Given the widespread desire to reduce greenhouse gas emissions, many observers expect carbon capture technology to become as common as nitrogen oxide (NOx) and sulphur oxide (SOx) smokestack scrubbers have already become on large industrial sites. 

Nevertheless, there is no ready equivalent of such scrubbers to remove CO2 from flue gas. Although the molecular sieves offered by zeolites have a demonstrated ability to remove trace gases, including CO2, they do not function well under humid conditions, such as those found in a post-combustion stream. Meanwhile, metal organic frameworks (MOFs) offer uniform micropores, high surface areas and greater stability but they also rapidly decompose in the presence of water. “You have to repeat the gas adsorption and desorption process millions of times over the life of a typical power plant, which is 30 to 50 years,” says University of Ottawa chemistry professor Tom Woo. “So these materials have to be very stable and that’s been the problem with MOFs for these applications.” 

Woo recently co-authored a paper in Science Advances introducing a nickel-pyrite MOF that could fill this tall order. The single-ligand, ultra-microporous material was shown to have a high CO2 saturation capacity and good selectivity for this gas at high pressure, as well as remaining hydrolytically stable. 

Woo points out that these properties are not best suited for post-combustion capture of CO2 but are instead ideal for pre-combustion CO2 capture, which promises to be more efficient. This approach calls for an entirely different plant design, one which creates a high-pressure stream of CO2 and hydrogen before any fuel is consumed. The former can be absorbed by the MOF and released for storage, while the latter can be burned without releasing any carbon. 

Woo originally modelled the behaviour of the new MOF in his Ottawa laboratory, while colleagues in India and Europe were able to test a physical sample to confirm his predictions. The publication has already attracted interest from companies that could make use of this material, including an operator of coal-fired generating stations and a firm that collects methane from landfills.

Woo cautions that the search for sequestration sorbants is still under way but this latest discovery provides an important step towards materials that can be used in practice. “If you can find a high-performing material that’s ultra-stable, then it would be amongst the most cost-effective ways to capture carbon,” he says.