Morphology-Engineered Highly Active and Stable Ru/TiO2 Catalysts for Selective CO Methanation.

Ru/TiO2 catalysts exhibit an exceptionally high activity in the selective methanation of CO in CO2- and H-2-rich reformates, but suffer from continuous deactivation during reaction. This limitation can be overcome through the fabrication of highly active and non-deactivating Ru/TiO2 catalysts by engineering the morphology of the TiO2 support. Using anatase TiO2 nanocrystals with mainly {001}, {100}, or {101} facets exposed, we show that after an initial activation period Ru/TiO2-{100} and Ru/TiO2-{101} are very stable, while Ru/TiO2-{001} deactivates continuously. Employing different operando/in situ spectroscopies and ex situ characterizations, we show that differences in the catalytic stability are related to differences in the metal-support interactions (MSIs). The stronger MSIs on the defect-rich TiO2-{100} and TiO2-{101} supports stabilize flat Ru nanoparticles, while on TiO2-{001} hemispherical particles develop. The former MSIs also lead to electronic modifications of Ru surface atoms, reflected by the stronger bonding of adsorbed CO on those catalysts than on Ru/TiO2-{001}.