Mechanistic insights on the reaction behaviors of the acrylonitrile selective catalytic combustion over Cu-based UZM-9

Abstract

In this paper, a series of Cu-based UZM-9 catalysts were prepared via modified aqueous ion exchange and the performance of acrylonitrile (AN) selective catalytic combustion (SCC) over these catalysts were investigated, and further characterized by Ar adsorption-desorption, ICP, XRD, H2-TPR and XPS. Among which, Cu-11.5 catalyst exhibited a complete AN conversion at 270 °C together with N2 selectivity higher than 98% during the whole temperature range when water was present. Meantime, the isolated Cu2+ was the main active sites, which could be reduced to Cu+ during -CN oxidation, then reoxidized to Cu2+ by O2. Besides, the mechanism of AN SCC over Cu-11.5 was systematically investigated by in situ DRIFTS, which revealed that both the temperature and H2O contents could influence the main N-containing intermediate and the reaction mechanism. In low and high temperature region, the reaction followed hydrolysis mechanism. Within medium temperature range, the reaction mechanism of AN oxidation was strongly associated with the water content. Oxidation was dominant at water-free condition, while oxidation and hydrolysis coexisted at relatively low water content (0.3%). When water content reached up to 0.9% or more, hydrolysis was the principal reaction. Finally, the hydrothermal stability of Cu-based UZM-9 catalysts were illustrated.