New Insights into NH<sub>3</sub> Oxidation and N<sub>2</sub>O Formation Over Cu-SSZ-13: Comparison of NH<sub>3</sub>-SCO and NH<sub>3</sub>-SCR
Weihang Zhang, Xing Fan, Qingyu Si, Ruowen Liu, Jingwen Miao, Liyun Song, Jian Li
Abstract
Cu-SSZ-13 catalyst is highly active for both NH 3 -SCO and NH 3 -SCR of NO x . NH 3 conversion and N 2 selectivity were over 98% at 225–500 °C during NH 3 -SCO, while NO x conversion and N 2 selectivity remained above 91 and 98%, respectively, at 150–500 °C during NH 3 -SCR. N 2 O formation showed bimodal behavior with increasing temperature during both processes, with higher amounts of N 2 O produced in the NH 3 -SCR process. Increasing the NO feed concentration enhanced the conversion of NH 3 at low temperatures while promoting the formation of N 2 O at both low and high temperatures. Complete removal of NO x and excessive NH 3 can be achieved at low temperatures (e.g., 250 °C) by coupling NH 3 -SCR and NH 3 -SCO over the Cu-SSZ-13 catalyst. O 2 is necessary for both NH 3 oxidation and NO x reduction. Increasing the O 2 content favored NH 3 oxidation, leading to increasing NH 3 conversion at low temperatures during NH 3 -SCO and decreasing NO x conversion at high temperatures during NH 3 -SCR. N 2 O selectivity increased with increasing O 2 during both low- and high-temperature NH 3 -SCO and NH 3 -SCR processes. NH 3 oxidation over Cu-SSZ-13 follows the two-step mechanism: partial NH 3 is first oxidized to NO and N 2 O, and the formed NO is reduced by the remaining NH 3 to N 2 and N 2 O. Nonselective NH 3 oxidation (NSNO) and catalytic reduction (NSCR) contribute to N 2 O formation at both low and high temperatures.