The Impact of Support Material of Cobalt-Based Catalysts Prepared by Double Flame Spray Pyrolysis on CO2 Methanation Dynamics

Abstract

Methanation is capable of chemical storage of fluctuating renewable energy, which requires fundamental understanding of the dynamics of the kinetic processes taking place on the catalyst surface. In order to elucidate the impact of the catalyst support on the dynamics, Co-based model catalysts were synthesized via double flame spray pyrolysis (DFSP) differing only in the support materials. In particular, Co nanoparticles of identical particle size distributions are supported on SiO2, TiO2 and SiO2-TiO2 mixtures by independent formation of the support and the active metal by means of DFSP. The transient catalyst behavior was studied by step changes of the feed gas composition and the analysis of the reactor response with high temporal resolution, according to the periodic transient kinetics method. It was revealed that H2O adsorption strongly depends on the support with increasing sorption capacity from SiO2, via SiO2-TiO2 to TiO2. The storage of H2O on the support induces a sorption-enhancement effect and thereby promotes the transient CH4 formation rate for Co/TiO2 catalysts. Transient experiments before and after a steady-state operation period under CO2 methanation reveal an unchanging reaction mechanism, while changes in selectivity towards CH4 and CO are observed together with a certain degree of deactivation. Hence, the support material was identified to play a major role in activity, selectivity and deactivation behavior for supported Co catalysts in CO2 methanation.