Periodic operation applied to kinetic studies of CO2-methanation

Periodic operation was applied to the CO2 methanation reaction at 383 K on 2% Ru/TiO2. A continuous feed recycle reactor combined with a diffuse reflectance infrared cell and a mass spectrometer allowed to follow simultaneously the gas phase CO2 and CH4 as well as the adsorbed species (CO)a and (formate)a. Experiments consisting of periodic variations of CO2 in the hydrogen feed showed response curves with maxima/minima shifted in time in the sequence CO2, (formate)a --> (CO)a --> CH4. 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 CO2, (CO)a and CH4, could be described satisfactorily.