A mechanistic investigation on the selective catalytic reduction of NO with ammonia over the V-Ce/Ti-PILC catalysts

Abstract

The Ti-pillared clay-supported vanadia−ceria (yV4Ce/Ti-PILC, y was the V weight percentage (wt%), Ce weight percentage=4wt%) samples were prepared using the impregnation method. The catalytic activity for the selective catalytic reduction of NOx with NH3 (NH3-SCR) decreased in the order of 1V4Ce/Ti-PILC >4Ce/Ti-PILC >2V4Ce/Ti-PILC >1V/Ti-PILC >1V4Ce/Clay > Ti-PILC > Clay, with the 1V4Ce/Ti-PILC sample exhibiting the best activity (NOx conversion >90% at 280–450°C). Physiochemical properties of the samples were investigated by means of XRD, N2 absorption-desorption, SEM, H2-TPR, NH3-TPD, XPS, and in situ DRIFT techniques. The vanadia was uniformly dispersed on the Ti-PILC support, while the ceria were mainly present in CeO2. The Ti-pillared support was suitable for dispersing the V-Ce composite oxides. The strong interaction between vanadia and ceria led to increased H2 consumption and high-temperature reduction. The Ce4+/Ce3+ and V5+/V4+ redox cycle (V4++Ce4+↔V5++Ce3+) accounted for the excellent NH3-SCR catalytic performance of the 1V4Ce/Ti-PILC sample. The doping of a proper amount of vanadia could promote formation of Ce3+ on the surface of 1V4Ce/Ti-PILC, and the formed Ce3+ could generate a more amount of the chemisorbed oxygen species that favored the NH3-SCR reaction. Furthermore, the 1V4Ce/Ti-PILC sample possessed high catalytic acidity and strong NH3 adsorption ability, which were responsible for high NO conversion in a wide range of temperatures. The NH3-SCR reaction on the 4Ce/Ti-PILC and 1V4Ce/Ti-PILC samples obeyed the Langmuir–Hinshelwood (L–H) and Eley-Rideal (E–R) mechanisms, with the former being dominant.