The conversion profile of CO over CoFeZnNiGa as a function of the temperature is shown in The dependence of CO conversion on the flow rates was studied and the results are shown in Figure (b). As the space velocity was increased from10,000 -40,000 h -1 (GHSV), no effect was observed on the CO conversion profile and temperature. It concludes that external diffusion (mass transfer) has a limited role on the catalytic activity. This is partially due to the fact that HEA nanoparticles do not contain any macroscopic porosity (as its free-standing nature).