Carbon Capture and Utilization (CCU) technologies certainly represent a promising way not only to reduce carbon dioxide impact on climate change, but also to convert CO2 into added-value products/chemicals. The majority of CCU technologies, amine scrubbing and mineralization included, play around the dissolution of carbon dioxide in aqueous solution and the corresponding pH-dependent equilibria between CO2(aq), carbonic acid (H2CO3), bicarbonate ion (HCO3-) and carbonate ion (CO32-). Since the early studies on CO2 dissolution, it was clear that the hydration (the multisteps process responsible for the formation of carbonic acid) was the rate limiting step of the reaction, confirmed over the years by experimental and computational studies. In nature, CO2 hydration reaction is catalysed by Carbonic anhydrase (CA), a zinc-based metalloenzyme able to accelerate the CO2 hydration and dehydration rate. During the last decade, it has been suggested that nickel nanoparticles (NiNPs) can also propel the hydration of adsorbed CO2 into carbonic acid. However, the catalytic effects of NiNPs on CO2 hydration in water has been recently questioned in literature, also because a clear molecular understanding of the process is still missing. Here we present a combined experimental and computational (ab-initio molecular dynamics) study showing that, contrary to some common knowledge in literature, NiNPs does not catalyze the formation of carbonic acid in solution, but rather the CO2 capture step. Indeed, the NiNP surface prefers to coordinate CO2 rather than water to avoid a (negative) overcharging of the NP. The computational simulations are in agreement with the CO2 hydration kinetics experiments. These results indicates that the apparent catalytic effect of NiNP in the carbonation of adsorbed CO2 in aqueous solution is the results of an higher efficiency of the solution in capturing CO2, rather than a catalytic conversion of CO2 in carbonic acid on the surface of the NiNPs.

Unexpected mechanism for CO2 hydration promoted by nickel nanoparticles, a combined experimental-computational approach

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