Preferential Oxidation of CO in H2-Rich Stream Over Au/CeO2-NiO Catalysts: Effect of the Preparation Method

Two methods, viz., the hydrothermal (HT) and co-precipitation (CP) methods, were used to prepare CeO2-NiO composite oxides; with them as the supports, Au/CeO2-NiO catalysts were prepared by the colloidal deposition method and used in the preferential oxidation (PROX) of CO in H-2-rich stream. Various characterization measures such as N-2 sorption, XRD, TEM, H-2-TPR, Raman spectroscopy and XPS were used to clarify the influence of preparation method on the structure of CeO2-NiO support and the performance of Au/CeO2-NiO catalyst. The XPS and TEM results reveal that the CeO2-NiO(HT) support prepared by hydrothermal method displays a uniform rod-like shape and exposes preferentially the (110) and (100) planes of CeO2, whereas the CeO2-NiO(CP) support prepared by co-precipitation method is composed of nanorods and irregular nanoparticles dominated by (111) facets of CeO2. After deposition of gold, both the Au/CeO2-NiO(HT) and Au/CeO2-NiO(CP) catalysts are alike in the state and size distribution of deposited Au nanoparticles. The H-2-TPR results indicate that the presence of Au strongly promotes the reduction of CeO2 in the Au/CeO2-NiO catalyst. Raman spectra illustrate that the incorporation of Ni ions into CeO2 remarkably increases the amount of oxygen vacancies in the CeO2-NiO supports, especially in CeO2-NiO(HT) prepared by hydrothermal method, which is beneficial to the dispersion and stabilization of gold species. The structure of CeO2-NiO support and catalytic activity of Au/CeO2-NiO in CO PROX is strongly related to the preparation method; Au/CeO2-NiO(HT) exhibits much higher activity than Au/CeO2-NiO(CP). The larger fraction of (110) and (100) CeO2 facets in CeO2-NiO(HT) can promote the dispersion of gold species, formation of oxygen vacancies and migration of oxygen species, which are effective to enhance the redox capacity and activity of the obtained Au/CeO2-NiO(HT) catalyst for CO PROX in H-2-rich stream.