Combining Cu-SSZ-13 with TiO2: promotion of urea decomposition and influence on SCR

Abstract

Urea is applied as an ammonia source for SCR in diesel vehicles, but incomplete urea decomposition may lead to insufficiency of NH₃ and deposition of solid by-products. To improve the urea decomposition activity of Cu-SSZ-13 SCR catalysts, Cu-SSZ-13 was combined with TiO₂ nanoparticles by a simple impregnation method. TiO₂/Cu-SSZ-13 composites exhibited lowered decomposition temperatures of urea and related solid by-products. Thus, the composited catalysts showed higher NO_x conversion and a lower amount of urea-related deposits than unmodified Cu-SSZ-13 in a simulated urea deposition scenario. The superiority of the urea decomposition activity of the composited catalysts was maintained upon 800 °C hydrothermal aging due to stabilized anatase over the catalysts according to XRD and Raman spectroscopy. H₂-TPR, UV-vis, and STEM revealed the formation of Cu–Ti–O species due to Cu–Ti interactions, which was adverse to SCR activity, but no extra hydrothermal aging effect was observed on the composited catalysts compared with unmodified Cu-SSZ-13. This work showed the potential to improve the low-temperature urea-SCR performance of Cu-SSZ-13 via TiO₂ modification.