Abstract
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/Al 2O 3 catalyst, in CO 2-rich reformate gases by combined kinetic and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements. Based on the correlation between CO ad band intensity/CO ad 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/Al 2O 3, 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 CO 2 dissociation and subsequent methanation. The underlying reasons and consequences for practical applications are discussed.
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