Cu-ZSM-5 Catalyst Impregnated with Mn–Co Oxide for the Selected Catalytic Reduction of NO: Physicochemical Property–Catalytic Activity Relationship and In Situ DRIFTS Study for the Reaction Mechanism

Abstract

A series of MnCo/Cu-ZSM-5 (MnCo/Cu-Z) catalysts with different Mn/Co ratios for the selective catalytic reduction (SCR) of NO with NH3 were prepared by the combination of ion exchange and impregnation. The physicochemical properties of the catalysts were investigated by N2 adsorption/desorption, X-ray diffraction (XRD), temperature-programmed reduction with hydrogen (H2-TPR), X-ray photoelectron spectroscopy (XPS), and temperature-programmed desorption of NO x (NO x -TPD) and NH3 (NH3-TPD), and the diffuse reflectance infrared Fourier transform (DRIFT) technique was employed for the detection of intermediate species and the study of the mechanism. The introduction of Mn and Co boosts the catalytic activity of the Cu-Z catalyst at a temperature below 200 °C, and the optimum activity was obtained over the Mn1Co2/Cu-Z catalyst. The enrichment of the high-valent metal ion on the catalyst surface and the improvement in the reducibility of metal oxide are responsible for the elevation in the catalytic activity of MnCo/Cu-Z. The bridged and bidentate modes are the prevailing nitrate species on the Cu-Z and MnCo/Z catalysts, respectively, and both of them were detected over the MnCo/Cu-Z catalyst. Furthermore, the DRIFT spectroscopy (DRIFTS) results indicate that, at 150 °C, the bridged nitrate can react with the adsorbed ammonia species, but the bidentate nitrate fails to do. The SCR reaction over the Cu-Z catalyst follows the Eley–Rideal and Langmuir–Hinshelwood mechanisms simultaneously at 150 °C, whereas an overwhelming dominance of the Eley–Rideal mechanism is identified for the MnCo/Z catalyst. As to the SCR mechanism on the MnCo/Cu-Z catalyst, it combines the features of Cu/Z and Mn1Co2/Z.

Discovering Surface Structure and the Mechanism of Graphene Oxide-Triggered CeO2–WO3/TiO2 Catalysts for NO Abatement with NH3

“…In the practical application, water vapor from the internal combustion engine is unavoidable, thus H 2 O was introduced into the test system. The activity of NH 3 -SCR catalysts shows an evident decrease at low temperature (150–250 °C) in comparison with the results obtained in the absence of H 2 O (Figure b), attributable to the competitive adsorption of H 2 O on the surface of catalysts, while NO x conversion increases in the range of 350–550 °C, wherein the CeWTi-3 sample still displays the best catalytic performance in a low-temperature region (<300 °C). NO x conversion is 94% over the CeWTi-3 catalyst at 250 °C, and a wider operational temperature window (NO x conversion above 90%) is achieved from 250 to 500 °C in contrast with the other samples, manifesting a good tolerance to H 2 O.…”

“…Reactant and product concentrations in the effluent were analyzed by an FTIR spectrometer in Antaris IGS (Thermo Scientific). The conversion of NO and NH 3 was determined according to eqs and The turnover frequency (TOF) of NO was estimated on an active center of cerium or tungsten by eq , where P is 0.101 MPa, V is the flow rate of NO (0.375 mL/min), R is 8.314 J mol –1 K –1 , T is the reaction temperature (423, 433, 443, and 453 K), X NO x is NO x conversion at different reaction temperatures, m cat is the weight of the sample, ω is the surface element content calculated by the XPS (%) (Table S1), and M represents the molar mass, respectively.…”

Constructing active copper species in Cu-zeolites for coal-gas-SCR and elucidating the synergistic catalytic function of CuO and Cu2+ ion species

“…The desorption peak located at 106 °C is attributed to the desorption of physically adsorbed NO. 51 The desorption peak at moderate temperature (∼272 °C) could be referred to the thermodynamically unstable nitrates formed by the adsorption of NO on Cu 2+ ions and the desorption peak at higher temperature (350–450 °C) could be attributed to the decomposition of nitrates with higher thermal stability. 51,52…”

“…The desorption peak located at 106 °C is attributed to the desorption of physically adsorbed NO. 51 The desorption Environmental Science: Nano Paper peak at moderate temperature (∼272 °C) could be referred to the thermodynamically unstable nitrates formed by the adsorption of NO on Cu 2+ ions and the desorption peak at higher temperature (350-450 °C) could be attributed to the decomposition of nitrates with higher thermal stability. 51,52 Note that more nitrates in Cu-ZSM-5-IE+CP decompose at 367 °C rather than at 379 °C for Cu-ZSM-5-IE or 414 °C for Cu-ZSM-5-CP, indicating that Cu-ZSM-5-IE+CP could generate more active nitrates which should react with coal gas readily.…”

Rapid solvent-free synthesis of nano-sized ZSM-5 with a low Si/Al ratio at 90 °C

“…ZSM-5 is a crystalline aluminosilicate zeolite with an MFI framework. [1][2][3] The unique pore structure and tuneable framework Si/Al ratio make the zeolite promising for its widespread use in petrochemical and fine chemical processes, such as catalytic-cracking, 4,5 catalytic-reforming, 6 selective catalytic reduction, 7 methanol to olefin (MTO), 8,9 and methanol to aromatics (MTA). 10 The hydrothermal method was first used to synthesize ZSM-5 by Argauer and Landolt, 11 and soon other synthetic methodologies, such as solvothermal and ionothermal routes, 12,13 were successively developed.…”