Periodic operation applied to the kinetic study of CO2 methanation

Abstract

Periodic operation was applied to the CO2 methanation reaction at 383 K on 2% Ru/TiO*. A continuous feed recycle reactor combined with a diffuse reflectance infrared cell and a mass spectrometer allowed to follow simultaneously the gas phase CO, and CH4 as well as the adsorbed species (CO), and (formate),. Experiments consisting of periodic variations of CO2 in the hydrogen feed showed response curves with maxima/minima shifted in time in the sequence CO,, (formate) a + (CO) =--f CH,. Similar delays measured for the (CO) a formation and hydrogenation indicate that both of these processes are limiting the overall reaction rate. A kinetic model was proposed and verified under periodic conditions. The main experimental trends, which are pronounced time lags between CO;?, (CO) d and CH4, could be described satisfactorily.

In-situ surface and gas phase analysis for kinetic studies under transient conditions The catalytic hydrogenation of CO2

“…The whole set-up, formed by the fixed bed and the infrared cell is described by Marwood et al [6], and is called afterwards recycle reactor. 4 g of catalyst were placed in the fixed bed while 0.06-0.08 g were placed in the DRIFTS cell.…”

“…The Rco values are either smaller or equal to the overall reaction rate Rcn 4, calculated from the steady-state kinetic equation [6].…”

“…Furthermore, (CO) a was detected and identified as a major metal-adsorbed intermediate ( [3,4] and [5]). At 383 K, on a Ru/TiO 2 catalyst, the CO 2 steady-state methanation rate can be described by a simple power law where the reaction rate is almost of order 1/2 in hydrogen concentration and is inhibited by the reaction product water [6].…”

Transient drift spectroscopy for the determination of the surface reaction kinetics of CO2 methanation

“…The apparatus for the steady-state experiments consisted of a recycle reactor linked to the DRIFTS cell and is described elsewhere (Marwood et al, 1994). CO2 (99.995%), H2 (99.9999%) and He (99.9999%) gases were used after passing through Oxisorb traps that reduce oxygen impurity levels to less than 0.1 ppm.…”

“…A CO2 (CO),, ~ CH4 sequence can be established. In additional experiments (Marwood, 1994) it was verified that CH 4 is not adsorbed on the catalyst and CO adsorption from the gas phase is fast compared to (CO),, formation from CO2. (CO coverage was found to follow the gas phase concentration in transient experiments without any time delay.)…”