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Could CO2 be an alternative fuel?

Imagine if we could not only remove CO2 from the atmosphere, but convert it into fuel.

Could CO2 be an alternative fuel? by Laura L. Otto

Can air-polluting carbon dioxide (CO2) emissions be collected and recycled back into fuel? UWM’s Ying Li believes they can, which would make it possible to use fossil fuels with little increase in greenhouse gases.

Conversion of the gas won’t be easy, but Li, an assistant professor of mechancial engineering, has hit on a process that will work – if he can perfect a nanomaterial with exactly the right properties.

I am excited that we are working on the research that could change our world.

Cunyu Zhao, doctoral student

Armed with a CAREER grant from the National Science Foundation, Li is improving the efficiency of a nanomaterial he engineered that could make CO2 recycling scalable.

“You cannot eliminate carbon dioxide unless you convert it into something else,” says Li. His process uses sunlight to power a complex catalytic reaction involving CO2, water and his hybrid nanomaterial. He calls it “artificial photosynthesis” because it converts CO2, water and sunlight into hydrocarbons in a way similar to that of plants.

The result is a sustainable source for hydrocarbon fuels such as methane and methanol – carbon-neutral alternatives to fossil fuels like oil and natural gas.

Doctoral student Cunyu Zhao was a process engineer at a chemical plant in China before coming to UWM to study with Li. Like engineers in U.S. manufacturing plants, Zhao would like to find a way to decrease the amount of CO2 released into the atmosphere without compromising production.

“I am excited that we are working on the research that could change our world,” he says, “and also to see that our experiment results are promising and our ideas are becoming practical.”

The process begins when nanoparticles of the titanium dioxide catalyst that Li has developed absorb sunlight. The high-energy wavelengths of the ultraviolet spectrum excite electrons in the nanoparticles.

CO2 reacts with the electrons, and its carbon and oxygen atoms, together with hydrogen atoms in the water, are coaxed to the catalyst’s surface, where they can be extracted as hydrocarbons.

Li and his lab members are modifying the nanomaterial so that it will enhance the CO2 conversion efficiency and lengthen the lifetime of the catalyst. Their fine-tuning has already improved the stability of the reaction, says Zhao.

The researchers are also performing the reaction at a higher temperature – above the boiling point of water – rather than at room temperature, in a quest to increase the yield of products resulting from the reaction. The increased temperature can be generated sustainably through industrial “waste” heat or the infrared portion of sunlight.

Ultimately, Li hopes to devise a technology that applies his “artificial photosynthesis” to a stationary emission source, like the smokestack of a coal-burning power plant.