A model study of the hydrogenation of CO over polycrystalline iron

• Published in: Surface science 1979-01, Vol.88 (1), p.269-283
• Main Authors: Krebs, H.J., Bonzel, H.P., Gafner, G.
• Format: Article
• Language: English
• ISSN: 0039-6028; 1879-2758
• DOI: 10.1016/0039-6028(79)90579-X

The hydrogenation of CO was investigated on an initially clean Fe foil in a CO/H 2 mixture at a pressure of 100 kPa (1 atm) and temperatures of 460–750 K. This study was carried out in an apparatus combining a UHV system with Auger and X-ray photoemission spectroscopy capabilities and a differential microreactor operated at 100 kPa pressure. The catalytic Fe foil could be moved between the UHV analysis statlon and the reactor in 45 sec without grossly disturbing the gas flow in the reactor. The mixing ratios of CO/H 2 were 1 : 100, 1 : 20 and 1 : 4. Reaction products were detected by gas chromatography. The main results of this study were: (1) The reaction products were predominantly methane and alkenes; (2) the activation energy for methanation was 21 kcal/mole; (3) the reaction rate for hydrocarbon formation increased initially with time and then stayed either constant or decreased with time where the rate of decrease became larger with higher temperature or CQ/H 2 ratio; (4) two forms of carbon can be distinguished in the surface, “carbidic” (atomic) and “graphitic”, of which only the former can be readily hydrogenated; (5) the initial increase in the rate of hydrogenation is due to the formation of a “carbidic” carbon layer as evidenced by Auger spectroscopy while the following decrease in rate is due to graphite formation on the Fe surface; (6) higher molecular weight products are formed with increasing CO/H 2 ratio.