Supported ruthenium catalysts for selective methanation of carbon oxides at very low COx/H2 ratios

A group of supported ruthenium catalysts was prepared and tested in methanation of small COx amounts (1000-5000 ppm) in hydrogen-rich streams. Low (66 m(2)/g) and high (440 m(2)/g) surface area graphitized carbons and three oxide materials: magnesia (94 m(2)/g). alumina (225 m(2)/g) and an Mg-Al spinet (96 m(2)/g) were used as supports for the metal and ruthenium carbonyl was used as the Ru precursor. The catalysts were characterized by the chemisorption technique, using O-2 and CO as adsorbates. The studies of COx methanation (flow reactor, atmospheric pressure) have shown that some of the supported ruthenium catalysts exhibit high activities referred to the metal mass. The catalytic properties of ruthenium surfaces expressed by TOFs proved to be dependent on the kind of support material and metal dispersion. In general, the Surface-based reaction rates are the higher, the lower the Ru dispersion (fraction exposed FE), which suggests a dominant role of ensembles of contiguous surface planar Ru atoms. For high metal dispersions (FE = 0.73-0.8), the following sequence of TOFs was obtained: Ru/Al2O3 > Ru/MgAl2O4 > Ru/MgO > Ru/C, both for CO and CO2 hydrogenation. The highly loaded alumina-based system (Ru15/Al2O3) proved to be significantly more active than the commercial nickel-based catalyst, both in terms of TOFs and reaction rates referred to the metal mass. (c) 2008 Elsevier B.V. All rights reserved.