Selective Catalytic Reduction of NO by NH3 with WO3-TiO2 Catalysts PDF Download
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Languages : en
Pages : 11
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A series of supported WO3/TiO2 catalysts was prepared by a new synthesis procedure involving co-precipitation of an aqueous TiO(OH)2 and (NH4)10W12O41*5H2O slurry under controlled pH conditions. The morphological properties, molecular structures, surface acidity and surface chemistry of the supported WO3/TiO2 catalysts were determined with BET, in situ Raman, in situ IR and temperature-programmed surface reaction (TPSR) spectroscopy, respectively. Isotopic 18O-16O exchange demonstrated that tungsten oxide was exclusively present as surface WOx species on the TiO2 support with mono-oxo W=O coordination. In contrast to previous studies employing impregnation synthesis that found only surface one mono-oxo O=WO4 site on TiO2, the co-precipitation procedure resulted in the formation of two distinct surface WOx species: mono-oxo O=WO4 (~1010-1017 cm-1) on low defect density patches of TiO2 and a second mono-oxo O=WO4 (~983-986 cm-1) on high defect density patches of TiO2. The concentration of the second WOx surface species increases as a function of solution pH. Both surface WOx sites, however, exhibited the same NO/NH3 SCR reactivity. The co-precipitated WO3-TiO2 catalysts synthesized in alkaline solutions exhibited enhanced performance for the NO/NH3 SCR reaction that is ascribed to the greater number of surface defects on the resulting TiO2 support. For the co-precipitated catalyst prepared at pH10, surface NH4+ species on Br nsted acid sites were found to be more reactive than surface NH3* species on Lewis acid sites for SCR of NO with NH3.
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Category :
Languages : en
Pages : 11
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Book Description
A series of supported WO3/TiO2 catalysts was prepared by a new synthesis procedure involving co-precipitation of an aqueous TiO(OH)2 and (NH4)10W12O41*5H2O slurry under controlled pH conditions. The morphological properties, molecular structures, surface acidity and surface chemistry of the supported WO3/TiO2 catalysts were determined with BET, in situ Raman, in situ IR and temperature-programmed surface reaction (TPSR) spectroscopy, respectively. Isotopic 18O-16O exchange demonstrated that tungsten oxide was exclusively present as surface WOx species on the TiO2 support with mono-oxo W=O coordination. In contrast to previous studies employing impregnation synthesis that found only surface one mono-oxo O=WO4 site on TiO2, the co-precipitation procedure resulted in the formation of two distinct surface WOx species: mono-oxo O=WO4 (~1010-1017 cm-1) on low defect density patches of TiO2 and a second mono-oxo O=WO4 (~983-986 cm-1) on high defect density patches of TiO2. The concentration of the second WOx surface species increases as a function of solution pH. Both surface WOx sites, however, exhibited the same NO/NH3 SCR reactivity. The co-precipitated WO3-TiO2 catalysts synthesized in alkaline solutions exhibited enhanced performance for the NO/NH3 SCR reaction that is ascribed to the greater number of surface defects on the resulting TiO2 support. For the co-precipitated catalyst prepared at pH10, surface NH4+ species on Br nsted acid sites were found to be more reactive than surface NH3* species on Lewis acid sites for SCR of NO with NH3.
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Category : Ammonia
Languages : en
Pages : 174
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Author: Oliver Kröcher
Publisher: MDPI
ISBN: 3038973645
Category : Science
Languages : en
Pages : 281
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This book is a printed edition of the Special Issue "Selective Catalytic Reduction of NO
x" that was published in Catalysts
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Category :
Languages : en
Pages : 10
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We compared the molecular structures, surface acidity and catalytic activity for NO/NH3/O2 SCR of V2O5-WO3/TiO2 catalysts for two different synthesis methods: co-precipitation of aqueous vanadium and tungsten oxide precursors with TiO(OH)2 and by incipient wetness impregnation of the aqueous precursors on a reference crystalline TiO2 support (P25; primarily anatase phase). Bulk analysis by XRD showed that co-precipitation results in small and/or poorly ordered TiO2(anatase) particles and that VOx and WOx do not form solid solutions with the bulk titania lattice. Surface analysis of the co-precipitated catalyst by High Sensitivity-Low Energy Ion Scattering (HS-LEIS) confirms that the VOx and WOx are surface segregated for the co-precipitated catalysts. In situ Raman and IR spectroscopy revealed that the vanadium and tungsten oxide components are present as surface mono-oxo O = VO3 and O = WO4 sites on the TiO2 supports. Co-precipitation was shown for the first time to also form new mono-oxo surface VO4 and WO4 sites that appear to be anchored at surface defects of the TiO2 support. IR analysis of chemisorbed ammonia showed the presence of both surface NH3* on Lewis acid sites and surface NH4+* on Brønsted acid sites. TPSR spectroscopy demonstrated that the specific SCR kinetics was controlled by the redox surface VO4 species and that the surface kinetics was independent of TiO2 synthesis method or presence of surface WO5 sites. SCR reaction studies revealed that the surface WO5 sites possess minimal activity below ~325 °C and their primary function is to increase the adsorption capacity of ammonia. A relationship between the SCR activity and surface acidity was not found. The SCR reaction is controlled by the surface VO4 sites that initiate the reaction at ~200 °C. The co-precipitated catalysts were always more active than the corresponding impregnated catalysts. Finally, we ascribe the higher activity of the co-precipitated catalysts to the presence of the new surface WOx sites associated surface defects on the TiO2 support that increase the ammonia adsorption capacity.
Author: Archareeyaporn Ruengthawornkul
Publisher:
ISBN:
Category : Catalysts
Languages : en
Pages : 158
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The present work investigates the formation of N2O during the SCR of NO with NH3 over V2O5/TiO2, WO3/TiO2, MoO3/TiO2, V2O5-WO3/TiO2 and V2O5-MoO3/TiO2 catalysts. All catalysts are characterized by using BET surface area measurement, XRD, FT-IR, NH3-TPD, Pyridine adsorption, and ICP-OES. The effluent gas in the SCR experimental contains 120 ppm NO, 120 ppm NH3, 30 ppm SO2, 15 vol% O2, and 15 vol% H2O, balanced with N2. The reaction is carried out in the reaction temperature 120-450°C. A gas chromatograph Shimadzu GC-2014 equipped with an ECD is used to measure the amount of NO and N2O in the effluent gas. The effect of SO2 on the formation of N2O during the SCR process over the catalysts is tested by removing SO2 from the feed gas. The effect of O2 on the formation of N2O during the SCR process over the catalysts is tested by removing O2 from the feed gas. The results show that O2 is necessary for the SCR of NO by NH3 over WO3/TiO2 and V2O5-WO3/TiO2 catalysts. The SCR of NO over V2O5/TiO2, MoO3/TiO2 and V2O5-MoO3/TiO2 catalysts can proceed in the absence of O2, but at a higher reaction temperature with a large amount of N2O form. The results demonstrate that lattice oxygen (O-2) of V2O5/TiO2, MoO3/TiO2 and V2O5-MoO3/TiO2 catalysts can participate the SCR process at the high reaction temperature. O-2 on MoO3/TiO2 and V2O5-MoO3/TiO2 catalysts is participate to increase N2O formed from the SCR process. N2O is formed from the reaction between NH3 and O2 rather than NO.
Author: Thomas Rammelt
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Languages : de
Pages :
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Author: Thomas Rammelt
Publisher:
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Category :
Languages : en
Pages :
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Author: Hyuk Jin Oh
Publisher:
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Category :
Languages : en
Pages :
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The selective catalytic reduction (SCR) of nitric oxide (NO) with ammonia over vanadia-based (V2O5-WO3/TiO2) and pillared interlayer clay-based (V2O5/Ti-PILC) monolithic honeycomb catalysts using a laboratory laminar-flow reactor was investigated. The experiments used a number of gas compositions to simulate different combustion gases. A Fourier transform infrared (FTIR) spectrometer was used to determine the concentrations of the product species. The major products were nitric oxide (NO), ammonia (NH3), nitrous oxide (N2O), and nitrogen dioxide (NO2). The aim was to delineate the effect of various parameters including reaction temperature, oxygen concentration, NH3-to-NO ratio, space velocity, heating area, catalyst arrangement, and vanadium coating on the removal of nitric oxide. The investigation showed that the change of the parameters significantly affected the removals of NO and NH3 species, the residual NH3 concentration (or NH3 slip), the temperature of the maximum NO reduction, and the temperature of complete NH3 conversion. The reaction temperature was increased from the ambient temperature (25°C) to 450°C. For both catalysts, high NO and NH3 removals were obtained in the presence of a small amount of oxygen, but no significant influence was observed from 0.1 to 3.0% O2. An increase in NH3-to-NO ratio increased NO reduction but decreased NH3 conversions. For V2O5-WO3/TiO2, the decrease of space velocity increased NO and NH3 removals and broadened the active temperature window (based on NO> 88% and NH3> 87%) about 50°C. An increase in heating area decreased the reaction temperature of the maximum NO reduction from 350 to 300 ʻC, and caused the active reaction temperature window (between 250 and 400 ʻC) to shift toward 50 ʻC lower reaction temperatures (between 200 and 350°C). The change of catalyst arrangements resulted slight improvement for NO and NH3 removals, therefore, the change might contribute to more gas removals. The catalyst with extra vanadium coating showed higher NO reductions and NH3 conversions than the catalyst without the extra vanadium coating.
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Category : Ammonia
Languages : en
Pages : 166
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Author:
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ISBN:
Category :
Languages : en
Pages : 37
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A delaminated Fe2O3-pillared clay catalyst was prepared for the selective catalytic reduction (SCR) of NO by NH3 at above 300°C. The delaminated pillard clay was characterized by ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectroscopy) chemical analysis, XRD (X-ray diffraction) structure and line broadening analyses, micropore size probing, and Moessbauer analysis. These analyses showed that the catalyst contained fragmented Fe2O3-pillared clay forming {open_quotes}house-of-cards{close_quotes} structure with dispersed Fe2O3 particles approximately 170 Å in size. The SCR activity of the delaminated pillard clay was higher than the commercial-type V2O5 + WO3/TiO2 catalyst, and also higher than the undelaminated pillard clay and supported Fe2O3 catalysts, under conditions with SO2. Infrared measurements of adsorbed NH3 showed strong Bronsted acidity which was caused possibly by interactions between Fe2O3 and clay.
