Computational Insights into the Mechanism of the Selective Catalytic Reduction of NO_x: Fe- versus Cu-Exchanged Zeolite Catalysts

Abstract

We computationally investigate the mechanism of the reduction half-cycle of the selective catalytic reduction of nitrogen oxides with ammonia. We compare both Fe- and Cu-exchanged zeolite catalysts and aim at exploring all accessible reaction pathways. From our calculations, a comprehensive picture emerges that unifies several previous mechanistic proposals. We find that both for Fe and for Cu catalysts different reaction pathways are feasible but some of the possible reaction pathways differ in these two cases. Our computational results provide a basis for the interpretation of in situ spectroscopic investigations that can possibly distinguish the different mechanistic pathways.

Detection of key transient Cu intermediates in SSZ-13 during NH3-SCR deNOx by modulation excitation IR spectroscopy

“…4 Overall, we nd that the observed intermediates have previously been postulated as key species in the catalytic cycle proposed by Janssens et al, although we do note that such species appear in a number of proposed cycles to date. 10,43,44…”

Selective catalytic reduction of NO with NH3 over Cu-exchanged CHA, GME, and AFX zeolites: a density functional theory study

“…52,53 The formation of the Cu I -NOOH species is slightly exothermic relative to the NO + -Cu I -OH − species, which is the same as the previous report. 51 The energy barriers for the H 2 O formation are 131, 147, and 153 kJ mol −1 for cha, gme, and aft. The following desorption of H 2 O is endothermic, which exhibits the same reaction energy of −48 kJ mol −1 for the three frameworks.…”

“…site has been proposed for the cha framework, however, the detailed information such as the energy barrier is still absent. 13,21,51 All energies shown in these diagrams are measured with respect to the isolated zeolites and the NO/NH 3 molecule. Spin multiplicities of intermediates and transition states are shown in Fig.…”

Effect of Calcination Temperature on the Activation Performance and Reaction Mechanism of Ce–Mn–Ru/TiO2 Catalysts for Selective Catalytic Reduction of NO with NH3

“… 17 Interestingly, these mechanisms are all premised on the occurrence of the Mars–van Krevelen (M–K) mechanism that after the reaction between the reaction gas and the oxygen on the surface of the catalyst, the partly reduced surface is re-oxidized by O 2 . 18 , 19 The M–K mechanism is a decisive factor affecting the activation of the reaction gas by the catalyst. Unfortunately, many researchers are not good at using the M–K mechanism to prepare catalysts and to explore the role of this mechanism in the field of SCR.…”