New CoO−SiO₂-Sol Pillared Clays as Catalysts for NO<i>_x</i> Conversion

Abstract

New CoO−SiO2-sol pillared montmorillonite (Co−SiM) is synthesized by interlamellar hydrolysis and condensation of tetraethyl orthosilicate (TEOS) in the presence of Co2+ ion via an alkylammonium intercalated montmorillonite. The silicate layers of Na+−montmorillonite are expanded in advance with hexadecyltrimethylammonium cation up to ∼22 Å, followed by reaction with a mixed sol solution of TEOS and CoCl2·6H2O in the presence of n-dodecylamine as a cotemplate. A microporous Co−SiM is obtained after removing the organic templates at 550 °C. The nitrogen adsorption−desorption isotherm for the pillared sample reveals that a large number of micropores are created between the silicate layers, giving rise to a high BET specific surface area (SBET = ∼570 m2/g) and a pore volume (V = ∼0.65 mL/g). According to the X-ray photoelectron and X-ray absorption spectroscopy, the incorporated cobalt species is found to be CoO, which is homogeneously dispersed on the surface of the SiO2 pillars. The Co−SiM exhibits an excellent NO conversion rate of ca. 50% at 200 °C, which continuously increases up to 80% at 500 °C.