytic methane oxidation in a monolith reactor. Chem. Eng. Sci.,... 

Very similar results were also obtained by Farrauto et al. [51] from a study of the high-temperature catalytic chemistry of supported Pd for the combustion of methane. Palladium oxide supported on alumina decomposes in two distinct steps in air at atmospheric pressure. The first step occurs between 750 and 800X and is believed to be a decomposition of Pd-O species dispersed on bulk Pd metal, designated (PdO /Pd). The second decomposition occurs between 800 and 850" C, and it behaves like crystalline palladium oxide (PdO). To form the oxide once again, metallic Pd has to be cooled down to 650°C, thus causing a hysteresis gap of 150°C. Above 500°C, catalytic methane oxidation can occur only as long as the palladium oxide phase is still present. Above 650 C, metallic Pd cannot chemisorb oxygen, and hence it is catalytically inactive toward methane oxidation. 

Two examples of low temperature, catalytic, methane oxidation by hydrogen peroxide should be included in this section. The first involves conversion to methanol using cis-[Ru(2,9-dimethyl-l,10-phenanthroline)(solvent)2](PF6)2 as the catalyst [39]. A ruthenium-oxo species has been proposed as the C-H activating species. In the second report, conversion of methane to methyl hydroperoxide is claimed [40]. The catalyst is a combination of [NBuJ V03 and pyrazine-2-carbox-ylic acid. While the mechanism is uncertain, the actual oxidant is believed to be dioxygen with HO derived from hydrogen peroxide acting as the initiator. 

Several parameters that affect catalytic methane oxidation on a natural gas vehicle were investigated with laboratory aged noble metal catalysts and a simulated vehicle exhaust. These include the air/fliel control strategy, the noble metal loading, the role of base metals and the exhaust hydrocarbon composition. The catalytic performance of several formulations was compared both slightly fuel-rich of the stoichiometric point and under extreme lean conditions. 

D. Eng, and M. Stoukides, Catalytic and Electrocatalytic Methane Oxidation with Solid Oxide Membranes, Catalysis Reviews - Science and Engineering 33, 375-412 (1991). 

This linear variation in catalytic activation energy with potential and work function is quite noteworthy and, as we will see in the next sections and in Chapters 5 and 6, is intimately linked to the corresponding linear variation of heats of chemisorption with potential and work function. More specifically we will see that the linear decrease in the activation energies of ethylene and methane oxidation is due to the concomitant linear decrease in the heat of chemisorption of oxygen with increasing catalyst potential and work function. 

O.A. Mar ina, V.A. Sobyanin, V.D. Belyaev, and V.N. Parmon, The effect of electrochemical pumping of oxygen on catalytic behaviour of metal electrodes in methane oxidation, in New Aspects of Spillover Effect in Catalysis for Development of Highly Active Catalysts, Stud. Surf. Sci. Catal. 77 (T. Inui, K. Fujimoto, T. Uchijima,... 

The catalytic partial oxidation of methane into CO and H2 according to... 

The catalytic partial oxidation of methane for the production of synthesis gas is an interesting alternative to steam reforming which is currently practiced in industry [1]. Significant research efforts have been exerted worldwide in recent years to develop a viable process based on the partial oxidation route [2-9]. This process would offer many advantages over steam reforming, namely (a) the formation of a suitable H2/CO ratio for use in the Fischer-Tropsch synthesis network, (b) the requirement of less energy input due to its exothermic nature, (c) high activity and selectivity for synthesis gas formation. 

Tonkovich, A. L. Y, Zilka, J. L., Powell, M. R., Gall, C. J., The catalytic partial oxidation of methane in a micro-channel chemical reactor, in Ehrfeld, W, Rinard, I. H., Wegeng, R. S. (Eds.), Process Miniaturization 2nd International Conference on Microreaction Technology, IMRET 2, Topical Conf. Preprints, pp. 45-53, AIChE, New Orleans (1998). 

The Pd-ZSM-5 catalysts are prepared by impregnation and by solid exchange methods on the carrier of HZSM-5 and NaZSM-5 (Si/Al = 26) with variable palladium loading and different pre-treatment gas (He and O2). N2-physisorption, DRX and CH4-TPR are the main techniques used to characterise these catalysts. Furthermore, total methane oxidation is used to test their catalytic activity. Among the preparative variables, the solid exchange method, the NaZSM-5 support and the increase of the palladium loading improve considerably the activity of the Pd-ZSM-5 catalysts in methane oxidation. 

Supported palladium oxide is the most effective catalyst used in total methane oxidation and in catalytic oxidation of VOCs [1-5]. However, the activity of the conventional catalysts is not sufficient [5-6]. Recently, the Pd-zeolite catalysts have attracted considerable attention due to their high and stable CH4 conversion efficiency [4-8]. In this work, the effect of the preparation method, the nature of the charge-balancing cations, the palladium loading and the pre-treatment gas nature on the texture, structure and catalytic activity of the Pd-ZSM-5 solids are investigated. 

Voutetakis, S. et al., Catalytic partial oxidation of methane in a spouted bed reactor, in Natural Gas Conversion V, Studies in Surface Science and Catalysis, vol. 119, Parmaliana, A. et al., Eds., Elsevier, Amsterdam, 807 1998. 

The other two main processes for conversion of methane into synthesis gas are partial oxidation and CO2 reforming. In the 1940s, Prettre et al. (3) first reported the formation of synthesis gas by the catalytic partial oxidation of CH4... 

They used a Ni-containing catalyst. In contrast to steam reforming of methane, methane partial oxidation is exothermic. However, the partial oxidation requires pure oxygen, which is produced in expensive air separation units that are responsible for up to 40% of the cost of a synthesis gas plant (2) (in contrast, the steam reforming process does not require pure oxygen). Therefore, the catalytic partial oxidation of methane did not attract much interest for nearly half a century, and steam reforming of methane remained the main commercial process for synthesis gas manufacture. 

The catalytic activities of some perovskites for methane oxidation and steam reforming have also been studied, and it appears that the activity of some materials can be reasonably attractive. Con-... 

Numerous studies have been published on catalyst material directly related to rich catalytic combustion for GTapplications [73]. However, most data are available on the catalytic partial oxidation of methane and light paraffins, which has been widely investigated as a novel route to H2 production for chemical and, mainly, energy-related applications (e.g. fuel cells). Two main types of catalysts have been studied and are reviewed below supported nickel, cobalt and iron catalysts and supported noble metal catalysts. 

Co and Fe catalysts have also been studied for the partial oxidation of methane to synthesis gas. Their potential relies on the fact that Co and Fe have higher melting and vaporizing points than Ni. Lower performances were mostly observed, however, which is probably related to the higher activity of CoO and FC2O3 for the complete oxidation of methane [121, 132, 133]. The recognized order of reactivity for partial oxidation is in fact Ni Co > Fe. However, it was observed that the performance of Co improves when a promoter is added. An extensive study of the catalytic partial oxidation of methane over CO/AI2O3 catalysts with different metals (0.1 wt% of Ni, Pt,... 

B. (1998) A study of the structural and catalytic effect of sulphation on iron oxide catalysts prepared from goefhite and ferrihydrite precursors for methane oxidation. Catalysis Letters 53 7—13... 

Pfefferle and Lyubovsky executed types of measurements that yielded critical information between active Pd phases for catalytic combustion using pure ot-alumina plates with zero porosity as a support for the catalyst. This procedure uniformly covers the plate with metal particles on the top surface where they are easily available for the reaction gases and optical analysis. This type of experimental procedure has shown that in high-temperature methane oxidation the reduced form of the supported palladium catalyst is more active than the oxidized form. The temperature at which the PdO Pd... 

Catalytic Activity. The world-wide interest focused in the catalytic partial oxidation of methane to formaldehyde has led to a great variety of conflicting results (9), The main reason of such discrepancies lies in the lack of a generally valid rule for evaluating and comparing the proposed catalytic systems. In effect, this reaction involves a very complex pathway since the desired partial oxidation product, HCHO, exhibits a limited thermal stability at T>4(X)°C and can be oxidized to more easily than CH itself. Hence, a suitable reactor device and appropriate operating conditions result to be of fundamental importance in order to attain reliable data unaffected by experimental artefacts. 

The catalytic homogeneous oxidation at low temperatures is therefore economically interesting, but also very difficult to achieve due to the high stability of CH-bonds. Partial oxidation is particularly hard in alkanes as classical oxidation procedures tend to over oxidize them. In the case of methane this would result in the formation of CH2O, CO and CO2. Low valent transition metals, however, are capable of activating the CH bond and rendering that problem less important as the difference in reactivity between the CH bond in methane and methanol is not that big. 

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