Think Positively About Carbon Dioxide

The greenhouse gas promises to become an attractive feedstock for fuels and chemicals

By Seán Ottewell, Editor at Large

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A future based on low carbon economics is going to rely on technologies that provide innovative ways of dealing with carbon dioxide, the most-prevalent greenhouse gas. One of the fastest growing areas is the use of novel catalysts to convert the waste gas into useful fuels and chemicals.

Industrial interest in such catalysts definitely is growing. An important indication of this is the formation late last year of CO2 Value Europe, Brussels, Belgium. Its mission is to promote the development and market deployment of sustainable industrial technologies that convert carbon dioxide into valuable products — in particular, as a source of non-fossil feedstock for the chemical industry. Already, 43 industrial and research organizations, including Solvay and Praxair, have signed up.

The organization’s president, Stefanie Kesting, put its aims into context: “The responsible management of carbon dioxide emissions is one of the burning topics of our days. Converting it into sustainable chemicals, fuels or other materials has enormous potential and now reaches the maturity level which is needed for real impact. Therefore, we want to leverage the collective intelligence of our members across the traditional boundaries of industrial sectors to identify which carbon capture and use technologies make the most sense from both a climate and economic perspective, and how those can be brought to market at a large scale.”

Progress in catalysis underpins such initiatives. Here’s a rundown on some notable developments.

Fortuitous Find

At the U.S. Department of Energy’s Oak Ridge National Laboratory (ORNL), Oak Ridge, Tenn., scientists are taking advantage of a chance discovery in October 2016. At that time, the team was working with a catalyst made of carbon, copper and nitrogen. A voltage applied to a solution containing the catalyst, together with carbon dioxide dissolved in water, resulted in a mixture containing mainly ethanol with a yield of 63%.

“We’re taking carbon dioxide, a waste product of combustion, and we’re pushing that combustion reaction backwards with very high selectivity to a useful fuel. Ethanol was a surprise — it’s extremely difficult to go straight from carbon dioxide to ethanol with a single catalyst,” noted Adam Rondinone, senior staff scientist at the ORNL Center for Nanophase Materials Sciences, at the time.

Investigations revealed that the catalyst’s novel performance stems from its nanoscale structure, which consists of copper nanoparticles embedded in carbon spikes (Figure 1). It also was found that this nano-texturing approach obviates expensive or rare metals such as platinum that limit the economic viability of many catalysts.

Since then, the team has been working to improve the catalyst’s performance.

“It’s still the same catalyst, although we have made changes to how it is synthesized in order to lower the cost and improve durability. Although we can’t divulge the details of those improvements yet, we are confident that the catalyst will last long enough in a commercial setting to be useful. We have also removed the silicon wafer that was used as a substrate in 2016,” says Rondinone.

The 63% yield of ethanol remains the same. However, Rondinone believes improvement will be possible when a larger system that can recycle byproducts such as hydrogen and carbon monoxide is engineered. “We have improved the activity of the catalyst, or the ‘current density’ so that it essentially works faster, although there is still a lot more work to be done on that topic,” he adds.

Another topic under investigation is deliberately making the heavier hydrocarbons that sometimes now appear, although not in high amounts, in the reaction product. “The ability to see heavier products suggests that a pathway is there, if we can find a way to exploit it,” he notes.

Alongside this ongoing chemistry work, the team also has spent the last year studying and working to improve the application of the catalyst in an industrial setting.

“This is a very different project from the basic science work. For industrial application, we need to understand the durability and tolerance of the catalyst for contamination, and we need to make it large and cheaper than lab scale, and we need to get the current density as high as possible in order to minimize capital cost. There are many different approaches to understanding and mitigating the challenges of commercial application, and while we’ve made progress, we still have room for improvement,” explains Rondinone.

He reckons the group is about a year from the transfer of the technology into a commercial lab, and that technical developments still will be needed after that point:“A small-scale pilot could be initiated within a year, if things continue to go well.”

The catalyst could have great potential when using stored electricity generated by wind and solar power, the team believes. A recent study carried out by the Tippie College of Business at the University of Iowa, Iowa City, Iowa, concluded that the wind farm approach in particular has great business promise, but it also identified areas needing improvement first.

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