Selective CO Methanation on Highly Active Ru/TiO₂ Catalysts: Identifying the Physical Origin of the Observed Activation/Deactivation and Loss in Selectivity

Ru /TiO₂ catalysts are highly active and selective in the selective methanation of CO in the presence of large amounts of CO₂, but suffer from a considerable deactivation and loss of selectivity during time on stream. Aiming at a fundamental understanding of these processes, we have systematically investigated the physical reasons responsible for these effects, using catalysts with different surface areas and combining time resolved kinetic and in situ / operando spectroscopy measurements as well as ex situ catalyst characterization. This allowed us to identify and disentangle contributions from different effects such as structural effects, adlayer effects such as site blocking effects and changes in the chemical (surface) composition of the catalysts. Operando XANES / EXAFS measurements revealed that an initial activation phase is largely due to the reduction of oxidized Ru species, together with a distinct change in the Ru particle shape, until reaching a state dominated by metallic Ru species (fraction RuO₂