Cobalt nanoparticles (10-50 nm) have been prepared by different procedures. Materials produced by reduction of cobalt chloride and nitrate by NaBH4 contain B impurities as borates or borides. They are very active in ethanol steam reforming at 673-773 K with up to 85% hydrogen yield at 773 K. B-free samples obtained by thermal decomposition of Co-2(CO)(8) is slightly less selective to hydrogen, due to its activity in ethanol cracking to methane which is probably poisoned by boron impurities on the other catalysts. B-containing samples are inactive in CO2 methanation and have weak activity in the reverse water gas shift (RWGS) reaction to CO. B-free nanoparticles have high activity in both CO2 methanation and RWGS. However, methanation activity is reduced fast by growth of encapsulating carbon species. These particles however also show quite stable activity in RWGS to CO, attributed to CoO impurities. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.