3346. TEBBOTH, J. A. Decomposition of Carbon Monoxide by Nickel Catalysts. Reaction Mechanism Between 250° and 450°. Jour. Soc. Chem. Ind., vol. 67, 1948, pp. 62-66.
Principal factors involved in the catalytic formation of CH4 from water gas have been described recently. A major difficulty encountered was the progressive deposition of C on the Ni-ThO2-kieselguhr catalyst used. An attempt is made here to ascertain the mechanism of the formation of C and how to minimize it. It was found that unsupported and unpromoted Ni catalysts, derived from precipitated NiCO3, showed little activity for the decomposition of CO at all temperatures between 250° and 450°. The presence of ThO2 and kieselguhr in a Ni catalyst prepared from the precipitate NiCO3 caused a marked increase in the rate of decomposition of CO at the same temperatures. Elementary C formation occurred on Ni catalysts at al temperatures from 250°-450°, being least at 250° and greatest at 325°-350°. The Ni of such promoted and supported Ni catalysts was converted almost quantitatively to Ni3C at 250°. Above this temperature, carbide formation was incomplete. Decomposition of Ni3C in the presence of ThO2 and kieselguhr occurred above 250° and was rapid at 300°. The proportion of C combined as carbide decreased with increasing temperature, but some persisted at 450°. When using promoted and supported catalysts for CH4 synthesis from CO and H2, the conditions prevailing at the inlet end of the catalyst bed were very favorable for elementary C formation. The results were accounted for by 2 reactions: 3 Ni+2 CO=Ni3C+CO3 and Ni3C=C+3 Ni. The latter reaction may have occurred in 2 stages with the formation of a lower carbide Ni6C, but evidence here was incomplete.
----------. See abs. 304.