Abstract
Carbon deactivation of a 0.5 wt % Ru/..gamma..-Al/sub 2/O/sub 3/ surface-impregnated catalyst was studied by using a Berty continuous-stirred, gas-solid reactor (CSGSR)-gas chromatograph setup. The experimental variables were as follows: temperature, 473-573 K; pressure, 2-6 atm; weight hourly space velocity, 0.85, 16.5 h/sup -1/; H/sub 2//CO feed ratio, 3 and 2; and synthesis time, 0.5-5 h. Carbon deposited in a synthesis run was measured by integrating the methane evolution profile during catalyst reduction at 723 K in H/sub 2/. Significant amounts of carbon were deposited, increasing to several monolayers during 5-h synthesis periods. The methanation rate decreased as the synthesis continued, while the selectivity for C/sub 2/-C/sub 4/ hydrocarbons showed a maximum during the initial stages of deactivation. The kinetic data could be correlated by assuming both hydrogen-assisted CO dissociation and hydrogenation of surface carbon to be rate determining. The turnover numbers for methanation (N/subCH/4/sub) and carbon deposition (N/C/Ru/sub) are given.
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