Mechanism of propylene effect on the NH3-SCR performance of Cu-SSZ-13 catalyst
Wenqing Ding, Yu Sun, Jingjing Liu, Sen Xue, Xuewang Han, Zidi Yan, Yunbo Yu, Yulong Shan, Hong He
Abstract
The ability of commercialized Cu-SSZ-13 to catalyze the Selective catalytic reduction of NO x by ammonia (NH 3 -SCR) is inhibited in the presence of hydrocarbons. The effect of C 3 H 6 on the performance of Cu-SSZ-13 zeolite catalysts for NH 3 -SCR with various copper loadings and Si/Al ratios (SARs) was investigated in this work. At low temperatures, the competitive adsorption of C 3 H 6 with NH 3 and NO x is the main reason for the performance decline in the low-temperature range. When the temperature was above 250 °C, C 3 H 6 began to be activated, resulting in carbon deposition and propylene ammoxidation , which are both major factors in the reduction of NO x conversion that accompanies C 3 H 6 poisoning. The propylene ammoxidation reaction has a significant influence on the activity due to a shortage of the reducing agent NH 3 , and becomes progressively dominant with increasing Cu loading and decreasing SAR. C 3 H 6 preferably participates in the direct oxidation of C 3 H 6 and the selective catalytic reduction of NO x by C 3 H 6 (C 3 H 6 -SCR) in the high-temperature range, contributing to the suppression of propylene ammoxidation and the restoration of NH 3 -SCR performance, and this phenomenon is facilitated by the increase in Cu loading and SAR. The accumulation of carbon deposits formed after high-temperature activation of C 3 H 6 can affect the low-temperature NH 3 -SCR performance, but the carbon deposits can be burned off in the high-temperature range, thus restoring activity. The overall results can guide the control strategy of after-treatment systems in diesel engines.