Journal ArticleDOI
Silver-alumina catalysts for selective reduction of NO by higher hydrocarbons: structure of active sites and reaction mechanism
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In this article, the selective catalytic reduction (SCR) of NO by higher alkanes (n-hexane and n-octane) was investigated by in situ FTIR spectroscopy.Abstract:
Silver-alumina catalysts prepared by sol–gel method (Ag-Al2O3) and impregnation method (Ag/Al2O3) were studied for the selective catalytic reduction (SCR) of NO by higher alkanes (n-hexane and n-octane). UV–VIS and Ag K-edge XAFS results established the structure of the catalysts; below 2 wt.%, highly dispersed Ag+ ions are predominant Ag species, while at higher Ag loading, Agn clusters are predominant. A relationship between the structure of Ag species and their catalytic function for SCR by n-octane was clarified. Ag+ ions are responsible for the selective reduction of NO to N2, while the Agn clusters are responsible for the hydrocarbon combustion and N2O formation. The mechanism of SCR by n-hexane on Ag-Al2O3, which mainly consists of Ag+ ions, were investigated by in situ FTIR spectroscopy. During NO+n-hexane+O2 reaction, the acetate produced via the partial oxidation of n-hexane and the nitrates produced via the oxidation of NO were main adspecies in the steady-state condition at 473–623 K. The acetate, which was stable in O2 or NO, was reactive in NO+O2. Nitrates, which were relatively stable in n-hexane, were quite reactive toward n-hexane+O2. The rate of nitrates reaction in n-hexane+O2 was close to the steady-state rate of NO reduction over wide range of temperature, indicating that the nitrate is a possible intermediate in the SCR. A proposed mechanism, suggesting the reaction of nitrates with partially oxidized hydrocarbon species as a crucial step, explains the steady-state kinetic results. At relatively high NO concentration or at low temperature, nitrates should inhibit the reaction by strongly adsorbing on the catalyst surface.read more
Citations
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A review of the selective reduction of NOx, with hydrocarbons under lean-burn conditions with non-zeolitic oxide and platinum group metal catalysts
TL;DR: In this paper, it is concluded that although there is indirect, mainly spectroscopic, evidence for various reaction intermediates on the catalyst surface, it is difficult to confirm that any of these are involved in a critical mechanistic step because of a lack of a direct quantitative correlation between infrared and kinetic measurements.
Journal ArticleDOI
Catalytic NOx Abatement Systems for Mobile Sources: From Three-Way to Lean Burn after-Treatment Technologies
TL;DR: Catalytic NOx Abatement Systems for Mobile Sources: From Three-Way to Lean Burn after-Treatment Technologies is presented.
Journal ArticleDOI
Plasmon-Induced Photodegradation of Toxic Pollutants with Ag−AgI/Al2O3 under Visible-Light Irradiation
TL;DR: A plasmonic photocatalyst supported on mesoporous alumina (Ag−AgI/Al2O3) was prepared by deposition−precipitation and photoreduction methods as mentioned in this paper.
Journal ArticleDOI
Knowledge and Know‐How in Emission Control for Mobile Applications
TL;DR: Early research on selective catalytic reduction on zeolite, oxide, and metal-based systems is examined, and some of the key mechanistic models are described as discussed by the authors. But none of these systems are of sufficient activity and stability to satisfy current legislation attention has turned to NO.
Journal ArticleDOI
Identification, Stability, and Reactivity of NOx Species Adsorbed on Titania-Supported Manganese Catalysts
TL;DR: In this paper, the properties of the NOx species obtained on NO adsorption and its coadsorption with O2 at room temperature on TiO2 and MnOx/TiO2 catalysts with two different manganese loadings have been studied by means of in situ Fourier transform infrared spectroscopy.
References
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A case study: surface chemistry and surface structure of catalytic aluminas, as studied by vibrational spectroscopy of adsorbed species
TL;DR: The main attention has been devoted to various aspects of the surface chemistry of aluminas, as revealed by the adsorption of selected probe molecules, rather than to a systematic description of the very many probe molecules used over the years.
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Mechanistic Aspects of the Selective Reduction of NO by Propene over Alumina and Silver–Alumina Catalysts
TL;DR: In this paper, the selective catalytic reduction of NO with C3H6 in the presence of a large excess of O2 was studied over γ-Al2O3 and the lowloading silver material exhibited high conversions to N2 whereas the highloading sample predominantly yielded N2O.
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Supported Ag Catalysts for the Lean Reduction of NO with C3H6
K. A. Bethke,Harold H. Kung +1 more
TL;DR: In this article, the activities of 2 and 6 wt% Ag/Al2O3 catalysts for lean NO reduction with C3H6 were compared, and the difference in the behavior of the two catalysts was attributed to the much higher Ag dispersion for the 2 wt % than the 6 Wt % sample, such that the oxidation states of Ag were different under reaction conditions.
Journal ArticleDOI
Selective reduction of nitrogen oxides by hydrocarbons under lean-burn conditions using supported platinum group metal catalysts
Robert Burch,P.J. Millington +1 more
TL;DR: In this article, the performance of supported platinum-group metals (Pt, Pd, Rh, Ir and Ru) for the selective reduction of nitrogen oxides by hydrocarbons under oxidising conditions is reviewed.