A novel ceria hollow nanosphere catalyst for low temperature NOx storage

Abstract

In this work, a highly active CeO2 catalyst with hollow nanosphere morphology for low temperature NOx storage was prepared by a surfactant-assisted solvothermal reaction. The physicochemical properties of ceria samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption–desorption, H2-temperature programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS) and in situ diffused reflectance infrared Fourier transform spectroscopy (DRIFTS). The as-prepared CeO2 nanosphere possesses excellent NO oxidation capacity, smaller mesopores, better reducibility and more surface Ce3+ content. Compared with CeO2 with nanorod and nanoparticle morphologies, CeO2 nanosphere shows better intrinsic low temperature NOx trapping performance, with a wide operating temperature window (150–300 °C), high NOx adsorption capacity (NAC, 640–745 μmol/g) and high NOx storage capacity (NSC, 250–350 μmol/g). Two reaction pathways are speculated for NOx adsorption on CeO2 nanosphere, including “nitrate route” and “nitrite route”. The thermally unstable surface nitrites formed on the CeO2 nanosphere allow ceria to release more NOx during the desorption process. The present work provides a new ceria morphology for NOx traps, which may become a potential excellent NOx storage material.