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Methane and carbon dioxide conversion to hydrocarbons

The direct conversion of methane (i.e. natural gas) to higher hydrocarbons and derived products offers a viable alternative to Fischer-Tropsch chemistry. Until recently, the utilization of methane as a chemical building block was limited to free radical reactions (combustion, nitration, chlorination, etc.). Various stoichiometric organometallic insertion reactions were also discovered, but their use is so far not practical. Superacid catalysts permit oxidative condensation of methane to higher hydrocarbons, as well as the selective electrophilic conversion of methane to its monosubstituted derivatives such as methyl halides and methyl alcohol. Monosubstituted methanes can be further condensed to ethylene, propylene and derived hydrocarbons over zeolites or bifunctional acidic-basic catalysts, giving access to the whole
range of hydrocarbons essential to our everyday life. Mechanistic aspects of the methane conversion chemistry, particularly the role of pentacoordinate CH5+-type carbocationic intermediates, are also studied.

When hydrocarbons are burned they form carbon dioxide and water. They are thus non-renewable on the human time scale. Excessive burning of fossil fuels leads to increased atmospheric levels of carbon dioxide, which has been linked to global warming and climatic changes. In addition to trying to keep carbon dioxide levels down through regulations, new solutions are needed. An innovative new approach pursued by the Institute is directed at reversing the process by producing hydrocarbons from carbon dioxide and water via methyl alcohol. Some of the underlying chemistry to convert carbon dioxide using hydrogen gas (obtained by electrolytically splitting water) is already
known. Metal or superacid catalyzed reduction has made signifi cant progress to bring about the feasibility of such approach. Electricity needed for generating hydrogen is, however, costly. As we still cannot store electricity effi ciently, power plants in their off-peak periods could produce hydrogen as a means of storing electricity. It then can be used to recycle CO2 (from smokestack emissions or the atmosphere) into methyl alcohol and derived fuels. The carbon dioxide recycling technology now under development at the Institute will not only produce useful fuels, but at the same time would help mitigate global warming.

Methyl alcohol and derived fuels can also be used to produce electricity in a new generation of direct oxidation liquid feed fuel cell developed jointly with JPL-Caltech. When operating the fuel cell in its reversed mode, carbon dioxide and water can be electro-catalytically reduced to methyl alcohol. Alternatively, chemistry including that developed at the Institute allows con-
version of methyl alcohol into simple olefi ns (ethylene and propylene), and through them into gasoline, aromatics or practically any other hydrocarbon product we presently derive from oil.

(c) 2014 Loker Hydrocarbon Research Institute, USC Dana and David Dornsife College of Letters, Arts and Sciences