Researchers have made advances in converting methane to methanol, or other liquids, which can be more easily transported than gas. This could promote the substitution of methane -- the primary component of natural gas -- for petroleum-based fuels, according to an article in the journal Science, which was published late last month.
Methane is valued for its high-energy carbon-hydrogen bonds, which consist of a carbon atom bound to four hydrogen atoms. The gas does not react easily with other materials and so it is most often simply burned as fuel. Burning breaks all four hydrogen-carbon bonds and produces carbon dioxide and water, said Karen Goldberg, a University of Washington (UW) chemistry professor.
Converting methane into useful chemicals, including readily transported liquids, currently requires high temperatures and a lot of energy. Catalysts that turn methane into other chemicals at lower temperatures have been discovered, but they have proven to be too slow, too inefficient or too expensive for industrial applications, Goldberg said.
Binding methane to a metal catalyst is the first step required to selectively break just one of the carbon-hydrogen bonds in the process of converting the gas to methanol or another liquid. In their paper, the researchers describe the first observation of a metal complex (a compound consisting of a central metal atom connected to surrounding atoms or molecules) that binds methane in solution. This compound serves as a model for other possible methane complexes. In the complex, the methane's carbon-hydrogen bonds remained intact as they bound to a rare metal called rhodium.
The work should spur advances in developing catalysts to transform methane into methanol or other liquids, Goldberg said, although she noted that actually developing a process and being able to convert the gas into a liquid chemical at reasonable temperatures still is a ways off. "The idea is to turn methane into a liquid in which you preserve most of the carbon-hydrogen bonds so that you can still have all that energy," she said. "This gives us a clue as to what the first interaction between methane and metal must look like."
Maurice Brookhart, a University of North Carolina (UNC) at Chapel Hill chemistry professor, said carbon-hydrogen bonds are very strong and hard to break, but in methane complexes breaking the carbon-hydrogen bond becomes easier. "The next step is to use knowledge gained from this discovery to formulate other complexes and conditions that will allow us to catalytically replace one hydrogen atom on methane with other atoms and produce liquid chemicals such as methanol," Brookhart said.
The lead author of the paper is Wesley Bernskoetter of Brown University, who did the work while at UNC. Goldberg, Brookhart and Cynthia Schauer, associate chemistry professor at UNC, are co-authors. The work comes out of a National Science Foundation-funded collaboration, the UW-based Center for Enabling New Technologies Through Catalysis, which involves 13 universities and research centers in the United States and Canada, including UNC. Additional funding came from the National Institutes of Health.
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