Recent publications claimed a significant catalytic effect of nickel nanoparticles on the hydration of CO2 to carbonic acid. Others have claimed that such catalysis can significantly accelerate the overall process of CO2 capture by mineralization to CaCO3 from aqueous solution. Having repeated the experiments as closely as possible, we observed no catalytic effect of Ni nanoparticles. Numerical modelling revealed that hydration is not the slowest reaction in the chain ending with mineralization; hence its catalysis cannot have a significant effect on CaCO3 formation. (C) 2017 Elsevier Ltd. All rights reserved.