Aerobic oxidation of methane

The aerobic oxidation of methane in water catalyzed by [Pt(Mebipym)Cl2] [PV2Mo1004o]5 (Mebipym = N-methy-2,2 -bipyrimidine) complex supported on Si02 was reported [149]. The conjugation of [PV2Mo1004o]5 to a known Pt2 + -bipyrimidine complex by electrostatic interaction could fadlitate the oxidation of the Pt2 + intermediate to a Pt4 + intermediate by 02, resulting in the catalytic aerobic oxidation of methane to methanol in water and then surprisingly further to acetaldehyde via a carbon-carbon coupling reaction. 

The aerobic oxidation of methane is carried out by bacteria called methanotrophs (1). These bacteria grow on methane as their sole carbon and energy source, oxidizing a portion of the methane to C02 and fixing a portion into cell material. They are obligate aerobes because the methane oxidation reaction requires molecular oxygen. 

Aerobic oxidation of methane catalyzed by [R(Mebipym)Cl2] [H4PV2Moio04o] /Si02... 

The supramolecular environment can not only protect an active species but also stabilize it through local constraints. Cu-ZSM-5, a Cu-loaded zeolite where Cu ions are incorporated into the walls, was proposed to generate a mono-(/z-oxo)-dicopper core upon activation at 723 K under an O2 flow, as evidenced by UV experiments. Aerobic oxidation of methane was carried out at 448 K and CH3OH was detected as the only product, trapped inside the host. The nature of the host (Al/Si and Cu/Al ratios)... 

Scheme 9.12 Consensus catalytic scheme for the oxidation of methane and the catalyst and reactions observed in the aerobic oxidation of methane in water.

Figure 4.15. Block diagram for formation and transport of methane in waterlogged country. Notation FlCHi is the methane flux across the atmosphere/water body interface F2CHi is the oxidation of methane in aerobic zones FCH is the intensity of the methane source M is methane concentration.

Direct oxidation of the lesser chlorinated ethenes, ethanes, polychlorinated benzenes, and chlorobenzene has been reported. Wiedemeier et al. [25] summarize a number of studies that report direct aerobic oxidation of vinyl chloride (VC), 1,2-dichloroethane, the three dichlorobenzene isomers, 1,2,4-trichlorobenzene, and 1,2,4,5-tetrachlorobenzene. Bradley [33] reports that DCE has served as a primary substrate for energy production with oxygen as the electron acceptor, though use of DCE as a sole carbon source has not been demonstrated. Rittmann and McCarty [29] also report that the two least chlorinated methanes (dichloromethane and chloromethane) as well as chloroethane can be directly oxidized under aerobic conditions. Direct oxidation of the chlorinated compounds is typically modeled using either first-order or Monod kinetics [29,31]. 

Aerobic oxidation of alkanes requires dioxygen, hence it was originated only after plant photosynthesis thereby producing most part of the dioxygen on earth. Meanwhile methane is produced in anaerobic methanogenesis, therefore apparently this biological process existed before when life on earth was... 

There are only two important sinks that serve to destroy methane. The first is the oxidation of methane by aerobic bacteria in soils whereas the second and the most important sink is reaction (oxidation) with hydroxyl radicals in the atmosphere. Biological oxidation of methane in soils is responsible for 6-10% of the global source strength. Oxidation dne to the reaction of methane with hydroxyl radicals in the atmosphere, however, accounts for the remaining 90% (Cicerone and Oremland, 1988). An estimated 500 Tg year is removed from the atmosphere each year over 95% of the annual emission is removed through these two primary sinks (Khalil et al., 1992). 

The same authors developed an interesting system for aerobic oxidation of propene using the palladium(ii) catalysts with chelating bis(NHC) ligands and NaVOs as co-catalyst. The palladium(ii) catalyst was responsible for C-H functionalization, while the vanadium co-catalyst mediated the O2 activation. Both catalytic cycles were connected by a bromide-bromine redox pair, which mediated the C-H activation by oxygen. Unfortunately, a similar catalytic system for the oxidation of methane was extremely slow, probably due to decomposition of the catalyst. 

Decomposition of organic matter under aerobic conditions results in the production of simple mineral compounds, i.e. carbon dioxide and water, but also humic-like substances (Ritzkowski et al. 2006). However, due to the heterogeneity of waste structure, the oxygen does not reach in the same amount all the places in landfill. Its concentration is determined by the waste moisture and porosity. As a result of oxygen diffusion impairment methanogen-esis, denitrification, and sulphate reduction occur. Moreover, there are the processes such as the oxidation of an organic matter, the nitrification or the oxidation of methane that also take place there. Therefore, in the gas generated in aerated landfills CH, NH and H S are present beside of the CO, CO or water vapor. 

Some of these preventive and protective measures are described in Mitigation of Landfiii Gas Emissions. Special attention is given to the application of anaerobic, aerobic and semi-aerobic bioreactor landfills for control of landfill gas emission. Different types of biotic systems for the oxidation of methane and trace gases, such as biocovers, biofilters, and biowindows, are also presented. 

In some cases, microorganisms can transform a contaminant, but they are not able to use this compound as a source of energy or carbon. This biotransformation is often called co-metabolism. In co-metabolism, the transformation of the compound is an incidental reaction catalyzed by enzymes, which are involved in the normal microbial metabolism.33 A well-known example of co-metabolism is the degradation of (TCE) by methanotrophic bacteria, a group of bacteria that use methane as their source of carbon and energy. When metabolizing methane, methanotrophs produce the enzyme methane monooxygenase, which catalyzes the oxidation of TCE and other chlorinated aliphatics under aerobic conditions.34 In addition to methane, toluene and phenol have been used as primary substrates to stimulate the aerobic co-metabolism of chlorinated solvents. 

TCE is the other major contaminant at the site and is a common groundwater contaminant in aquifers throughout the United States [425]. Since TCE is a suspected carcinogen, the fate and transport of TCE in the environment and its microbial degradation have been extensively studied [25,63, 95,268,426,427]. Reductive dechlorination under anaerobic conditions and aerobic co-metabolic processes are the predominant pathways for TCE transformation. In aerobic co-metabolic processes, oxidation of TCE is catalyzed by the enzymes induced and expressed for the initial oxidation of the growth substrates [25, 63, 268, 426]. Several growth substrates such as methane, propane, butane, phenol, and toluene have been shown to induce oxygenase enzymes which co-metabolize TCE [428]. 

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