Deactivation of Co/γ-Al2O3 in CO methanation studied by transient isotopic experiments: The effect of Co particle size

Abstract SSITKA coupled with transient isothermal (TIH) and temperature-programmed hydrogenation (TPH) were used to investigate the influence of Co particle size (dCo=11-21 nm) and time-on-stream, TOS (up to 25 h) on important kinetic parameters of CO methanation at 230 oC on Co/γ-Al2O3. TOFCO and TOFCH4 were independent of dCo and decreased with TOS. The θCO and θCHx (active CO-s and CHx-s) slightly increased with dCo as opposed to θCxHy (inactive species), which remained practically constant. On the contrary, θCHx and θCxHy largely decreased and increased, respectively, while θCO stayed practically constant with TOS. An inverse D-KIE independent of dCo was estimated by a novel 13CO/D2-SSITKA experiment, reported for the first time to the best of our knowledge. The reason of catalyst deactivation was the decrease of kCHx (hydrogenation of -CHx) likely because of the influence of -CxHy on the bonding of active species and on θH (a decrease was determined).