On the Support Effect of the CO2 Methanation

Abstract

This thesis addresses the catalyst support effect in the CO2 methanation, specifically the impact of the acid/base properties of the catalyst support. In the first part, support-activity correlations are developed by excluding particle sizes effects of the active component on the catalyst performance. To this end, uniform colloidal Ru nanoparticles are deposited on various support with different acid/base properties. The resulting catalysts are fully characterized regarding their physico-chemical properties by i.e. CO2-TPD accompanied by DRIFTS, TEM, XRD and N2 physisorption. It is demonstrated that oxidic supports that exhibit oxygen vacancies, and particularly rare earth metal oxides, are the most promising support materials for the Ru catalyzed CO2 methanation. By combining catalytic experiments with operando DRIFTS, the high activity of these catalysts can be attributed to support related reaction pathways that occur additionally to a ruthenium-based mechanism. These findings are applied to develop a highly active Ni-Sm2O3 xerogel catalyst system which outperforms an industrial methanation catalysts as well as literature-known systems. Intermediate Ni loadings between 30-40 wt.% offer the best compromise between H2 adsorption and dissociation sites on the metal and CO2 adsorption sites on the oxidic perimeter sites. Yet, the catalysts suffer from deactivation due to the formation of thermally stable carbonates, most likely formed on oxygen deficient sites. Upon a facile regeneration step in H2 the high activity can be fully restored. Lastly, a methodology to precisely control the porosity of Sm2O3 xerogels which can be used to investigate the impact of the structural parameters of the catalyst support.