Carbon capture that could turn a profit

A catalyst that turns CO2 into carbon monoxide could curb greenhouse emissions while also providing a useful commercial gas. Viviane Richter explains.

Carbon dioxide from coal-fired power plants is the greenhouse gas most responsible for climate change. – livecal / getty images

Carbon dioxide is a climate supervillain – hard to capture and even harder to lock away. But instead of trying to banish the greenhouse gas to an underground prison, why not reform it?

Chemists at the University of California in Berkeley have developed a catalyst that turns carbon dioxide from a costly waste product into a valuable resource. Their catalyst converts CO2 into carbon monoxide. While that’s not a gas you’d want to breathe in, it is a useful raw material industry already uses to manufacture plastics and fuels.

Matthew Hill, a material scientist at CSIRO, says he’s impressed by the catalyst’s “dramatic” performance. The Berkeley team published their discovery in Science in August.

But the world is still not relinquishing its dependence

on cheap coal

Before humanity became addicted to coal a couple of hundred years ago, CO2 levels in the atmosphere were around 280 parts per million. Today, they are nudging 400 ppm and still rising sharply. But the world is still not relinquishing its dependence on cheap coal. Carbon capture and storage (CCS) is one answer. Last year the world’s first commercial carbon-capture power plant opened at Boundary Dam in Canada. The plant’s flue gases are bubbled through large vats of amine solution that trap the CO2. It’s an expensive process. Costs at Boundary Dam are offset by selling the gas to a nearby oil company where it is used to drive petroleum out of the ground. But that strategy won’t work everywhere. “We need an alternative,” Hill says.

So Christian Diercks, joint leader of the new study, decided to convert the CO2 into carbon monoxide (CO), a “foundation molecule” used to manufacture plastics and diesel.

Carbon monoxide, when mixed with hydrogen, can be used to make diesel fuel – zenstock / getty images

Nearly 20 years ago, chemists discovered how to use chemicals called cobalt porphyrins to convert CO2 into CO. Known as electrocatalysts, they pluck an oxygen molecule from every passing CO2 molecule when an electric current is applied to a solution. Unfortunately, these electrocatalysts are only stable in organic solvents that are environmentally harmful. In water they tend to clump, making them slow and inefficient.

So Diercks used some chemical wizardry to make the electrocatalysts soluble and stable in water. He reinforced the cobalt porphyrin molecules by loosely weaving them together to form tall, interlocked stacks.

Locked in this scaffold, the catalyst resists clumping while channels between the loose weave leave room for CO2 to slip in. When the team coated the interwoven chemical on to an electrode, then dipped it in water, each porphyrin turned CO2 to CO at the rate of 290,000 molecules a second. That’s a 26-fold improvement over the previous catalyst. The material was also very stable, powering on undiminished for the full 140 hours it was tested.

Diercks has only made milligram quantities of the catalyst so far, and says at this point it is impossible to calculate what the scale-up costs would be for a power plant.

But Hill remains optimistic about the catalyst’s potential to limit CO2 emissions. “If you can turn that CO2 into a commodity that has value associated with it – that could be the tipping point,” he says.

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