Homogeneous MnOx–CeO2 pellets prepared by a one-step hydrolysis process for low-temperature NH3-SCR

Abstract

To investigate the possibility of using a one-step hydrolysis process to prepare selective catalytic reduction (SCR) catalyst, a one-step hydrolysis process was introduced to fabricate the MnOx–CeO2 (HP) catalyst. Scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Brunauer–Emmett–Teller analysis (BET) were used to characterize the catalysts. The results showed that Mn, Ce and O were uniformly distributed on the bulk and the surface of MnOx–CeO2 pellets (MnOx–CeO2 (HP)). According to XPS analysis, manganese and cerium species co-existed in the oxidation states of Mn4+/Mn3+ and Ce4+/Ce3+ in the MnOx–CeO2 pellets. The BET and XRD results indicated that the interaction between Mn and Ce as “solid solution” occurred in MnOx–CeO2 (HP). It was demonstrated that the uniform MnOx–CeO2 pellets obtained via the hydrolysis process showed higher SCR activity than those prepared via co-precipitation (MnOx–CeO2 (CP)) and combustion (MnOx–CeO2 (CB)) in the temperature range of 80–260°C. Uniform distribution of Mn and Ce, lower atomic binding energies, higher Mn4+/Mn3+ ratio, higher Ce4+/Ce3+ ratio, higher specific surface area, higher Oα/Oβ ratio and the defect in the “solid solution” resulted in higher NO conversion for MnOx–CeO2 (HP) than those for MnOx–CeO2 (CP) and MnOx–CeO2 (CB). Therefore, the one-step hydrolysis process is proven to be a good method for synthesizing MnOx–CeO2 for low-temperature SCR.