Study on Cerium-Based Catalysts TiCe0.2W0.2O2−δ for Selective Catalytic Reduction of NOx at Low Temperature

In order to meet the increasingly stringent emission regulations for NO_x in the exhaust gas of engines, selective catalytic reduction (SCR) technology is extensively studied and practiced. The key to this technology is the catalyst utilized in the chemical reactions of SCR. It is required to develop the SCR catalyst with good low-temperature performance and a wide active temperature window. A series of Cerium-based metal oxides TiCe_mW_rO_2−δ synthesized by solution combustion synthesis is studied in this paper. The SCR activity test was used to select the catalyst with the best performance. The NO conversion rate of the best catalyst in our studies reached 80% at 150 °C, kept 100% from 200 °C to 420 °C and the N₂ selectivity remained above 95% for 100–500 °C. The SO₂ resistance test was carried out at 250 °C and proved that our catalyst had good SO₂ resistance. During the test, the NO conversion rate slightly decreased while 100 ppm SO₂ was injected, but it remained above 80% for 24 h. The NO conversion rate recovered to the original value when the SO₂ supply was cut off. The N₂ selectivity remained at 100% throughout the process. Catalysts were characterized using BET, XRD, and SEM methods. In-situ DRIFTS method was used to study the reaction mechanism of the TiCe_0.2W_0.2O_2−δ catalyst. It showed that the NH₄⁺ species absorbed on the Brønsted acid played a dominant role in the SCR reactions. The bridge nitrate resulted from the NO absorption and gas phase NO was involved in the reaction. In conclusion, the mechanism studied included two routes of L-H and E-R.

Graphical abstract