# No-CH4-SCR Over Core-Shell MnH-Zeolite Composites
## 3 Results and Discussion
### Catalytic Activity Studies  
NO-CH\({}_{4}\)-SCR reaction results over the catalysts are summarized in Table 2. In the process, NO is converted to N\({}_{2}\) and CH\({}_{4}\) is converted to CO\({}_{2}\) completely. MnH-Y exhibits low NO-CH\({}_{4}\)-SCR activity in the entire test temperature range, which is similar to that over CoH-Y. The maximal NO to N\({}_{2}\) conversion was 61.1% at 773 K over MnH-Beta. This is probably due to the different cation coordination and the different acidity of these two types of zeolites [8; 27; 28]. The cation coordination is influenced by the ligand, crystal field and topological structure of zeolites [28], whereas the acidity depends on the zeolite structure. These two factors collaborate to promote NO conversion to N\({}_{2}\) in NO-CH\({}_{4}\)-SCR [27; 28]. As expected, the NO to N\({}_{2}\) conversion over ZZm-n decreases with the content of MnH-Beta in the zeolite mixtures, and is lower than that over MnH-Beta in the entire test temperature range. NO to N\({}_{2}\) conversions over MnH-ZZs-n are higher than that over ZZm-n in the entire test temperature range, although the relative content of BEA and FAU phase is comparable. Moreover, the methane conversion over MnH-ZZs-n was suppressed because of the different types of Mn\({}^{2+}\) cations and the interaction with acid sites in zeolites. The maximal NO to N\({}_{2}\) conversion over MnH-ZZs-n catalysts has a maximum with the change of zeolite Y phase in the composites. The maximal NO to N\({}_{2}\) conversions are 74.6%, 77.3%, 65.8%, and 46.8%, respectively, over MnH-ZZs-n (n = 1.0, 0.5, 0.3, 0.2). If there is no synergic effect between two zeolites in the composites, the NO to N\({}_{2}\) conversions over MnH-ZZs-n catalysts, such as at T = 773 K or 823 K, should be closed to those over the physical mixtures MnH-ZZm-n. Practically, a significant difference is indicated, particularly in the case of the relative contents of zeolite Y in the composites between 0.2 and 0.5. In all cases, a positive synergic effect for NO to N\({}_{2}\) conversion is observed over the core-shell composite catalysts [18]. To understand the effect of protonic sites in the catalysts, activity tests were performed over MnNa-ZZs-0.5 and MnH-ZZs-0.5 prepared with the same parent Na-ZZs-0.5 zeolite composite. The results in Table 2 show that NO to N\({}_{2}\) conversions over MnNa-ZZs-0.5 and MnH-ZZs-0.5 catalysts are comparable at a temperature below 723 K. Increasing the reaction temperature, NO-CH\({}_{4}\)-SCR activity over MnH-ZZs-0.5 is much higher than that over MnNa-ZZs-0.5. The maximal NO to N\({}_{2}\) conversions are 77.3% at 823 K over MnH-ZZs-n and 55.5% over MnNa-ZZs-n at the same temperature. It is well known that the acidic OHs in zeolites are active in adsorbing and perturbing hydrocarbon molecules, and nitrogen oxides as well [29], the protonic sites promoted NO-CH\({}_{4}\)-SCR. Obviously the synergistic effect between the metal and protonic sites of zeolite is reflected only at a higher temperature in the reaction system. Figure 3: NH\({}_{3}\)-TPD spectra of (**A**) H-zeolite a. H-Y, b. H-Beta, c. H-ZZs-0.3; (**B**) MnH-Zeolite a. MnH-Y, b. MnH-Beta, c. MnH-ZZs-0.3. Table 3 showed the effect of Mn content in the catalysts on the NO-CH\({}_{4}\)-SCR activity. The NO-CH\({}_{4}\)-SCR activity increases considerably over the catalysts incorporated with Mn loadings. However, MnNa-ZZs-n and MnH-ZZs-n exhibited similar activity at a temperature lower than 673 K, indicating the ion-exchange Mn in the zeolite composites play a key role in NO-CH\({}_{4}\)-SCR. As mentioned above, the synergic effect of metal ions and protonic sites resulted in much higher NO-CH\({}_{4}\)-SCR activity over MnH-ZZs-n than MnNa-ZZs-n at a high reaction temperature. The transient response analysis and in situ FT-IR studies, by exploring the surface interactions of isotopic labeled reactants, showed that the reaction follows a Mars-van-Krevelen-like mechanism through the formation of nitrosamide and azoxy intermediates [30].