A fundamental approach to the carbon dioxide problem

Professor William McNamara is drawing inspiration from nature to tap the potential of CO2 as a fuel.

By studying how plants harness sunlight to power cellular processes, Chemistry Professor William McNamara and his students are aiming to turn carbon dioxide into fuel. (Photo by Stephen Salpukas)

As policymakers and advocates gather to celebrate National Clean Energy Week, scientists across the world are sleuthing out ways to generate sustainable, clean energy. From wind farms to electric cars to solar fields to nuclear power plants, there are many paths to explore.

Alongside these familiar clean energy solutions, another idea has emerged: What if we could transform one of the most infamous greenhouse gases - carbon dioxide - into a viable source of energy?

At William & Mary, inorganic chemist and professor William McNamara is probing the fundamental mechanisms of this process, and he's taking his inspiration from nature.

His work is among multiple efforts across campus to safeguard the environment and the communities that depend on it. William & Mary is currently celebrating the Year of the Environment, a yearlong observance to advance sustainability efforts on campus and expand the university's impact around the world.

Imitating nature's design

"I've always been fascinated by how we can harness the energy of the sun to power processes on Earth," McNamara said. "The advent of solar power has made huge strides in this field, but there are many more avenues to pursue."

Specifically, McNamara is interested in studying something called artificial photosynthesis.

"The idea behind this is to understand how plants convert energy from photons, which are tiny packets of solar energy, into fuel," he said. "And then to figure out how humans can mimic this process to produce our own types of fuel."

McNamara's previous research focused on splitting water (H2O) into its respective molecular components to create hydrogen fuel, mimicking a reaction plants perform early on in photosynthesis.

But recently, he's turned to investigate a later part of the process, by which plants convert CO2 into glucose, a sugar that serves as their primary energy source. He hopes studying nature's design will help him create an analogous process to turn carbon dioxide into fuels that human engines would want to consume.

While plants use enzymes to perform the necessary chemical steps for fuel, humans need to make their own enzyme-like compounds, or, as chemists call them - catalysts.

"Catalysts do exactly what their name implies - they make chemical reactions happen more easily and more quickly," said McNamara. "The types of catalysts we're working on are modeled off of an enzyme in plants called carbon monoxide dehydrogenase, or CODH for short."

CODH plays an important role in the conversion of carbon monoxide to CO2 and vice versa. For McNamara, its chemistry holds valuable clues for CO2 conversion. Critical to CODH's conversion process are metals, specifically iron and nickel, that lie at the heart of its catalytic center.

"Plants use elements like iron and nickel because they are abundant in nature," explained McNamara. "As scientists, we have access to a much bigger selection of metals, including things like ruthenium and iridium, but they are much less abundant in nature and much more expensive."

By using catalysts formed around iron and nickel, McNamara's group hopes to lay the groundwork for a CO2 conversion process that, if scaled, would be more cost-effective than using rare-earth metals.

In addition to a metal at the reaction site, McNamara's catalysts contain ligands - molecules that attach to the metal and form what is called a coordination complex. To explain the function of ligands, he illustrates the essential chemistry that enables all mammals to breathe.

"Mammals breathe by taking in oxygen, which then binds to a metal-ligand coordination complex called, you guessed it, hemoglobin," said McNamara. "Now, if we just had hunks of iron traveling around in our bloodstream, they wouldn't be carrying oxygen. But when iron is bound to a heme ligand inside hemoglobin, its properties are tuned so that it can bind and release oxygen under specific conditions. So, by making specific ligands, we can regulate the reactivity of that metal center."

In McNamara's catalysts, ligands tune the metal center so it can transfer electrons to CO2, converting the gas into molecules like carbon monoxide or formate. These, in turn, can be transformed through additional steps into fuels such as methane, the primary component of natural gas.

Having just recently launched into CO2 research, McNamara's lab, which includes 11 undergraduates working on three related projects, has already produced several catalysts formed around iron and nickel that have successfully reduced CO2.

"Our next steps are to understand what the specific products of this reaction are and how much of them are out there," he said. "In so doing, we hope to gain an understanding of the selectivity of these catalysts. This will help us glean insight into the overall mechanism of the process. These studies will lay the foundation for accessing larger hydrocarbon molecules in the future."

For a cleaner future

While burning natural gas, or any of the other fuels that could be created from CO2, would create more CO2, scientists like McNamara point to the renewable aspect of using carbon dioxide as a fuel.

"The advantage with this technique is that our initial fuel input would be CO2, not some non-renewable gas pumped from below the Earth's surface," said McNamara. "So you're recycling carbon already in the atmosphere rather than adding new carbon molecules into the cycle."

The idea is less about eliminating CO2 entirely and more about treating it like recyclable plastic - using it over and over instead of pulling new material from the ground. While the opportunities for fuel conversion are exciting, many other applications of CO2 derivatives exist.

"There are a host of compounds, think carbon monoxide and formate, with important industrial and pharmaceutical applications that you can make by reducing CO2," said McNamara. "The potential benefits of this type of green chemistry approach are really widespread."

"The advantage with this technique is that our initial fuel input would be CO2, not some non-renewable gas pumped from below the Earth's surface. So you're recycling carbon already in the atmosphere rather than adding new carbon molecules into the cycle."

William McNamara

While some labs and commercial enterprises have made impressive progress on CO2 conversion, McNamara highlights the multifaceted challenges that need to be solved before carbon dioxide can be deployed as an effective and accessible fuel.

"You need to think about how to scale your reactions, how to keep your catalysts stable and doing their job - not just for minutes or hours, but for years - how to store and transport the reactive species," he said. "It's a problem that demands a very multidisciplinary approach."

Thankfully, an army of specialists in materials science, engineering, inorganic chemistry and beyond is working to solve this challenge, tackling it from different angles. Each project, each reaction is a step toward a cleaner future. And McNamara, along with his students, is excited to be part of this movement.

"I'm really proud to contribute to research with real environmental significance," said Yuanheng Zhuang '28, who started working with McNamara the summer after his freshman year. "I'm learning to think like a researcher, use ingenuity to overcome problems and work efficiently in the lab. Gaining those skills while working on a project I'm passionate about is a unique opportunity - and one of the reasons I came to William & Mary."

Catherine Tyson

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