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Carbon dioxide (COâ‚‚) emissions are a major contributor to the climate crisis, and while the world works to reduce emissions, chemists and engineers are also working on how to capture and utilize the carbon dioxide already being emitted.

Once dismissed as impractical, researchers are developing methods to convert COâ‚‚ into a wide range of valuable products, such as consumer goods, industrial materials or chemicals. This progress is exemplified by "The COâ‚‚ Tree," which showcases the wide array of products achievable through COâ‚‚ utilization using a tree metaphor.

Hanno Erythropel, a research scientist at the Yale Center for Green Chemistry and Green Engineering at the Yale School of the Environment, is part of an international team that the article "The COâ‚‚ Tree: The Potential for Carbon Dioxide Utilization Pathways" in ACS Sustainable Chemistry & Engineering. He recently spoke with YSE News about how chemical COâ‚‚ conversion can help mitigate the climate crisis and also why it is not a silver bullet.

How does chemically converting COâ‚‚ into products work?

Chemically speaking, COâ‚‚ is a molecule like any other, and chemists convert molecules to create the materials needed for our modern society. What makes COâ‚‚ special is that it is usually the end-product of combustion and related processes, and it is considered "low energy" because to convert it back into useful materials, one needs energy and usually hydrogen to remove oxygen atoms from it.

Nevertheless, that is exactly what chemists strive for: We try to design effective ways to convert one molecule into another. When looking at the CO₂ Tree we created for the manuscript, we organized the fruits—the materials already obtainable from CO₂ today—from most reduced (all oxygen removed) such as in fuels or graphite on the left, to the most oxidized (least oxygen removed) such as in baking powder, sodium bicarbonate, on the right.

Can converting COâ‚‚ into products help us meet our climate goals?

We know that we need to reduce our COâ‚‚ output stemming from fossil resources, but the COâ‚‚ in the atmosphere can also serve as a resource, especially because we need to find and use alternative carbon sources to the currently used fossil ones. If chemists want to do their part in addressing climate change, this is a good way to say, "well, how can we convert COâ‚‚ to something useful?"

Making the materials and chemicals for our society out of COâ‚‚, rather than fossil resources, is an inherently circular approach: Chemicals and materials will eventually become COâ‚‚ again, which is then again a resource. Doing so, using renewable energy, as we point out in the manuscript, essentially harvests such renewable energy into the material world.

We sincerely hope that the presented list of available compounds is soon obsolete, as research and development in the area led by teams of creative chemists and engineers will have made many more chemicals and materials from COâ‚‚ accessible.

Is there a concern that people will see these and think we don't need to reduce COâ‚‚ emissions because we can make products from it?

This is a very valid point, one which was also raised during the review process. Let's be clear: COâ‚‚ utilization will only be one factor, besides reducing fossil emissions and carbon capture, to address the climate crisis.

We want to be really clear that what we have outlined here are the many transformations of COâ‚‚ that are currently possible, but that the decisions about what should be done must address more complex criteria, such as the source of COâ‚‚, the type of catalyst used, the energy balance, and other life cycle factors. Ignoring these important factors can result in doing the right things the wrong way; in other words, converting waste COâ‚‚ into valuable products but simultaneously creating unintended consequences.

So, the goal of this manuscript is not to judge what should or should not be done but rather to raise awareness of all the fantastic work on converting COâ‚‚ into something useful that already exists. Then, when implementing such reactions, we do have to make sure we do the right things right. For example, if more COâ‚‚ is generated and released than is incorporated during the process, or a toxic catalyst was used to do so, then the problem might have been made worse. So, there is a need to be thoughtful.

What do you hope will be the biggest takeaway from the study?

The big hope is that chemists, scientists, regulators, and anyone interested will look at this and say, "Oh, wait a minute. It is possible to convert COâ‚‚ into useful materials!" In the manuscript, we have cited examples of reactions for various materials and provided resources for those interested in looking into this in greater detail.

As we outline in the manuscript and our very own Professor Paul Anastas has said, "We can only hope that in a few years' time, this list of possible products we provided is very much outdated, and that one would have to create a whole new tree image to capture the progress in the field."