hide
Free keywords:
Mesoporous materials; Cu–Ce–O catalysts; Hard-template; CO oxidation
Abstract:
Highly ordered mesoporous Cu–Ce–O catalysts with different Cu contents have been synthesized by using ordered mesoporous silica KIT-6 as a hard template. The mesostructural order of the negative replica is influenced by the ratio of Cu to Ce. Using XRD, HR-SEM, TEM and EDX analysis, it was found that the ordered mesostructures of the nanocomposites degenerate with increasing Cu concentration, due to CuO leaching during the template removal process and a phase separation at high Cu concentration. Cu ions can replace Ce-ion in the structure of CeO2 at Cu concentrations below 40 mol%. However, the Cu concentration in the final materials is lower than expected from the ratio used in the synthesis. The activity in preferential oxidation of CO in H2-rich gases (PROX) was tested at a space velocity of 60,000 mL h−1 gcat−1. The activity of the mesoporous catalysts increases with the concentration of Cu and becomes stable for Cu concentrations higher than 20 mol%. A CO conversion around 100 % can be attained with Cu0.20Ce0.80O2 as catalyst at 160 °C. The exit CO concentration can be as low as 70 ppm under these conditions. The CO2 selectivity can reach 100 % at low temperature (60 – 80 °C). Direct loading of CuO on the surface of mesoporous CeO2 leads to large CuO crystals and correspondingly low activity. The influence of the pretreatment atmosphere on activity was also studied. Oxidation–reduction–reoxidation cycling can improve the catalytic activity of the catalysts.
