The open literature concerning chemical and mechanistic aspects of the selective catalytic reduction of NO by ammonia (SCR process) on metal oxide catalysts is reviewed. Catalytic systems based on supported V2O5 (including the industrial TiO2-supported V2O5–WO3 and/or V2O5–MoO3 catalysts) and catalysts containing Fe2O3, CuO, MnOx and CrOx are considered. The results of spectroscopic studies of the adsorbed surface species, adsorption–desorption measurements, flow reactor and kinetic experiments are analyzed. The proposed reaction mechanisms are described and critically discussed. Points of convergence and of disagreement are underlined.

Chemical and mechanistic aspects of the selective catalytic reduction of NOx by ammonia over oxide catalysts: A review

Catalytic removal of NO

An overview is given of the selective catalytic reduction of NOx by ammonia (NH3‐SCR) over metal‐exchanged zeolites. The review gives a comprehensive overview of NH3‐SCR chemistry, including undesired side‐reactions and aspects of the reaction mechanism over zeolites and the active sites involved. The review attempts to correlate catalyst activity and stability with the preparation method, the exchange metal, the exchange degree, and the zeolite topology. A comparison of Fe‐ZSM‐5 catalysts prepared by different methods and research groups shows that the preparation method is not a decisive factor in determining catalytic activity. It seems that decreased turnover frequency (TOF) is an oft‐neglected effect of increasing Fe content, and this oversight may have led to the mistaken conclusion that certain production methods produce highly active catalysts. The available data indicate that both isolated and bridged iron species participate in the NH3‐SCR reaction over Fe‐ZSM‐5, with isolated species being the ...

https://www.tandfonline.com/doi/pdf/10.1080/01614940802480122

The State of the Art in Selective Catalytic Reduction of NOx by Ammonia Using Metal‐Exchanged Zeolite Catalysts

A series of high-activity manganese−cerium oxide catalysts for the low-temperature (373−453 K) selective catalytic reduction (SCR) of NOx with ammonia were prepared. They were prepared by using the...

Characterization and FTIR Studies of MnOx−CeO2 Catalyst for Low-Temperature Selective Catalytic Reduction of NO with NH3

Mechanism of the Selective Catalytic Reduction of NO by NH3over MnOx/Al2O3☆

Investigation of the Reaction Pathways in Selective Catalytic Reduction of NO with NH3 over V2O5 Catalysts: Isotopic Labeling Studies Using 18O2, 15NH3, 15NO, and 15N18O

Investigation of the mechanism of ammonia oxidation and oxygen exchange over vanadia catalysts using N-15 and O-18 tracer studies

Self-Sustained Oscillatory Behavior of NO+CH4+O2Reaction over Titania-Supported Pd Catalysts

Characterization and temperature-programmed studies over Pd/TiO2 catalysts for NO reduction with methane

Structural specificity of vanadium pentoxide catalysts was investigated in the selective catalytic reduction (SCR) of nitric oxide. Catalysts were prepared by different temperature-programmed methods to obtain particles having preferential exposure of different crystal planes. Catalyst samples were characterized using the BET surface area technique, X-ray diffraction, laser Raman spectroscopy. X-ray photoelectron spectroscopy, scanning electron microscopy and 3-D imaging techniques. A steady-state fixed-bed reactor system was used for activity and selectivity measurements. Identification and quantification of reaction effluents were achieved using an analytical scheme that combined gas chromatography, chemiluminescence, gas chromatography-mass spectroscopy and wet chemistry techniques. Samples that preferentially exposed the (010) basal planes were found to promote direct oxidation of ammonia more readily than nitric oxide reduction as evidenced by the differences in nitric oxide and ammonia conversions and in nitrogen and nitrous oxide yields. The difference in catalytic activity and selectivity was related to the relative abundance of V O sites exposed on the catalyst surface and the competing reactions that are involved in SCR and direct ammonia oxidation reaction schemes.

M. W. Kumthekar

Papers

Investigation of the Reaction Pathways in Selective Catalytic Reduction of NO with NH3 over V2O5 Catalysts: Isotopic Labeling Studies Using 18O2, 15NH3, 15NO, and 15N18O

Investigation of the mechanism of ammonia oxidation and oxygen exchange over vanadia catalysts using N-15 and O-18 tracer studies

Self-Sustained Oscillatory Behavior of NO+CH4+O2Reaction over Titania-Supported Pd Catalysts

Characterization and temperature-programmed studies over Pd/TiO2 catalysts for NO reduction with methane

Effect of crystal morphology in selective catalytic reduction of nitric oxide over V2O5 catalysts