Scientists show single catalyst can perform first step of turning CO2 into fuel in two very different ways

SLAC
Their work aims to bridge two approaches to driving the reaction – one powered by heat, the other by electricity – with the goal of discovering more efficient and sustainable ways to convert carbon dioxide into useful products.

Virtually all chemical and fuel production relies on catalysts, which accelerate chemical reactions without being consumed in the process. Most of these reactions take place in huge reactor vessels and may require high temperatures and pressures.

Scientists have been working on alternative ways to drive these reactions with electricity, rather than heat. This could potentially allow cheap, efficient, distributed manufacturing powered by renewable sources of electricity.

But researchers who specialize in these two approaches – heat versus electricity – tend to work independently, developing different types of catalysts tailored to their specific reaction environments.

A new line of research aims to change that. Scientists at Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory reported today that they have made a new catalyst that works with either heat or electricity. Based on nickel atoms, the catalyst accelerates a reaction for turning carbon dioxide into carbon monoxide – the first step in making fuels and useful chemicals from CO2.

The results represent an important step toward unifying the understanding of catalytic reactions in these two very different conditions with distinct driving forces at play, said Thomas Jaramillo, professor at SLAC and Stanford and director of the SUNCAT Institute for Interface Science and Catalysis, where the research took place.

“This is a rarity in our field,” he said. “The fact that we could bring it together in one framework to look at the same material is what makes this work special, and it opens up a whole new avenue to look at catalysts in a much broader way.”

The results also explain how the new catalyst drives this key reaction faster when used in an electrochemical reactor, the research team said. Their report appeared in the print edition of Angewandte Chemie this week.

A new avenue for catalyst discovery

For their experiments, the team chose a catalyst Koshy recently synthesized called NiPACN. The active parts of the catalyst – the places where it grabs passing molecules, gets them to react and releases the products – consist of individual nickel atoms bonded to nitrogen atoms that are scattered throughout the carbon material. Koshy’s research had already determined that NiPACN can drive certain electrochemical reactions with high efficiency. Could it do the same under thermal conditions?

A ball-and-stick illustration of a single nickel atom (green) bonded to nitrogen atoms (blue) on the surface of a carbon material. The arrangement allows the nickel atoms to catalyze two types of reactions involved in making fuel from CO2.

This illustration shows one of the active sites of a new catalyst that accelerates the first step in making fuels and useful chemicals from carbon dioxide. The active sites consist of nickel atoms (green) bonded to nitrogen atoms (blue) and scattered throughout a carbon material (gray). SLAC and Stanford researchers discovered that this catalyst, called NiPACN, works in reactions driven by heat or electricity – an important step toward unifying the understanding of catalytic reactions in these two very different reaction environments. (Greg Stewart/SLAC National Accelerator Laboratory)

To answer this question, the team took the powdered catalyst to SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL). They worked with Distinguished Staff Scientist Simon Bare to develop a tiny reactor where the catalyst could expedite a reaction between hydrogen and carbon dioxide at high temperatures and pressure. The setup allowed them to shine X-rays into the reaction through a window and watch the reaction proceed.

In particular, they wanted to see if the harsh conditions inside the reactor changed the catalyst as it facilitated the reaction between hydrogen and CO2.

“People might say, how do you know the atomic structure didn’t change, making this a slightly different catalyst than the one we had previously tested in electrochemical reactions?” Koshy said. “We had to show that the nickel reaction centers still look the same when the reaction is finished.”

That’s exactly what they found when they examined the catalyst in atomic detail before and after the reaction with X-rays and transmission electron microscopy.

Going forward, the research team wrote, studies like this one will be essential for unifying the study of catalytic phenomena across reaction environments, which will ultimately bolster efforts to discover new catalysts for transforming the fuel and chemical industries.

Parts of this study were carried out at the Stanford Nano Shared Facilities, the Canadian Center for Electron Microscopy and the Center for Nanophase Materials Sciences (CNMS) at DOE’s Oak Ridge National Laboratory. CNMS and SSRL are DOE Office of Science user facilities. Major funding came from the DOE Office of Science, including support from the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub.

Citation: David M. Koshy et al., Angewandte Chemie, 16 April 2021 (10.1002/anie.202101326)

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