Carbon monoxide adsorption on a Ru/SiO(2)catalyst was followed by IR spectroscopy to investigate the active sites. Using this catalyst, ammonia synthesis was achieved at 350 degrees C in an N-2/H-2 gas mixture (N-2/H-2 approximate to 3 : 1) for different reaction times. In addition to NH3 other NH, (x = 1,2) species were also observed. CO adsorption after NH3 production was also performed to investigate the change in nature of the active sites. Based on the experimental evidence participation of Ru-0 sites in ammonia synthesis was confirmed and a partial oxidation of the reduced Ru sites during the synthesis was observed. (C) 1999 Elsevier Science B.V. All rights reserved.