Comparative study of ZSM‐5 supported transition metal (Cu, Mn, Co, and Fe) nanocatalysts in the selective catalytic reduction of NO with NH₃

Abstract

H‐ZSM‐5 was modified with transition metals (including Fe, Cu, Mn, and Co) by homogeneous deposition precipitation (HDP) method and tested as catalyst for the selective reduction of NO with ammonia (NH3‐SCR). The selectivity to N2 was higher than 95% in all the nanocatalysts and the NO conversion over nanocatalysts decreased in the following sequence Cu‐ZSM‐5 > Mn‐ZSM‐5 > Co‐ZSM‐5 > Fe‐ZSM‐5 at 200‐300°C. The Cu‐ZSM‐5 catalyst showed the highest catalytic activity, 95% of NO conversion at 300°C, among the catalysts investigated. The nature of the active sites was characterized by BET, TEM, H2‐TPR, and NH3‐TPD. Characterization results revealed that acidity and the redox properties of the catalysts play an important role in achieving high activity for NH3‐SCR reaction. The highest catalytic activity of Cu/ZSM‐5 can be correlated to easy reducibility of Cu species and strong acidic sites created by the Cu species. © 2017 American Institute of Chemical Engineers Environ Prog, 36: 1049–1055, 2017

Experimental and DFT analysis of the acid and reduction properties of Fe-Cu/ZSM-5

“…The total acidity of all loaded samples increased with respect to the ZSM-5 support, indicating the prevalence of extra-framework deposition. It has been observed before an increase in acidity due to the Lewis sites of deposited transition metals [1,18]. The deposition of Fe create new metallic Lewis acid sites that shifts the second desorption peak from 440 to 470 • C. The Fe-Cu samples with 1% (w/w) Cu or less can be fitted using three peaks, and an increase in the strength of the strong acid sites is observed with increasing Cu content, indicating that the metallic Lewis acid sites from Cu deposition have stronger acidity than the Brønsted acid sites from the zeolite and the metallic Lewis sites from Fe.…”

“…However, two peaks have been observed at around 180 and 250 • C in previous studies of Cu deposited in ZSM-5. No general consensus was found for the species being reduced and these peaks have been attributed to CuO oxides in the external surface, Cu 2+ ions in ion-exchange positions, large copper particles in the pores and Cu dispersed in the ZSM-5 support [18,58,60].…”

“…It was found that the tuning of the reductive and acid properties of Fe with Cu was essential for good results [1,5]. The Fe-Cu/ZSM-5 catalysts were also reported to be active for N 2 O decomposition [6][7][8][9][10][11], NO x reduction [12][13][14][15][16][17][18][19], glycerol conversion [20], ethanol conversion [5,21], benzene oxidation [22,23] and methane oxidation [24,25]. The properties of Fe-Cu/ZSM-5 for these reactions have been extensively studied with experimental methods.…”

Nature of the interactions between Fe and Zr for the methane dehydroaromatization reaction in ZSM-5

“…The peak at 440 C is assigned to Brønsted acid sites from the zeolite. Finally, the peak at 600 C is attributed to strong Lewis acid sites from the Fe impregnation [13,47]. The effect of ZreFe mixing at various Zr/Fe ratios in the desorption temperatures and the acidities (obtained through Gaussian peak fitting) are shown in Table 1.…”

Enhanced Catalytic Performance of Hierarchical MnOx/ZSM-5 Catalyst for the Low-Temperature NH3-SCR

“…The temperature window of traditional commercial catalyst (V 2 O 5 -WO 3 (MoO 3 )/TiO 2 ) is 300-400 • C, and low-temperature NH 3 -SCR catalysts, which can be placed downstream of the desulfurizer and electrostatic precipitator, have attracted increasing attention in recent years [2]. Research on the low-temperature NH 3 -SCR reaction using transition metal oxides (MnO x [3], FeO x [4], CuO x [5], CeO x [6]) as the active components has become widespread. Among these metal oxides, MnO x exhibits excellent low-temperature catalytic activity, which can be attributed to the variable valence states of manganese and oxygen species [7].…”