The effect of the crystalline phase of alumina on the selective CO oxidation in a hydrogen-rich stream over Ru/Al2O3

We prepared Ru catalysts supported on various aluminum oxides with different crystalline phases, viz. α-Al2O3, κ-Al2O3, γ-Al2O3, η-Al2O3, δ-Al2O3 and θ-Al2O3, by the incipient wetness method and applied them to the selective CO oxidation in a hydrogen-rich stream. For comparison, the complete CO oxidation in the absence of H2 was also carried out over the same catalysts. Ru/α-Al2O3 showed the highest CO conversion among the tested catalysts, especially at low temperatures, irrespective of the presence of H2. For all of the catalysts, the catalytic activity for CO oxidation was much suppressed in the absence of H2 compared with that in the presence of H2. Several techniques: N2 physisorption, inductively coupled plasma-atomic emission spectroscopy (ICP-AES), X-ray diffraction (XRD), CO chemisorption, temperature-programmed oxidation (TPO), temperature-programmed reduction (TPR), temperature-programmed desorption (TPD) of CO2 with mass spectroscopy and transmission electron microscopy (TEM) were employed to characterize the catalysts. The least amount of chemisorbed CO and CO2 was obtained at room temperature over Ru/α-Al2O3. The least amount of O2 was chemisorbed during TPO and the oxidized Ru species could be fully reduced in the presence of hydrogen at the lowest temperature over Ru/α-Al2O3 among the Ru/Al2O3 catalysts. Ru/α-Al2O3 can reduce a high inlet concentration of CO to less than 10 ppm even in the presence of H2O and CO2 over a wide temperature range.