New catalyst for creating syngas from waste CO2

A CATALYST produced via flame spray pyrolysis can be used to turn waste CO₂ into syngas for use in fuels and feedstocks.

The catalyst has been developed by a team at UNSW Sydney using flame spray pyrolysis (FSP) to make zinc oxide (ZnO) nanoparticles. FSP is a combustion synthesis method where a metal precursor dissolved in a solvent is fed into a flame along with a flow of oxygen where it combusts to create nanoparticles.

ZnO is a cheaper alternative to materials such as palladium, which have been used in the past for previous attempts at this technique. ZnO nanoparticles are traditionally created via a hydrothermal approach but these have lower activity compared to the FSP-made nanoparticles. 

"We don't need to worry about complicated synthesis techniques that use really expensive metals and precursors –  we can burn it and in ten minutes have these particles ready to go,” said Emma Lovell, Lecturer at the School of Chemical Engineering.

The catalyst can then be used to turn CO₂ into syngas via an electrolyser. Most syngas is produced via steam methane reforming, so this new method would reduce the need for fossil fuels while also using waste CO₂.

"Syngas is often considered the chemical equivalent of Lego because the two building blocks - hydrogen and carbon monoxide – can be used in different ratios to make things like synthetic diesel, methanol, alcohol or plastics, which are very important industrial precursors,” said Lovell. "So essentially what we're doing is converting CO₂ into these precursors that can be used to make all these vital industrial chemicals."

"Waste CO₂ from say, a power plant or cement factory, can be passed through this electrolyser, and inside we have our flame-sprayed zinc oxide material in the form of an electrode,” said Rahman Daiyan, Research Fellow at the School of Chemical Engineering and lead author of the study. “When we pass the waste CO₂ in, it is processed using electricity and is released from an outlet as syngas in a mix of CO and hydrogen."

They convert the CO₂ to syngas using simultaneous electrochemical CO₂ reduction reactions and hydrogen evolution reactions. The mix of CO and H₂ in the syngas can be adjusted from the way the nanoparticles are burned with FSP. The metal precursor is fed to the FSP nozzle and by controlling the rate of flow, nanomaterial properties such as crystallinity and surface chemical environment can be controlled. For example, increasing the feed rate increases the size of the nanoparticles. This then allows tuning of the H₂/CO ratio of the syngas by getting the correct balance between CO and H₂ reactions on the surface of the catalyst.

The team has already tested an electrolyser with waste CO₂ containing contaminants, and further work will need to be done to test the technology on flue gas to ensure it can tolerate the conditions. If it is successful, it should be possible to easily scale the process as the catalyst is effective and easy to make, and it should also be possible to retrofit the technology to existing facilities.

Advanced Energy Materials, http://doi.org/d3zr