Using light to turn carbon dioxide into useful methane

One way to stem our carbon dioxide emissions is to trap the gas and turn it into chemicals, fuels, and other useful products. Korean researchers have now reported a simple way to produce methane from carbon dioxide using sunlight and common metals.

Why turn one greenhouse gas into another? It would mean recycling carbon dioxide already being pumped into the air. The methane could be used, reducing the need to dig for more natural gas, or it could be stored.

The method mimics photosynthesis, the process by which plants use sunlight, water, and carbon dioxide to produce energy. Researchers have for many years been trying to develop an artificial photosynthesis process that is energy-efficient, uses low-cost, easily available catalysts, and producing a useful fuel.

Many such efforts in the past have used catalysts made of titanium dioxide, mixed with other metals like platinum and catalyst. The result is usually hydrogen. Earlier this year, a Swiss team reported copper and tin-oxide based catalyst that efficiently turns carbon dioxide into carbon monoxide, which can then be turned into fuels.

The new work, reported in Nature Communications, converts carbon dioxide into 99 percent pure methane. The team from the Korea Advanced Institute of Science and Technology used a catalyst made of zinc oxide and copper oxide. They first made microscopic zinc oxide spheres, similar to those found in sunscreen, and then grew copper oxide crystals on the spheres. Then they added these zinc oxide-copper oxide particles to carbonated water.

When sunlight hits the particles, it triggers a reaction that splits carbon dioxide into carbon and oxygen. The carbon combines with hydrogen in water and forms methane, which is the main ingredient in natural gas.

The researchers say that further studies will be required to understand the details of the reaction mechanism. The process would also need to be made much more efficient and faster if it is to be commercially viable.

Source: Kyung-Lyul Bae et al. Colloidal zinc oxide-copper(I) oxide nanocatalysts for selective aqueous photocatalytic carbon dioxide conversion into methane. Nature Communications. 2017.

Image: Rishi Bandopadhay /Flickr

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