Reduction methane oxidation

The influence of Zn-deposition on Cu(lll) surfaces on methanol synthesis by hydrogenation of CO2 shows that Zn creates sites stabilizing the formate intermediate and thus promotes the hydrogenation process [2.44]. Further publications deal with methane oxidation by various layered rock-salt-type oxides [2.45], poisoning of vana-dia in VOx/Ti02 by K2O, leading to lower reduction capability of the vanadia, because of the formation of [2.46], and interaction of SO2 with Cu, CU2O, and CuO to show the temperature-dependence of SO2 absorption or sulfide formation [2.47]. 

A few examples of chemoautolithotrophic processes have been mentioned in this chapter, namely anaerobic methane oxidation coupled to sulfate reduction and the ones listed in Table 12.2 involving manganese, iron, and nitrogen. Another example are the microbial metabolisms that rely on sulfide oxidation. Since sulfide oxidation is a source of electrons, it is a likely source of energy that could be driving denitrification, and manganese and iron reduction where organic matter is scarce. 

Biodegradation by enzymes of genetically engineered strains Biooxidation after reductive or oxidative biodechlorination Biooxidation after reductive or oxidative biodechlorination Biooxidation by cometabolization with methane or ammonium... 

The present chapter will primarily focus on oxidation reactions over supported vanadia catalysts because of the widespread applications of these interesting catalytic materials.5 6,22 24 Although this article is limited to well-defined supported vanadia catalysts, the supported vanadia catalysts are model catalyst systems that are also representative of other supported metal oxide catalysts employed in oxidation reactions (e.g., Mo, Cr, Re, etc.).25 26 The key chemical probe reaction to be employed in this chapter will be methanol oxidation to formaldehyde, but other oxidation reactions will also be discussed (methane oxidation to formaldehyde, propane oxidation to propylene, butane oxidation to maleic anhydride, CO oxidation to C02, S02 oxidation to S03 and the selective catalytic reduction of NOx with NH3 to N2 and H20). This chapter will combine the molecular structural and reactivity information of well-defined supported vanadia catalysts in order to develop the molecular structure-reactivity relationships for these oxidation catalysts. The molecular structure-reactivity relationships represent the molecular ingredients required for the molecular engineering of supported metal oxide catalysts. 

According to Lunsford, most of the observations on methane oxidation over oxide catalysts may be interpreted in terms of methyl radical chemistry.41 Most experimental data support the role of surface O- ions in the formation of methyl radicals. The latter are transformed by reductive addition to methoxide ions, which decompose to formaldehyde or react with water to form methanol. Methyl radicals may desorb to the gas phase and participate in free-radical reactions to yield non-selective oxidation products. 

Devol, A.H., Anderson, J.J., Kuivila, K., and Murray, J.W. (1984) A model for coupled sulfate reduction and methane oxidation in the sediments of Saanich Inlet. Geochim. Cosmochim. Acta 48, 993-1004. 

A search for organisms with novel metabolic and bioenergetic pathways, particularly pathways involved in carbon dioxide and carbon monoxide reduction and methane oxidation coupled with electron acceptors other than oxygen ... 

While Table 8 includes reactions for the formation of thermal NO, it does not include those for prompt NO. Mechanisms and reaction rate data for prompt NO formation and various methods for the reduction of NO have been described by Millerand Bowman (Prog. Energy Combust. 5ci., 15,287,1989). The GRIMECH reaction set (http //www.me.berkeley.edu/grijnech) is an example of a high temperature methane oxidation mechanism that includes both thermal and prompt NO production. 

Three primary mechanisms have been offered to explain anaerobic CH4 oxidation in marine sediments. The process may be carried out by a single organism that couples methanotrophy to S04 reduction. Anaerobic methane oxidation coupled to sulfate reduction is thermodynamically... 

Niewohner C., Heasen C., Kasten S., Zabel M., and Schulz H. D. (1998) Deep sulfate reduction completely mediated by anaerobic methane oxidation in sediments of the upwelling area off Namibia Geochim. Cosmochim. Acta 62, 455-464. 

Because of its abundance in anoxic aquatic environments and its importance as a greenhouse gas, methane transformation by anaerobic oxidation has been the subject of numerous studies. The rates of anaerobic methane oxidation and the environments where it has been found were reviewed by Spormann and Widdel (2000). In marine systems, sulfate reduction has been shown to be an important part of the methane oxidation process. Landhlls, however, not hydrocarbon contaminations per se, are the main source of anthropogenic methane emissions in the US and, therefore, methane degradation processes are not discussed further in this chapter (see Chapter 9.16 for a discussion of methane generation from landfills). 

To summarize, the isotopic and textural evidence collectively implies the activity in the Belingwe belt of a variety of prokaryotic processes (1) sulphate reduction and possibly photosynthetic sulphide oxidation (2) operation of rubisco both in cyanobacterial stromatolites (as expected) but also possibly in non-photosynthetic sulphur-bacterial mats (3) oxygenic photosynthesis (in stromatolites) (4) methanogenesis and methane oxidation. Most probably, other sulphur-based metabolic reactions (e.g. dissim-ilatory sulphate reduction) were also taking place. This complexity is consistent with the relative timing of the metabolic phylogeny deduced from rRNA studies (Woese 1987 Pace 1997). 

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