In situ DRIFTS study during C2H4-SCR of NO over Co-ZSM-5

Abstract

The formation of surface intermediates and their reactivities with some reactant gases during the selective catalytic reduction of NO with ethylene (C 2 H 4-SCR) over Co-ZSM-5 was investigated systematically by in situ Diffused Reflectance Infrared Fourier Transformed Spectroscopy. Some new IR bands relevant to the surface intermediates formed in the title reaction were identified. The results show that formate species, formed during the partial oxidation of ethylene over Co-ZSM-5, is reactive towards nitrates to yield formyl nitro compound, an intermediate critical for the formation of cyanide and isocyanate species by further reacting with nitrates. Kinetics analysis suggests that the cyanide and isocyanate at different sites vary in reactivity towards nitrates. The Co 2+-CN and Al 3+-NCO species subsequently react with nitrates for final production of N 2 , CO 2 and H 2 O, however, the-CN bound to Brønsted and Lewis acid sites show poor reactivity towards a flow of NO+O 2 /He. On the basis of these investigations, a proposed reaction mechanism explains the formation and roles of all intermediates detected by IR spectroscopy in this study.

The Role of Active Sites of CoH-ZSM-5 Catalysts for the C2H4-SCR of NO

“…As shown in Fig. 5 [7] were observed for the reduced sample. Thus, we speculate that the formation of -CN and -NCO species follow different pathway in the two systems.…”

“…Thus, we speculate that the formation of -CN and -NCO species follow different pathway in the two systems. It has been corroborated that the formation of -CN and -NCO species was attributed to the reaction between formate and various nitrates with a formyl nitro compound (HCONO 2 ) as an intermediate [7]. Comparing the spectrum a with b in Fig.…”

“…According to our previous work [7], various nitrates are key intermediates for the C 2 H 4 -SCR of NO. Thus, the differences of surface intermediates over various catalysts would contribute to the understanding of the functions of Co sites.…”

“…Since the early work of Held and Li [1,2], Co-ZSM-5 is reported to be an active catalyst for the selective catalytic reduction of nitrogen oxide with hydrocarbons (HC-SCR) and extensive research has been devoted to the investigation of reaction mechanism [3][4][5][6]. According to the literatures and our previous study [3][4][5][6][7], a mechanism for the HC-SCR of NO over Co-ZSM-5 was proposed. The reaction begins with the formation of nitrates and carboxylate species.…”

Enhanced Low-Temperature Activity of Ag-Promoted Co-ZSM-5 for the CH4-SCR of NO

“…Total flow rate = 100 mL min -1 , GHSV = 6,000 h -1 (Co, Ag loading = 3 wt%, the presence of Ag facilitated the NO oxidation to nitrates. According to Sadovskaya et al [26] and Chen et al[27], nitrates are key reactive intermediates in the SCR of NO by hydrocarbons. The efficient formation of nitrates on Co, Ag-ZSM-5 catalyst could be the main reason for excellent activity of the catalyst.…”