Effect of Transition Metal Additives on the Catalytic Performance of Cu–Mn/SAPO-34 for Selective Catalytic Reduction of NO with NH3 at Low Temperature

Abstract

The adsorption of NO, NH 3 , H 2 O, and SO 2 gaseous molecules on different transition metal oxides was studied based on density function theory (DFT), and three better-performing transition metal elements (Fe, Co, and Ce) were selected. Cu-Mn/SAPO-34 catalysts were prepared by impregnation method and then modified by the selected transition metals (Fe, Co, and Ce); the SO 2 resistance experiments and characterizations including Brunner−Emmet−Teller (BET), X-ray Diffraction (XRD), Scanning Electronic Microscopy (SEM), and thermal gravity analysis (TG)-differential thermal gravity (DTG) before and after SO 2 poisoning were conducted. The results showed that the deactivation of the Cu-Mn/SAPO-34 catalyst is ascribed to the deposition of lots of ammonium sulfates on the surface, depositing on the active sites and inhibiting the adsorption of NH 3 . After the modification of Fe, Co, and Ce oxides, the SO 2 resistance of the modified Cu-Mn/SAPO-34 catalyst was significantly enhanced due to the less formation of ammonium sulfates. Among all these modified Cu-Mn/SAPO-34 catalysts, the Cu-Mn-Ce/SAPO-34 exhibited the highest SO 2 resistance owing to the decreased decomposition temperature and the trapper of ceria for capturing SO 2 to form Ce(SO 4 ) 2 , further inhibiting the deposition of ammonium sulfates.Catalysts 2019, 9, 685 2 of 15 be an important oxide component in the SCR reaction, due to the various types of labile oxygen and high oxygen-storage capacity [9]. CuO is found to be highly resistant to SO 2 in the low-temperature SCR reaction due to the activity of CuSO 4 [10]. It is reported that the Mn-Cu/SAPO-34 catalyst displays remarkable hydrothermal stability and good SCR activity in a broad temperature range [11][12][13].It is well accepted that the application of low-temperature SCR catalyst relies not only on the high SCR activity, but also the superior SO 2 resistance due to the fact that the exhaust from the industrial boiler system contains a good amount of SO 2 . However, Mn-based catalysts are proven to be sensitive to SO 2 poisoning. Two main deactivation routes are widely reported. Firstly, SO 2 can be oxidized to SO 3 , which can react with NH 3 and H 2 O to form (NH 4 ) 2 SO 4 and NH 4 HSO 4 ; the former dries powdery, which decomposes at 280 • C [14], but the latter is a kind of corrosive and sticky substance, which decomposes at 390 • C [15], Secondly, MnO x or CuO may react with SO 2 to form stable sulfate species, which can cut off the redox cycle of the catalyst [16] and hinder the adsorption and activation of NO on the surface of the catalyst [17]. As such, the development of Mn-based catalysts with superior SO 2 resistance has attracted wide concern by many researchers.The main method to improve SO 2 resistance is adding other modification metals/non-metals to SCR catalyst. Chang et al. [18] reported that the NO conversion over the SnO x -MnO 2 -CeO 2 catalyst exhibited 60% approximately in the presence of SO 2 and H 2 O, which is much higher than that over MnO 2 -CeO 2 . The promotion effect...

The Resistance of SO2 and H2O of Mn-Based Catalysts for NOx Selective Catalytic Reduction with Ammonia: Recent Advances and Perspectives

“… 83 , 84 Jin et al 81 found that doped Ce was beneficial for reducing thermal stability of NH 4 HSO 4 on the catalyst surface, as shown in Figure 11 . This is also confirmed by Liu et al, 82 who prepared a Ce-Cu-Mn/SAPO-34 catalyst. Moreover, the Ce protects the main active components from being sulfurized, as shown in Figure 12 .…”

“…Mn-based supported catalysts have made some progress. High redox performance, low surface area loss, and excellent acidity can be obtained with the combination of metal modification and support, thus improving the SO 2 and H 2 O resistance of the catalyst. ,,,, The metal oxide, the molecular sieve supports, and the carbon-based supports summarized in the previous section are mainly contained in the carrier. Among metal oxide supports, the TiO 2 is widely used, while the molecular sieve and carbon-based ones have a wide variety and flexible choices.…”

“… XRD pattern of 2% Ce-modified catalyst after SO 2 poisoning. Reprinted with permission from ref ( 82 ). Copyright 2019 MDPI.…”