Image: Penn State University

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Researchers at Penn State University, US, claim to have made "dramatic improvements" to the process of converting carbon dioxide into methanol fuel by combining two metals - palladium and copper - to develop a new catalyst.

The development could be a step towards achieving what researcher Chunshan Song describes as 'the holy grail for combating climate change', and "even better than carbon-neutral or renewable fuels", where fuels are made from carbon dioxide using renewable energy in a process that essentially recycles carbon dioxide.

Walnut to football field: finding the most efficient catalyst

A key factor in converting carbon dioxide to methanol was finding a good catalyst so that methanol could be produced at an efficient rate.

Using the palladium-to-copper atomic ratio range of 0.3 to 0.4, the combination of palladium and copper is said to have yielded the most efficient conversion of methanol from carbon dioxide using nanoparticles of the catalyst dispersed on a porous support material that increased the surface area of the catalyst.

With a catalyst the size of a walnut, the internal surface area of the catalyst can cover the area of a football field, the researchers explain.

The study also found that the new formulations, using the precise atomic ratio of the two metals, increased the rate of methanol formation by three times over palladium alone and by four times over copper alone, representing a significant improvement over previous methods.

Cat-and-mouse conversion

Comparing the process to a cat catching a mouse on the surface of a catalyst, the researchers point out that for the conversion to occur, both carbon dioxide (the cat) and hydrogen (the mouse) were required.

Additionally, the ideal conditions were also needed for the 'cat' to successfully catch the 'mouse': if the cat is not able to reach the mouse, or conditions slow it down, then the cat has less success.

But by combining the two metals, it not only lowers the energetic requirements to speed up the reaction of carbon dioxide and hydrogen, but also alters the reaction pathways to produce a more desired product with higher energy efficiency, the researchers explain.

"Conventional studies focused on copper but that doesn't yield efficient results," said Chunshan Song, a Professor at the Department of Chemical Engineering and Director of the EMS Energy Institute at the Pennsylvania State University. "It's the same for palladium. But putting palladium and copper together creates a unique surface structure that shows a special selectivity to creating methanol from carbon dioxide. This study provides the fundamental insights into the very synergetic effects of using these two metals together."

The process

To create methanol, researchers pumped hydrogen and carbon dioxide into a sealed chamber of a reactor vessel packed with the catalyst and heated the contents to between 356 and 482 degrees Fahrenheit.

The carbon dioxide hydrogenation process works by decomposing water to create a hydrogen gas using renewable energy, which then bonds with the carbon dioxide on the surface of the catalyst to create methanol.

'Holy grail' for beating climate change

According to Song, the efficient production of fuels and industrial chemicals from carbon dioxide using renewable energy is "the holy grail for combating climate change because the fuels are even better than carbon-neutral or renewable fuels".

The process essentially converts greenhouse gases to fuels that emit carbon dioxide when burned. When combined with the capture of carbon dioxide from the environment, it amounts to recycling carbon dioxide instead of creating or avoiding it.

"Our current energy system largely relies on carbon-based fossil energies," Song remarked. "Even renewable fuels such as biomass, biogas and organic waste, they are all carbon-based. But in the future, where does carbon come from? If we begin using carbon from carbon dioxide, we can recycle it, create a sustainable carbon-based energy cycle, and then we stabilize the carbon dioxide concentration in the atmosphere. That's why I'm passionate about this."

Recent research developments involving methanol

Last year, researchers at the University of Liverpool claimed a breakthrough in the direct conversion of carbon dioxide and methane into liquid fuels using a non-thermal plasma process said to offer a 'promising and attractive' alternative for the synthesis of fuels.

Also in the UK, scientists in Wales claimed to have created methanol from the air around us - from methane using simple catalysis that allows methanol production at low temperatures using oxygen and hydrogen peroxide.