Boreskov Institute of Catalysis of the Siberian Branch of Russian ...

OP-I-17The activity measurements were completed by a kinetics study by varying the partialpressure of acetylene at constant hydrogen pressure and vice-versa in order to determine theapparent order of reaction. The order towards C 2 H 2 was found to be negative and equal to -1.0 whereas the order toward hydrogen was found to be equal to 1.0. The coverage of thesurface byC 2 H 2 is therefore constant and the rate is only a function of the hydrogen coveragewhich explains the increase of conversion at constant temperature when the hydrogen partialpressure increases.Concentration of surface hydrocarbonaceous deposits accumulated during differenttreatments was also determined by temperature programmed oxidation (TPO). Hydrocarbonoverlayer was observed to form immediately, and its presence appeared to be having ablocking effect only at very high concentration, the decrease of activity being due to the factthat these layers of carbonaceous deposits slow down the diffusion of the reactants towardsthe active sites. A large excess of hydrogen suppressed the formation of carbonaceous laydown and increased the over-hydrogenation of acetylene. Two types of carbon wereidentified, the first one formed at low temperature is not involved in the hydrogenation, thesecond one formed above 300°C is formed by surface carbenes which are key intermediates inthe formation of methane.At the issue of the presentation, a detailed mechanism of the various reactions pathwaysof acetylene hydrogenation on Au/CeO 2 will be presented.References1. S. Ivanova, C. Petit, V. Pitchon, Appl. Catal., A, 267, (2004), 191–201.59