Synthesis and characterization of Co-K/Kx Ti2O5 as novel NOx storage and reduction (NSR) catalyst

Abstract

In the present work, a novel NOx storage and reduction (NSR) catalyst Co-K/Kx Ti2O5 was synthesized via impregnation of K2Ti2O5 with Co(CH3COO)2 aqueous solution. This NSR catalyst exhibited a high NOx storage capacity (ca. 3.2 μmol/g) at 400°C and has the potential to significantly decrease the Pt loading (as low as 0.1 wt%). Not only Co, but also some other metals including Pt, Ce, and Fe were studied. Among them Co showed the best performance and the optimal loading was determined as 7.5 wt%. Characterizations by X-ray diffractions (XRD), scanning electron spectroscopy (SEM), and transmission electron spectroscopy (TEM) confirmed that during the synthesis, certain amount of inter-layer K+ ions were exchanged out from K2Ti2O5 bulk to the surface and work as the NOx adsorption sites; and in the meantime, Co3O4 nanoparticles were doped on the surface which work as active species for NO oxidation. In order to understand the NOx adsorption pathways, NOx adsorption on Co-K/Kx Ti2O5 catalyst was performed in different systems including NO, NO+O2, NO2, and NO2+O2. It has been concluded that NO oxidation is a key prerequisite step for NOx adsorption. Co-K/Kx Ti2O5 alone has relatively poor NOx reduction activity, but it can be significantly increased by introducing only 0.1 wt% of Pt. When the temperature was higher than 350°C, no NO and only negligible amount of N2O were produced in the products. © 2013 by American Scientific Publishers.