Selective oxidation of CO in hydrogen-rich stream over Cu-Ce catalyst promoted with transition metals

摘要

Cu-Ce/γ-Al_2O_3 catalysts promoted with Co were tested for the low temperature selective oxidation of CO in excess hydrogen. The effects of Cu-Ce composition, Co as a dopant, stoichiometric ratio (λ = 2O_2/CO), water vapor and CO_2 on the selective oxidation of CO to CO_2, O_2 consumption and selectivity of O_2 to CO oxidation as a function of temperature are presented. Also, the catalytic properties of the catalysts were investigated by using X-ray diffraction, CO-/H_2-temperature programmed reduction, temperature programmed oxidation, CO-/CO_2-/H_2O-temperature programmed desorption (TPD). Small addition (0.2 wt) of Co onto the Cu-Ce/γ-Al_2O_3 brought large increase in selective CO oxidation activity. In the presence of either CO_2 (13 vol%) or H_2O (10 vol%) in the reformed gas feed, both Cu-Ce/γ-Al_2O_3 and Cu-Ce-Co/γ-Al_2O_3 showed decreased activity in CO oxidation at low temperatures, especially, under 200℃. Compared with the Cu-Ce/γ-Al_2O_3. however, the Cu -Ce-Co/γ-Al_2O_3 gives higher resistivity for the CO_2 and H_2O. From the CO_2/H_2O-TPD results, it could be explained that the main cause for the decrease in catalytic activity with CO_2 and H_2O in the feed may be attributed to the competitive adsorption of CO and CO_2 as well as the blockage of the active sites by water vapor at low reaction temperatures.