Another interesting biotechnological approach is the methanation of CO2 by methanogens, a class of bacteria known to operate under anaerobic conditions (Aresta et al., 1998). Such a reaction can be carried out in vitro and can also occur electrochem-ically when cell membranes are supported over electrodes (Graetzel et al., 1987). However, such artificial conversion of CO2 into methane, though scientifically interesting, has no practical application currently.
in terms of energy savings and associated greenhouse gas (GHG) emissions, as a result of both hydrocarbon oxidation and hydrocarbon valorization. CO2 is conveniently used, for example, as a dehydrogenating agent in the conversion of C6H5CH2CH3 into styrene, C6H5CH = CH2, using TiO2, ZrO2 or TiO2-ZrO2 (Eq. 7.7) (Park and Yoo, 2004):
One of the most interesting aspects of this reaction is that CO could be converted back into CO2 using an active water-gas shift reaction (WGSR) catalyst (Eq. 7.8) so that the resulting reaction would be an effective dehydrogenation of the starting hydrocarbon (Eq. 7.9) promoted by CO2. The combination of oxidation catalysts with systems that may promote the WGSR would represent a real breakthrough in this area.
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