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Author: Mark Crocker Publisher: ISBN: Category : Languages : en Pages :
Book Description
This study was undertaken in order to assess the potential for oxidizing NO to NO{sub 2} in flue gas environments, with the aim of promoting the so-called fast SCR reaction. In principle this can result in improved SCR kinetics and reduced SCR catalyst volumes. Prior to commencing experimental work, a literature study was undertaken to identify candidate catalysts for screening. Selection criteria comprised (1) proven (or likely) activity for NO oxidation, (2) low activity for SO2 oxidation (where data were available), and (3) inexpensive component materials. Catalysts identified included supported base metal oxides, supported and unsupported mixed metal oxides, and metal ion exchanged ZSM-5 (Fe, Co, Cu). For comparison purposes, several low loaded Pt catalysts (0.5 wt% Pt) were also included in the study. Screening experiments were conducted using a synthetic feed gas representative of flue gas from coal-fired utility boilers: [NO] = 250 ppm, [SO{sub 2}] = 0 or 2800 ppm, [H{sub 2}O] = 7%, [CO{sub 2}] = 12%, [O{sub 2}] = 3.5%, balance = N{sub 2}; T = 275-375 C. Studies conducted in the absence of SO{sub 2} revealed a number of supported and unsupported metal oxides to be extremely active for NO oxidation to NO{sub 2}. These included known catalysts (Co{sub 3}O{sub 4}/SiO{sub 2}, FeMnO{sub 3}, Cr{sub 2}O{sub 3}/TiO{sub 2}), as well as a new one identified in this work, CrFeO{sub x}/SiO{sub 2}. However, in the presence of SO{sub 2}, all the catalysts tested were found to be severely deactivated with respect to NO oxidation. Of these, Co{sub 3}O{sub 4}/SiO{sub 2}, Pt/ZSM-5 and Pt/CeO{sub 2} showed the highest activity for NO oxidation in the presence of SO{sub 2} (based on peak NO conversions to NO{sub 2}), although in no cases did the NO conversion exceed 7%. Reactor studies indicate there are two components to SO{sub 2}-induced deactivation of Co{sub 3}O{sub 4}/SiO{sub 2}, corresponding to an irreversible deactivation due to sulfation of the surface of the Co{sub 3}O{sub 4} phase, together with a reversible inhibition due to competitive adsorption of SO{sub 2} with NO on the catalyst. In an effort to minimize the deactivating effect of SO{sub 2} on Co{sub 3}O{sub 4}/SiO{sub 2}, two synthetic approaches were briefly examined. These consisted of (1) the incorporation of highly dispersed Co(II) ions in silica, as a non-sulfating matrix, via the sol-gel preparation of CoO-SiO{sub 2}; and (2) the sol-gel preparation of a mixed metal oxide, CoO-Nb{sub 2}O{sub 5}-SiO{sub 2}, with the aim of exploiting the acidity of the niobium oxide to minimize SO2 adsorption. While both catalysts showed almost no activity for NO oxidation in the absence of SO{sub 2}, when SO{sub 2} was present low activity was observed, indicating that SO{sub 2} acts as a promoter for NO oxidation over these materials. The kinetics of NO oxidation over Co{sub 3}O{sub 4}/SiO{sub 2}, Pt/SiO{sub 2} and Pt/CeO{sub 2} were also examined. Co{sub 3}O{sub 4}/SiO{sub 2} was found to exhibit a higher apparent activation energy for NO oxidation than the Pt catalysts, while the combined reaction order in NO and O{sub 2} for the three catalysts was very close to one. CO{sub 2} was found to have no effect on the kinetics of NO oxidation over these catalysts. The presence of H{sub 2}O caused a decrease in NO conversion for both Co{sub 3}O{sub 4}/SiO{sub 2} and Pt/CeO{sub 2} catalysts, while no effect was observed for Pt/SiO{sub 2}. The inhibiting effect of water was reversible and is attributed to competitive adsorption with the reactants. In sum, this study has shown that a variety of base metal catalysts are very active for NO oxidation. However, all of the catalysts studied are strongly deactivated in the presence of 2800 ppm SO{sub 2} at typical flue gas temperatures; consequently improving catalyst resistance to SO{sub x} will be a pre-requisite if the fast SCR concept is to be applied to coal-fired flue gas conditions.
Author: Mark Crocker Publisher: ISBN: Category : Languages : en Pages :
Book Description
This study was undertaken in order to assess the potential for oxidizing NO to NO{sub 2} in flue gas environments, with the aim of promoting the so-called fast SCR reaction. In principle this can result in improved SCR kinetics and reduced SCR catalyst volumes. Prior to commencing experimental work, a literature study was undertaken to identify candidate catalysts for screening. Selection criteria comprised (1) proven (or likely) activity for NO oxidation, (2) low activity for SO2 oxidation (where data were available), and (3) inexpensive component materials. Catalysts identified included supported base metal oxides, supported and unsupported mixed metal oxides, and metal ion exchanged ZSM-5 (Fe, Co, Cu). For comparison purposes, several low loaded Pt catalysts (0.5 wt% Pt) were also included in the study. Screening experiments were conducted using a synthetic feed gas representative of flue gas from coal-fired utility boilers: [NO] = 250 ppm, [SO{sub 2}] = 0 or 2800 ppm, [H{sub 2}O] = 7%, [CO{sub 2}] = 12%, [O{sub 2}] = 3.5%, balance = N{sub 2}; T = 275-375 C. Studies conducted in the absence of SO{sub 2} revealed a number of supported and unsupported metal oxides to be extremely active for NO oxidation to NO{sub 2}. These included known catalysts (Co{sub 3}O{sub 4}/SiO{sub 2}, FeMnO{sub 3}, Cr{sub 2}O{sub 3}/TiO{sub 2}), as well as a new one identified in this work, CrFeO{sub x}/SiO{sub 2}. However, in the presence of SO{sub 2}, all the catalysts tested were found to be severely deactivated with respect to NO oxidation. Of these, Co{sub 3}O{sub 4}/SiO{sub 2}, Pt/ZSM-5 and Pt/CeO{sub 2} showed the highest activity for NO oxidation in the presence of SO{sub 2} (based on peak NO conversions to NO{sub 2}), although in no cases did the NO conversion exceed 7%. Reactor studies indicate there are two components to SO{sub 2}-induced deactivation of Co{sub 3}O{sub 4}/SiO{sub 2}, corresponding to an irreversible deactivation due to sulfation of the surface of the Co{sub 3}O{sub 4} phase, together with a reversible inhibition due to competitive adsorption of SO{sub 2} with NO on the catalyst. In an effort to minimize the deactivating effect of SO{sub 2} on Co{sub 3}O{sub 4}/SiO{sub 2}, two synthetic approaches were briefly examined. These consisted of (1) the incorporation of highly dispersed Co(II) ions in silica, as a non-sulfating matrix, via the sol-gel preparation of CoO-SiO{sub 2}; and (2) the sol-gel preparation of a mixed metal oxide, CoO-Nb{sub 2}O{sub 5}-SiO{sub 2}, with the aim of exploiting the acidity of the niobium oxide to minimize SO2 adsorption. While both catalysts showed almost no activity for NO oxidation in the absence of SO{sub 2}, when SO{sub 2} was present low activity was observed, indicating that SO{sub 2} acts as a promoter for NO oxidation over these materials. The kinetics of NO oxidation over Co{sub 3}O{sub 4}/SiO{sub 2}, Pt/SiO{sub 2} and Pt/CeO{sub 2} were also examined. Co{sub 3}O{sub 4}/SiO{sub 2} was found to exhibit a higher apparent activation energy for NO oxidation than the Pt catalysts, while the combined reaction order in NO and O{sub 2} for the three catalysts was very close to one. CO{sub 2} was found to have no effect on the kinetics of NO oxidation over these catalysts. The presence of H{sub 2}O caused a decrease in NO conversion for both Co{sub 3}O{sub 4}/SiO{sub 2} and Pt/CeO{sub 2} catalysts, while no effect was observed for Pt/SiO{sub 2}. The inhibiting effect of water was reversible and is attributed to competitive adsorption with the reactants. In sum, this study has shown that a variety of base metal catalysts are very active for NO oxidation. However, all of the catalysts studied are strongly deactivated in the presence of 2800 ppm SO{sub 2} at typical flue gas temperatures; consequently improving catalyst resistance to SO{sub x} will be a pre-requisite if the fast SCR concept is to be applied to coal-fired flue gas conditions.
Author: Publisher: ISBN: Category : Languages : en Pages : 77
Book Description
The most advanced and proven technology for NO(subscript x) control for stationary sources is Selective Catalytic Reduction (SCR). In SCR, NO(subscript x) is reduced by NH3 to N2 and H2O. The commercial catalysts are based on V2O5/TiO2, and the vanadium-based catalysts are patented by the Japanese (Mitsubishi). However, there are three main advantages for the vanadium-based SCR catalyst: (a) a tendency to be poisoned in the flue gas; (b) oxidation of SO2 to SO3 by V2O5, this is a particularly severe problem due to the higher sulfur content of American coals compared with coals used in Japan (from Australia) and in Europe; (c) environmental problems involved in the disposal of the spent catalyst (due to the toxicity of vanadium). In order to overcome these problems, in addition to the undesirable dominance by the Japanese patent position, the authors have studied in this project a new type of catalyst for the SCR reaction; namely, pillared clays, which have adjustable, unique structures and acidity. Three types of catalysts were developed and tested for this reaction, i.e. Fe2O3-pillared clays, delaminated Fe2O3-pillared clays, and ion-exchanged pillared clays. The project was divided into sixteen tasks, and will be reported as such.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
Seven first row transition metals were deposited on various commercial TiO2, SiO2, and Al2 O3 supports to create mono- and bimetallic catalysts that were compared in the selective catalytic reduction of nitric oxide using ammonia at low temperatures ranging from 373-523 K. The catalyst with the highest activity both in the absence and presence of water in the feed was 20 wt.% Mn/Hombikat TiO2 synthesized from a nitrate precursor and calcined below 673 K. Under those conditions, it was capable of achieving 100% NO conversion at 393 K. Numerous surface characterization techniques were used to identify the surface properties that result in highly active and selective low temperature SCR catalysts. The deposition of manganese as MnO2, the ease of reducibility of the metal oxide, and the symmetric deformation of ammonia coordinated to Lewis acid sites at 1167 cm−1, were all found to be important for good catalytic performance. No synergistic effects were observed from combinations of the three most active transition metals. However, MnO x -NiO/TiO2 had an extended lifetime relative to MnO x /TiO2 in feeds containing SO2 . The extensive data collected from in-situ FTIR experiments in the presence of NO and NH 3 were used to propose a reaction mechanism for MnO x /TiO2 that begins with the coordination of NH3 over Mn4 species and proceeds through the formation of bridged nitrates. A combination of potentiometric titrations and UV/Vis spectroscopy were used to quantify the reduction of V5 to V4 after the addition of oxalic acid as the solution is aged. After approximately four hours, the aging vanadium oxalate solution reaches steady state, and the final distribution of the vanadium present is 89% V+4 and 11% V+5 . TiO2 supported monolayer catalysts synthesized from the aged (V+4) vanadium oxalate solution consistently outperformed catalysts made from freshly prepared (V+5) vanadium oxalate solutions. Surface characterization revealed that surface acid sites increase in strength and vanadia reduces more easily in catalysts synthesized from aged vanadium oxalate solutions, which enhances reaction mechanism depends upon acid sites and redox operation.
Author: Hyuk Jin Oh Publisher: ISBN: Category : Languages : en Pages :
Book Description
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.
Author: Publisher: ISBN: Category : Languages : en Pages : 14
Book Description
Significant work has been done by the investigators on the cerium oxide-copper oxide based sorbent/catalysts for the combined removal of sulfur and nitrogen oxides from the flue gases of stationary sources. A relatively wide temperature window was established for the use of alumina-supported cerium oxide-copper oxide mixtures as regenerable sorbents for SO2 removal. Evaluation of these sorbents as catalysts for the selective reduction of NO(subscript x) gave promising results with methane. Since the replacement of ammonia by methane is commercially very attractive, in this project, it was planned to investigate the effect of promoters on the activity and selectivity of copper oxide/cerium oxide-based catalysts and to obtain data on the reaction mechanism for the SCR with methane. The investigation of the reaction mechanism will help in the selection of promoters to improve the catalytic activity and selectivity of the sorbents in the SCR with methane. This will result in new catalyst formulations. The last component of the project involves our industrial partner TDA Research, and the objective is to evaluate long- term stability and durability of the prepared sorbent/catalysts. In the second year of the project, the catalysts were investigated for their SCR activity with methane in a microreactor setup and also, by the temperature-programmed desorption (TPD) technique. The results from the SCR experiments indicated that manganese is a more effective promoter than rhodium on the supported copper oxide-ceria catalysts under study; the effectiveness of the promoter increases with the increase in Ce/Cu ratio. The TPD profiles of the unpromoted catalyst (Cu/Ce=3) is different than those promoted with 0.1% rhodium. In the current reporting period, the screening of the promoted catalysts were completed, sufficient amount of the selected catalysts were prepared and delivered to TDA for long term deactivation testing.
Author: Philippe Arpentinier Publisher: Editions Technip ISBN: 9782710807773 Category : Science Languages : en Pages : 378
Book Description
Volume 1 covers the most important technological aspects of the use of molecular oxygen for catalytic oxidation reactions.Volume 2 addresses the safety issues associated with the use of oxygen in catalytic oxidation reactions.Contents Vol. 1: 1. Introduction. 2. Chemical-physical properties of molecular oxygen. 3. Oxygen production technologies. 4. Chemical fundamentals of oxidation reactions. 5. Reactor technologies for multiphase systems. 6. Liquid phase oxidations. 7. Gas phase selective oxidations. 8. Selective oxidation of paraffins. References. Index. Vol. 2: 9. Introduction to safety problems in the chemical industry. 10. Chemical aspects of combustion in the gaseous phase. 11. Homogeneous chemical explosions: autoignition or spontaneous ignition. 12. Deflagration or propagation of flame. 13. Conditions governing flame propagation capability. 14. Detonation in the gaseous phase. 15. Prevention of and protection against explosions. References. Index.
Author: Mark Crocker
Author: Mark Crocker
Author: 
Author: 
Author: Ralph William Baker
Author: Hyuk Jin Oh
Author: Hung-Ning Wong
Author: Curtis N. Eng
Author: 
Author: Oliver Kröcher
Author: Philippe Arpentinier