CuO-CeO2 catalysts based on SBA-15 and SBA-16 for COPrOx. Influence of oxides concentration, incorporation method and support structure

Abstract

In this work different variables that can affect the catalytic behavior of CuO-CeO2 supported on mesoporous silica (SBA-15 and SBA-16) were studied. The influence on the COPrOx activity of the relative concentration of the CuO and CeO2 active phase and different impregnation methods in mesoporous support was analyzed. The physicochemical characterization was performed EDS-SEM and TEM-STEM, N2 isotherms, X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS). The incipient wetness impregnation method (IWI) was the better alternative to introduce the active phases compared to solid state impregnation (SSI). In addition, the catalysts based on 2-D structure of SBA-15 were more active and selective than those based in 3-D SBA-16. In general, the high surface area of the supports benefited the dispersion of CuO and CeO2 oxides nanoparticles. All catalysts displayed the preservation of the mesostructure and the formation of nanoparticles of active phases (less than 10 nm) detected by TEM. The best COPrOx catalyst, obtained from the SBA-15 fibers by IWI method, with a relative CuO concentration of 0.2, exhibited XCO ≥ 99% at 175 °C and above 90% in a wide window of temperatures. This catalyst showed an adequate performance in presence of CO2 and H2O and good recovery of CO conversion and selectivity. The analysis by XPS revealed that the majority species were Ce4+, however in some catalysts Ce3+ species are also present, which are associated with vacancies oxygen and favor the redox process. In addition, Cu2+ and Cu+ species are present, the latter recognized as a key site of CO adsorption in the reaction mechanism.