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The burning of fossil fuels such as coal and natural gas releases carbon into the atmosphere as CO2 while the production of methanol and other valuable fuels and chemicals requires a supply of carbon. There is currently no economical or energy efficient way to collect CO2 of the atmosphere and use it to produce carbon-based chemicals, but researchers at the Swanson School of Engineering at the University of Pittsburgh have just taken an important step in that direction.
The team worked with a class of nanomaterials called metallic-organic structures or "MOFs", which can be used to extract carbon dioxide from the atmosphere and combine it with hydrogen atoms to convert it into chemicals and in valuable fuels. Karl Johnson, Professor William Kepler Whiteford at the Swanson School's Department of Chemical and Petroleum Engineering, led the research group as principal investigator.
"Our ultimate goal is to find an MOF with low energy consumption and able to separate carbon dioxide from a gas mixture and prepare it to react with hydrogen," said the Dr. Johnson. "We found an MOF that could bend the CO2 molecules slightly, taking them to a state in which they react with hydrogen more easily. "
The Johnson Research Group published its findings in the journal of the Royal Society of Chemistry (RSC) Science and technology of catalysis. The review presented their work on its cover, illustrating the process of the carbon dioxide and hydrogen molecules entering the MOF and coming out in CH form.2O2 or formic acid – chemical precursor of methanol. For this process to occur, molecules must overcome a demanding energy threshold called a hydrogenation barrier.
Dr. Johnson explains, "The hydrogenation barrier is the energy needed to add two atoms of H to CO2which converts the molecules into formic acid. In other words, it's the energy needed to get the H atoms and the CO2 molecules together so that they can form the new compound. In our previous work, we were able to activate H2 separating two atoms of H, but we could not activate the CO2 until now. "
The key to reducing the hydrogenation barrier was to identify an MOF capable of pre-activating carbon dioxide. Pre-activation essentially consists in preparing the molecules for the chemical reaction by placing them in the correct geometry, in the right position or in the good electronic state. The MOF that they modeled in their work performs a pre-activation of CO2 placing it in a slightly curved geometry capable of accepting incoming hydrogen atoms with a lower barrier.
Another key feature of this new MOF is that it reacts selectively with hydrogen molecules on carbon dioxide, so active sites are not blocked by CO.2. "We designed an MOF whose space around binding sites is limited, so that there is not enough room to bind the CO2, but there is still plenty of room to connect H2because it's so much smaller. Our design ensures that CO2 does not bind to MOF but is free to react with H molecules already present in the frame, "says Dr. Johnson.
Dr. Johnson is thinking of developing a single material that can both capture and convert CO2 would be economically viable and reduce the net amount of CO2 in the atmosphere. "You can capture CO2 flue gases in power plants or directly from the atmosphere, "he explains. This research restricts our search for a very rare material capable of transforming a hypothetical technology into a real benefit for the world. "
The Pitt Center for Computer Research has provided computer resources.
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Material provided by University of Pittsburgh. Note: Content can be changed for style and length.
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