A microcatalytic investigation was conducted in a tubular fixed bed continuous reactor of the methanation reaction over some nickel and promoted nickel supported catalysts. In carbon deposition studies using stoichiometric quantities of hydrogen and carbon monoxide at temperatures circa 322°C it was indicated that the mechanism of deactivation of the catalyst by carbon deposited on the surface was an activated transformation to an unreactive carbon phase. On catalysts prepared by the incipient wetness technique, the unreactive phase could be hydrogenated at 450°C, while on catalysts prepared by the coprecipitation technique it could not. Platinum and ruthenium promoters increased the activity and resistance to deactivation of nickel catalysts. Lanthanum promoter increased the activity but increaseed the rate of deactivation. Potassium and silver promoters decreased the activity markedly. The reduction technique employed was found to have a significant influence on the rate of deactivation. Catalyst characterisation by scanning electron microscopy, X-ray photoelectron spectroscopy and nitrogen porosimetry indicated that the amount of carbon deposited on the surface was small. Multiple reflectance infrared spectroscopy suggested that the mechanism of CO methanation is the stepwise addition of hydrogen atoms to active surface carbon. Kinetic studies performed in the reactor indicated that the rate limiting step in the mechanism of CO methanation is the hydrogenation of surface carbon. The rate of reaction was best described by power law type empirical rate expressions.
|Date of Award||1982|