Ratio of adsorptive abilities for NH3 and NOx determined SCR activity of transition-metal catalyst

Abstract

Transition-metal catalysts were widely used in selective catalytic reduction of nitrogen oxide (NOx). However, seldom work reported the influence of adsorptive abilities of a catalyst for NH3 and NOx on the activity. This work synthesized oxide-state and chelation-state catalysts, and compared them in adsorptive abilities and catalytic activities. As a result, the oxide-state catalyst was more inclined to adsorb NOx than the chelation-state catalyst, and resulted in a lower adsorbed ratio between NH3 and NOx. When the ratio was 0.25 at 100 °C, a removal of 18.5% was obtained. If the ratio was 1.06, the removal was close to zero. Similarly, a low ratio of 0.42 resulted in a removal of 60.2%, far bigger than 21.9% (the ratio = 1.35) at 200 °C. In other words, the oxide state needed less NH3 than the chelation one. When the stoichiometric ratio between NH3 and NO was decreased from 1:1–0.5:1, NO removal of the oxide-state catalyst was only decreased from 60.2% to 31.0% at 200 °C. In comparison, NO removal of the chelation-state catalyst was decreased from 21.8% to 1.3%. The main results of this work help us to understand deeply the catalytic mechanism. This work is also in favor of optimizing running parameters as well as alleviating ammonia slip.