What drives the selectivity for CO methanation in the methanation of CO2-rich reformate gases on supported Ru catalysts? Original Research Article

Aiming at a mechanistic understanding of their selectivity for CO methanation and the underlying physical reasons, we have investigated the selective methanation of CO over two supported Ru catalysts, a Ru/zeolite catalyst and a Ru/Al2O3 catalyst, in CO2-rich reformate gases by combined kinetic and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements. Based on the correlation between COad band intensity/COad coverage and the selectivity for CO methanation over a wide range of CO contents, down to 100 ppm, two different mechanisms are identified for the two catalysts. On Ru/Al2O3, the selectivity results from blocking of active surface sites by adsorbed CO, while for the Ru/zeolite catalyst we relate this to an inherently low activity of the very small Ru nanoparticles for CO2 dissociation and subsequent methanation. The underlying reasons and consequences for practical applications are discussed.