Selective catalytic reduction

About: Selective catalytic reduction is a research topic. Over the lifetime, 10502 publications have been published within this topic receiving 226291 citations.

Mechanistic Aspects of the H2-SCR of NO on a Novel Pt/MgO−CeO2 Catalyst

Abstract: Steady State Isotopic Transient Kinetic Analysis (SSITKA) coupled with Temperature-Programmed Surface Reaction (TPSR) experiments, using on line Mass Spectroscopy (MS) and in situ DRIFTS have been performed to study essential mechanistic aspects of the selective catalytic reduction of NO by H2 under strongly oxidizing conditions (H2-SCR) at 140 °C over a novel 0.1 wt % Pt/MgO−CeO2 catalyst for which patents have been recently obtained. The nitrogen paths of reaction from NO to N2 and N2O gas products were probed by following the 14NO/H2/O2 → 15NO/H2/O2 switch (SSITKA-MS and SSITKA-DRIFTS) at 1 bar total pressure. It was found that the N-pathways of reaction involve two different in structure active chemisorbed NOx species, one present on the MgO and the other one on the CeO2 support surface. The amount of these active NOx intermediate species formed was found to be 14.4 μmol/g, corresponding to a surface coverage of θ = 3.1 (based on Pt metal surface) in agreement with the SSITKA-DRIFTS results. A large f...

H2O and SO2 deactivation mechanism of MnOx/MWCNTs for low-temperature SCR of NOx with NH3

Abstract: The effect of H 2 O and SO 2 on the catalytic activity of manganese oxides supported on multi-walled carbon nanotubes (MnO x /MWCNTs) for low-temperature selective catalytic reduction (SCR) of NO x with NH 3 was studied. Also, N 2 adsorption, transient response experiments, X-ray powder diffraction (XRD), Raman spectroscopy, Fourier transform infrared (FT-IR) spectroscopy and in situ FT-IR spectroscopy were performed to investigate the deactivation mechanism of MnO x /MWCNTs catalyst in the presence of H 2 O or SO 2 . Experimental results showed that H 2 O had a reversible negative effect on the catalytic activity of the catalyst. When the temperature was higher than 270 °C, the effect of H 2 O could be negligible. The competitive adsorption of H 2 O and NH 3 on the Lewis acid sites contributed to the deactivation of the catalyst. The integrity increase of MWCNTs in the presence of H 2 O might be another reason for the deactivation of the catalyst. However, SO 2 led to the irreversible deactivation of the catalyst. The higher the reaction temperature, the more dramatically the catalystic activity decreased. The sulfation of the active center atoms was the main poisoning route. Also, formation of ammonium sulfates on the catalyst surface and the competitive adsorption between SO 2 and NO were responsible for the partial deactivation of the catalyst to some extent.

Homogeneous Photocatalytic Reduction of CO2 to CO Using Iron(0) Porphyrin Catalysts: Mechanism and Intrinsic Limitations

Abstract: A photochemical catalytic reduction of CO2 was performed in an organic solvent with iron(0) porphyrins as homogeneous molecular catalysts under visible light irradiation. With modified tetraphenylporphyrins consisting of internal phenolic groups, the photochemical process led to the production of CO, with H2 as a minor product. High catalytic selectivity for CO formation and turnover numbers up to 30 were obtained. Degradation of the catalyst occurred at longer irradiation times, along with decreased selectivity. Furthermore, addition of a weak acid, which increased the reduction efficiency under electrochemical conditions, led to rapid deactivation of the catalyst. With the unmodified tetraphenylporphyrin as catalyst, we observed lower performance and higher proportion of H2, which highlighted differences in the reduction pathways followed. A combination of a spectroscopic study and product analysis performed under various conditions led to detailed reduction mechanisms and helped pave the way for designing durable photocatalytic systems.

Intermediates in the Selective Reduction of NO by Propene over Cu−Al2O3 Catalysts: Transient in−Situ FTIR Study

Abstract: The mechanism of the selective catalytic reduction (SCR) of NO by C3H6 on Cu−Al2O3 catalysts, which consist of highly dispersed Cu2+ ions in the surface aluminate phase, are investigated by in-situ FTIR spectroscopy. During NO + C3H6 + O2 reaction, the acetate is produced via the partial oxidation of C3H6 and becomes the predominant adspecies in the steady-state condition at 473−623 K. The acetate, which is stable in NO, is quite reactive with NO + O2, leading to the formation of isocyanate species (Cu−NCO) on the surface and N2 and CO2 in the gas phase. The rate of acetate reaction in NO + O2 is close to the steady-state rate of NO reduction over wide range of temperature, indicating that the acetate is an intermediate in the SCR and takes part in the rate-determining stage. A mechanism is proposed; the acetate and nitrates, formed by NO + O2, react to generate the Cu−NCO species, then Cu−NCO reacts with nitrates or NO to produce N2 and CO2. This mechanism explains the role of oxygen in facilitating SCR....