In Situ FT-IR Studies on the Mechanism of Selective Catalytic Reduction of NO_x by Propene over SnO₂/Al₂O₃ Catalyst

Abstract

The mechanism of the selective catalytic reduction (SCR) of NOx by propene over SnO2/Al2O3 catalyst in the presence of oxygen has been investigated using in situ Fourier transform infrared (FT-IR) spectroscopy. In situ IR measurements indicate that acetate and formate, which are the derivatives of the partial oxidation of propene, play a crucial role in the formation of NCO by reacting with the reactive monodentate nitrate species. The resulting NCO species subsequently reacts with NOx to form N2. The presence of oxygen substantially contributes to the partial oxidation of propene and thus shows a promoting effect for the NOx reduction.

Promoting Effect of CeO2 on NO x Reduction with Propene over SnO2/Al2O3 Catalyst Studied with In situ FT-IR Spectroscopy

“…Over the two catalysts, both the formate (1376, 1392 and 1590 cm -1 ) and acetate (1462 cm -1 ) bands decreased on exposure to NO + O 2 for 30 min, while the band intensities due to monodentate nitrate (1249 cm -1 and 1550 cm -1 ) and bidentate nitrate (1303 cm -1 ) increased. It should be noted that over the CeO 2 -SnO 2 /Al 2 O 3 catalyst, the acetate band almost disappeared after exposing to NO + O 2 for 30 min, indicating that the presence of CeO 2 promotes the reaction rate between the acetate and nitrate species, which is an important step in the HC-SCR over SnO 2 /Al 2 O 3 catalyst [16]. It also indicates that over the CeO 2 -SnO 2 /Al 2 O 3 catalyst, acetate is more reactive than formate.…”

“…Based on the FT-IR studies, we have proposed a simplified reaction scheme for the NO x reduction with propene over SnO 2 /Al 2 O 3 catalyst [16]. Therein, the reaction starts with the formation of both adsorbed nitrates via NO oxidation by O 2, and formate and acetate species via the partial oxidation of propene.…”

“…However, the mechanistic cause of the promoting effect of CeO 2 is still unclear. We have investigated the HC-SCR mechanism over SnO 2 /Al 2 O 3 catalyst using in situ FT-IR spectroscopy and proposed that hydrocarbonderived species (formate and acetate) and nitrate species are crucial ad-species in the HC-SCR [16]. It is expected that the addition of CeO 2 will affect the formation and consumption rate of these surface species, and hence the HC-SCR activity of SnO 2 /Al 2 O 3 catalyst.…”

An investigation of the surface intermediates of H2-SCR of NO over Pt/H-FER

“…However, many problems were encountered in the application of NH 3 -SCR technology [3,4], such as catalyst deterioration caused by the ammonium sulphate deposition, ammonia slip, air heaters fouling, and high running cost [5][6][7]. In the past decades, various hydrocarbons [8][9][10][11][12][13][14] have been studied as reductant for the purpose of removing NO x in excess oxygen, which was expressed as HC-SCR, whereas their poor activity and selectivity under low temperature towards the aimed reaction make this technology hardly developed. Recently, hydrogen [15][16][17][18][19][20][21][22] has been proved to be effective reductant for NO x reduction in excess oxygen because of its high activity towards NO reduction and zero emissions of greenhouse gases in the reaction.…”

“…Hamada et al [9][10][11] have investigated the SCR of NO by C 3 H 8 (C 3 H 8 -SCR) over H-MFI and Al 2 O 3 , and proposed that NO 2 plays an important role for the apparent reaction in the following route: The C 3 H 8 -SCR was started by NO oxidization to NO 2 , and NO 2 produced by the reac-tion then reacted with C 3 H 8 to yield N 2 over the catalysts. Woo and co-workers [12] have investigated the SCR of NO by C 3 H 6 over SnO 2 /Al 2 O 3 using in situ Fourier transform infrared spectroscopy (FTIR), and suggested that the reaction begins with formation of adsorbed nitrate species, which are produced by NO oxidation. Mechanism of H 2 -assisted C 3 H 8 -SCR over Ag-MFI has also been investigated by Shimizu et al using FTIR spectroscopy [13].…”