Correlation of structural characteristics with catalytic performance of CuO/CexZr1−xO2 catalysts for NO reduction by CO

NO reduction by CO reaction was studied over a series of CuO/CexZr1−xO2 catalysts with different copper loadings and Ce/Zr molar ratios to evaluate the correlation of their structural characteristics with catalytic performance. These catalysts were investigated in detail by means of thermogravimetric analysis (TGA/DSC), X-ray diffraction (XRD), Raman spectroscopy, high-resolution transmission electron microscopy (HR-TEM), electron paramagnetic resonance (EPR), UV–vis spectroscopy, X-ray photoelectron spectroscopy (XPS) and H2-temperature-programmed reduction (H2-TPR) and in situ Fourier transform infrared spectroscopy (FTIR). The results demonstrated that the ceria-rich (pseudocubic t″) phase could disperse and stabilize the copper species more effectively and resulted in stronger interaction with copper than the zirconia-rich (t) phase. Furthermore, compared with the zirconia-rich phase, the synergistic interaction of copper with ceria-rich phase easily promoted the reduction of copper species and support surface oxygen, as well as the activation of adsorbed NO species. Therefore, CuO/Ce0.8Zr0.2O2 catalyst exhibited the higher activity for NO reduction than CuO/Ce0.5Zr0.5O2 and CuO/Ce0.2Zr0.8O2. A surface model was proposed to discuss these catalytic properties. The copper species at the interfacial area did not maintain an epitaxial relationship with CexZr1−xO2, while could penetrate into the CexZr1−xO2 surface lattice by occupying the vacant site on the exposed (1 1 1) plane. The type and coordination environment of copper species were different in ceria-rich and zirconia-rich phases surface, and their stabilities were related to the lattice strains.

Copper species could incorporate into the vacant sites on the exposed (1 1 1) plane of ceria–zirconia, and its stronger interaction with ceria-rich phase determined the higher activity than zirconia-rich phase.Figure optionsDownload high-quality image (160 K)Download as PowerPoint slide