Correlation of structural characteristics with catalytic performance of CuO/Ce_xZr_(1-x)O_2 catalysts for NO reduction by CO

摘要

NO reduction by CO reaction was studied over a series of CuO/Ce _xZr_(1-x)O_2 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 H_2-temperature-programmed reduction (H_2-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/Ce_(0.8)Zr_(0.2)O_2 catalyst exhibited the higher activity for NO reduction than CuO/Ce _(0.5)Zr_(0.5)O_2 and CuO/Ce_(0.2)Zr _(0.8)O_2. A surface model was proposed to discuss these catalytic properties. The copper species at the interfacial area did not maintain an epitaxial relationship with Ce_xZr_(1-)_xO_2, while could penetrate into the Ce_xZr _(1-x)O_2 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.