Concept illustration of chemically converting CO2 into fuels like methanol.
A huge part of our fight against climate change is trying to drastically reduce the greenhouse gases that we emit. There are seven types of greenhouse gases, but the one that is most important is carbon dioxide, purely because of the amount of it that is found in the atmosphere. Carbon dioxide (CO2) traps energy near the surface of the earth, which heats both the surface and the lower atmosphere. It also dissolves in the ocean, creating compounds that lead to the ocean’s acidification. Concentrations of CO2 in the atmosphere also tend to make the effects climate change worse. This makes reducing the amount of CO2 that we emit key to slowing and stopping rising global temperatures.
Currently, the way that CO2 is dealt with is by carbon capture and storage (CCS). The gas is captured before it can be released into the atmosphere. It is then transported before being stored deep underground, usually in saline aquifers or depleted oil and gas reservoirs. This is a lot of work, for no tangible result. What if it was possible to turn that CO2 into something that we could use to benefit us?
University of Michigan researchers have found a way to do just that by transforming CO2 into the renewable fuel, methanol. The U-M scientists accomplished this by developing a catalyst material known as cobalt phthalocyanine. The new technique has two steps - the first converting carbon dioxide (C02) into carbon monoxide (CO) and the second converting the CO into methanol, which can then be used as fuel. It is not the first time that CO2 has been transformed into methanol, but doing it on a large scale through electrochemical processes has proven challenging in the past.
The Cobalt phthalocyanine catalyst acts as a molecular hook for CO2 or CO molecules. The arrangement of the molecules around the cobalt metal determines how strongly each gas molecule binds. However, cobalt phthalocyanine tends to bind more strongly to CO2 molecules than to CO molecules. This leads to the CO created through the first step being displaced by another CO2 molecule before the conversion to methanol happens. The researchers used computational modelling to calculate that cobalt phthalocyanine binds CO2 over three times more tightly than it binds carbon monoxide. The theoretical result was verified through experiments measuring reaction rates when varying the amounts of CO2 and CO. The difference in binding affinity is due to how the catalyst’s electrons interact with the CO2 and CO molecules. To solve this issue, the researchers suggest redesigning the catalyst to strengthen how it interacts with CO and lessen how strongly it binds to CO2. If that drawback can be resolved, CO2 could then be transformed into methanol on a large scale.
The research was published in the journal ACS Catalysis. Co-authors of the paper include U-M’s Kevin Rivera-Cruz, Libo Yao, Paul Zimmerman, Nirala Singh and Charles McCrory.
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