Complete Oxidation of Methane

3 SiC-Supported M0O3-Carbon-Modified Catalyst for the //-Heptane Isomerization 

Isomerization of linear saturated hydrocarbons into their branched isomers presents an alternative for refiners to increase the octane number 

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By far the majority of the million or so known compounds of carbon also contain hydrogen and oxygen. There are several important types of oxygen-containing organic compounds and they can be studied as an oxidation series. For instance, the compound methanol, CH3OH, is very closely related to methane, as their structural formulas show. Methanol can be regarded as the first step in the complete oxidation of methane to carbon dioxide and water. 

Using a temperature-programmed surface reaction (TPSR) technique, Li et al. (154) showed that this complete oxidation of methane took place on the NiO catalyst during the CHfOi reaction. Weng et al. (145) used in situ microprobe Raman and in situ time-resolved IR spectroscopies to obtain a relationship between the state of the catalyst and the reaction mechanism. These authors showed that RuC>2 in the Ru/SiC>2 catalyst formed easily at 873 K in the presence of a CH4/02/Ar (2/1/45, molar) mixture and that the dominant pathway to synthesis gas was by the sequence of total oxidation of CH4 followed by reforming of the unconverted CH4 by C02 and H20. Thus, these results indicate that the oxidation of methane takes place principally by the combustion mechanism on the oxidized form of this catalyst. 

Application to Methane Oxidation. This selection of an appropriate initial model can be accomplished as shown here for the complete oxidation of methane. A general representation of the surface reaction model is (K12)... 

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,... 

P. Gelin and M. Primet, Complete oxidation of methane at low temperature over noble metal based catalysts, a review, Appl. Catal. B 39, 1-37 (2002). 

F.H. Ribeiro, M. Chow, and R.A. Dalla Betta, Kinetics of the complete oxidation of methane over supported palladium catalysts, J, CataL 146 531 (1994). 

Balance the oxygens. This involves calculation of the number of oxygen molecules consumed during the complete oxidation of methane ... 

We have previously shown that Ir-loaded TiOz exhibited excellent catalytic activity without carbon deposition in a prolonged run [3]. The reaction was proposed to proceed through a two-step process, that is complete oxidation of methane to give CO2 and HzO, followed by reforming reactions. At a lower temperature of 600 C, Ni-AlzOz catalyst is not active. The use of oxidized diamond-supported catalyst was examined under oxidative conditions. Diamond is believed to be inert to chemical reactions. However, in the presence of oxygen diamond can be oxidized to carbon dioxide. If the oxidized diamond support could be utilized under oxidative conditions, application of diamond support could be expanded to many catalytic reactions. 

Complete oxidation of methane to carbon dioxide and water occurs when it is burned in air and controlled combustion is an extremely important source of thermal energy. Methane and O2 also form extremely dangerous mixtures in the gas phase and explosions are easily detonated. Explosions occur under oxygen-deficient conditions and CO is an important and toxic product. 

Fig. 8.7 Schematic of AOM aggregate with a syntrophic metaholism among two members that only in combination can catalyze the complete oxidization of methane with sulfate. A transfer of or acetate (CHjCOO ) from methanotrophic archaea to sulfate reducing bacteria has been proposed as an intermediate in the net process. Such an interspecies transfer of hydrogen or organic carbon is still hypothetical and has not been directly demonstrated.

The effect of 25 ppm SO2 with respect to the complete oxidation of methane over supported palladium catalysts has been examined. Pd nitrate was impregnated onto alumina, Ba-modified alumina and La-modified alumina by incipient wetness impregnation. The calculated metal loading was 2.5 wt%. Two different sets of catalysts have been prepared one calcined at 500 C and the other at 1000 C. The main purpose of these two calcinations temperatures was to obtain different metal particle sizes. The results show that the combustion activity is strongly affected by the nature of the support when large particles are present. On the other hand, the small Pd particles exhibit similar behavior regardless of the nature of the support. When SO2 is added to the gas stream, a strong deactivation is observed and the presence of additive to stabilize the support increases the loss of activity of the supported Pd particles. 

Methane is the most difficult hydrocarbon to oxidize since it contains no C-C bond, but only C-H bonds, which are more difficult to break [4]. Palladium is reported to be the most active species in catalytic combustion of methane, when operating under oxidizing atmosphere [5]. Several studies have focused on complete oxidation of methane over palladium catalysts supported on alumina [6-8]. The catalytic combustion of methane over supported palladium catalysts is reported to be stmcture sensitive the activity of the catalyst is directly influenced by the size of the metallic particles [9]. 

The purpose of the present paper is to investigate the behavior of high temperature stable support in complete oxidation of methane, when sulfur species are present in the feed. Various characterization methods have been employed here in order to give a general picture of the deactivation of supported Pd catalysts in catalytic combustion of methane. This work will examine the reactivity of supported Pd catalysts, when the metal particles are dispersed over a thermally stable material, containing rare earth elements. Moreover, we will focus on the behavior of the catalysts when sulfur species are added to the feed, as sulfur can be present in significant amounts in natural gas. 

The materials containing La or Ba exhibit high resistance to sintering and maintain a large surface area after calcination. Moreover, the crystal phase of alumina remains unchanged. Nevertheless, Ba and La, which have a strong effect on the thermal stability of alumina material, negatively affect the catalytic properties of supported Pd catalysts in complete oxidation of methane. The conversion of methane over supported Pd catalyst is lower when the support is modified by addition of rare-earth species. 

Methane is mixed with air at 20% excess over the stoichiometric requirement and undergoes combustion in a burner operating at 2 bar. The inlet gases are at 4 °C and the effluent stream is at 1000 °C. Determine the amount of heat assuming complete oxidation of methane to carbon dioxide and water. For simplicity, assume the heat capacities of the species to be constant and equal to the values given below (in J/mol) ... 

Au particles supported on reducible oxides such as titania or ceria are also efficient catalysts for the water-gas shift, the destruction of sulfur dioxide (DeSOx processes), the complete oxidation of methane, the selective or partial oxidation of propene, the hydrogenation of CO and olefins, and the reduction of NO with hydrocarbons. Depending on the conditions, Au/TiOs... 

The oxidation of alkanes by O2 to give carbon dioxide and water is by far their most economically important reaction. Oxidation of saturated hydrocarbons is the basis for their use as energy sources for heat [natural gas, liquefied petroleum gas (LPG), and fuel oil] and power (gasoline, diesel fuel, and aviation fuel). Following are balanced equations for the complete oxidation of methane (the major component of natural gas) and propane (the major component of LPG). 

Jimaiez-Braja C, Dorado F, Lucas-Consuegra A, Garcni-Vargas JM, Valverde JL (2009) Complete oxidation of methane on PdA SZ and Pd/Ce02A SZ by electroehemical promotion. Catal Today 146 326-329... 

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