共查询到20条相似文献,搜索用时 598 毫秒
1.
Yuanjing Zheng Anker Degn Jensen Jan Erik Johnsson Joakim Reimer Thgersen 《Applied catalysis. B, Environmental》2008,83(3-4):186-194
In this work, deactivation of a commercial type V2O5-WO3-TiO2 catalyst by aerosols of potassium compounds was investigated in two ways: (1) by exposing the catalyst in a lab-scale reactor to a layer of KCl particles or fly ash from biomass combustion; (2) by exposing full-length monolith catalysts to pure KCl or K2SO4 aerosols in a bench-scale reactor. Exposed samples were characterized by activity measurements, SEM-EDX, BET/Hg-porosimetry, and NH3 chemisorption. The work was carried out to support the interpretation of observations of a previous study in which catalysts were exposed on a full-scale biomass fired power plant and to reveal the mechanisms of catalyst deactivation.Slight deactivation (about 10%) was observed for catalyst plates exposed to a layer of KCl particles at 350 °C for 2397 h. No deactivation was found for catalyst plates exposed for 2970 h to fly ash (consisting mainly of KCl and K2SO4) collected from an SCR pilot plant installed on a straw-fired power plant. A fast deactivation was observed for catalysts exposed to pure KCl or K2SO4 aerosols at 350 °C in the bench-scale reactor. The deactivation rates for KCl aerosol and K2SO4 aerosol exposed catalysts were about 1% per day and 0.4% per day, respectively.SEM analysis of potassium-containing aerosol exposed catalysts revealed that the potassium salt partly deposited on the catalyst outer wall which may decrease the diffusion rate of NO and NH3 into the catalyst. However, potassium also penetrated into the catalyst wall and the average K/V ratios (0.5–0.75) in the catalyst structure are high enough to explain the level of deactivation observed. The catalyst capacity for NH3 chemisorption decreased as a function of exposure time, which reveals that Brønsted acid sites had reacted with potassium compounds and thereby rendered inactive in the catalytic cycle. The conclusion is that chemical poisoning of active sites is the dominating deactivation mechanism, but physical blocking of the surface area may also contribute to the loss of activity in a practical application. The results support the observation and mechanisms of deactivation of SCR catalysts in biomass fired systems proposed in a previous study [Y. Zheng, A.D. Jensen, J.E. Johnsson, Appl. Catal. B 60 (2005) 253]. 相似文献
2.
Yinghua Chen Yanming Zhao Xiaoning An Jianmin Liu Youzhong Dong Ling Chen 《Electrochimica acta》2009,54(24):5844-5850
Cr-doped Li3V2−xCrx(PO4)3/C (x = 0, 0.05, 0.1, 0.2, 0.5, 1) compounds have been prepared using sol–gel method. The Rietveld refinement results indicate that single-phase Li3V2−xCrx(PO4)3/C with monoclinic structure can be obtained. Although the initial specific capacity decreased with Cr content at a lower current rate, both cycle performance and rate capability have excited improvement with moderate Cr-doping content in Li3V2−xCrx(PO4)3/C. Li3V1.9Cr0.1(PO4)3/C compound presents an initial capacity of 171.4 mAh g−1 and 78.6% capacity retention after 100 cycles at 0.2C rate. At 4C rate, the Li3V1.9Cr0.1(PO4)3/C can give an initial capacity of 130.2 mAh g−1 and 10.8% capacity loss after 100 cycles where the Li3V2(PO4)3/C presents the initial capacity of 127.4 mAh g−1 and capacity loss of 14.9%. Enhanced rate and cyclic capability may be attributed to the optimizing particle size, carbon coating quality, and structural stability during the proper amount of Cr-doping (x = 0.1) in V sites. 相似文献
3.
The deactivation of a commercial Selective Catalytic Reduction (SCR) catalyst, of V2O5−WO3/TiO2 type, has been studied through comparisons with results from a full-scale biomass combustion plant to that with laboratory
experiments. In the latter, the catalyst was exposed to KCl and K2SO4 by both wet impregnation with diluted salt solutions and deposition of generated submicrometer aerosol particles by means
of an electrostatic field. The reactivity of fresh and deactivated samples was examined in the SCR reaction. Chemical and
physical characterizations were focusing on internal structures and chemical composition. Deposition of submicrometer sized
particles on the monolithic SCR catalyst was shown to induce deactivation with characteristics resembling those obtained in
a commercial biomass combustion plant. 相似文献
4.
5.
Francesco Castellino Anker Degn Jensen Jan Erik Johnsson Rasmus Fehrmann 《Applied catalysis. B, Environmental》2009,86(3-4):206-215
A commercial V2O5–WO3–TiO2 corrugated-type SCR monolith has been exposed for 1000 h in a pilot-scale setup to a flue gas doped with KCl, Ca(OH)2, H3PO4 and H2SO4 by spraying a water solution of the components into the hot flue gas. The mixture composition has been adjusted in order to have P/K and P/Ca ratios equal to 2 and 0.8, respectively. At these conditions, it is suggested that all the K released during biomass combustion gets captured in P–K–Ca particles and the Cl is released in the gas phase as HCl, thus limiting deposition and corrosion problems at the superheater exchangers during biomass combustion. Aerosol measurements carried out by using a SMPS and a low pressure cascade impactor have shown two distinct particle populations with volume-based mean diameters equal to 12 and 300 nm, respectively. The small particles have been associated to polyphosphoric acids formed by condensation of H3PO4, whereas the larger particles are due to P–K–Ca salts formed during evaporation of the water solution. No Cl has been found in the collected particles. During the initial 240 h of exposure, the catalyst element lost about 20% of its original activity. The deactivation then proceeded at slower rates, and after 1000 h the relative activity loss had increased to 25%. Different samples of the spent catalyst have been characterized after 453 h and at the end of the experiment by bulk chemical analysis, Hg-porosimetry and SEM-EDX. NH3-chemisorption tests on the spent elements and activity tests on catalyst powders obtained by crushing the monolith have also been carried out. From the characterization, it was found that neither K nor Ca were able to penetrate the catalyst walls, but only accumulated on the outer surface. Poisoning by K has then been limited to the most outer catalyst surface and did not proceed at the fast rates known for KCl. This fact indicates that binding K in P–K–Ca compounds is an effective way to reduce the negative influence of alkali metals on the lifetime of the vanadia-based SCR catalysts. On the other hand, P-deposition was favoured by the formation of the polyphosphoric acids, and up to 1.8 wt% P was accumulated in the catalyst walls. Deactivation by polyphosphoric acids proceeded at about 0.2% day−1. About 6–7% of the initial activity was lost due to the accumulation of these species. However, the measured relative activity reached a steady-state level during the last 240 h of exposure indicating that the P-concentration in the bulk reached a steady-state level due to the simultaneous hydrolysis of the polyphosphoric acids. 相似文献
6.
Aditya Savara Mei-Jun Li Wolfgang M.H. Sachtler Eric Weitz 《Applied catalysis. B, Environmental》2008,81(3-4):251-257
Ammonium nitrate is thermally stable below 250 °C and could potentially deactivate low temperature NOx reduction catalysts by blocking active sites. It is shown that NO reduces neat NH4NO3 above its 170 °C melting point, while acidic solids catalyze this reaction even at temperatures below 100 °C. NO2, a product of the reduction, can dimerize and then dissociate in molten NH4NO3 to NO+ + NO3−, and may be stabilized within the melt as either an adduct or as HNO2 formed from the hydrolysis of NO+ or N2O4. The other product of reduction, NH4NO2, readily decomposes at ≤100 °C to N2 and H2O, the desired end products of DeNOx catalysis. A mechanism for the acid catalyzed reduction of NH4NO3 by NO is proposed, with HNO3 as an intermediate. These findings indicate that the use of acidic catalysts or promoters in DeNOx systems could help mitigate catalyst deactivation at low operating temperatures (<150 °C). 相似文献
7.
Yong Liu Ming Meng Xin-Gang Li Li-Hong Guo Yu-Qing Zha 《Chemical Engineering Research and Design》2008,86(8):932-940
The NOx storage and reduction (NSR) catalysts Pt/K/TiO2–ZrO2 were prepared by an impregnation method. The techniques of XRD, NH3-TPD, CO2-TPD, H2-TPR and in situDRIFTS were employed to investigate their NOx storage behavior and sulfur-resisting performance. It is revealed that the storage capacity and sulfur-resisting ability of these catalysts depend strongly on the calcination temperature of the support. The catalyst with theist support calcined at 500 °C, exhibits the largest specific surface area but the lowest storage capacity. With increasing calcination temperature, the NOx storage capacity of the catalyst improves greatly, but the sulfur-resisting ability of the catalyst decreases. In situ DRIFTS results show that free nitrate species and bulk sulfates are the main storage and sulfation species, respectively, for all the catalysts studied. The CO2-TPD results indicate that the decomposition performance of K2CO3 is largely determined by the surface property of the TiO2–ZrO2 support. The interaction between the surface hydroxyl of the support and K2CO3 promotes the decomposition of K2CO3 to form –OK groups bound to the support, leading to low NOx storage capacity but high sulfur-resisting ability, while the interaction between the highly dispersed K2CO3 species and Lewis acid sites gives rise to high NOx storage capacity but decreased sulfur-resisting ability. The optimal calcination temperature of TiO2–ZrO2 support is 650 °C. 相似文献
8.
Jiawei Wang Jing Liu Guiling Yang Xianfa Zhang Xuedong Yan Xiumei Pan Rongshun Wang 《Electrochimica acta》2009,54(26):6451-6454
Polyethylene glycol (PEG, mean molecular weight of 10,000) has been used to prepare a Li3V2(PO4)3/C cathode material by a simple solid-state reaction. The Raman spectra shows that the coating carbon has a good structure with a low ID/IG ratio. The images of SEM and TEM show that the carbon is dispersed between the Li3V2(PO4)3 particles, which improves the electrical contact between the corresponding particles. The electronic conductivity of Li3V2(PO4)3/C composite is 7.0 × 10−1 S/cm, increased by seven orders of magnitude compared with the pristine Li3V2(PO4)3 (2.3 × 10−8 S/cm). At a low discharge rate of 0.28C, the sample presents a high discharge capacity of 131.2 mAh/g, almost achieving the theoretical capacity (132 mAh/g) for the reversible cycling of two lithium. After 500 cycles, the discharge capacity is 123.9 mAh/g with only 5.6% fading of the initial specific capacity. The Li3V2(PO4)3/C material also exhibits an excellent rate capability with high discharge capacities of 115.2 mAh/g at 1C and 106.4 mAh/g at 5C. 相似文献
9.
Debao Li Cheng YangNing Zhao Huijie QiWenhuai Li Yuhan SunBing Zhong 《Fuel Processing Technology》2007
Ni modified K2CO3/MoS2 catalyst was prepared and the performance of higher alcohol synthesis catalyst was investigated under the conditions: T = 280–340 °C, H2/CO (molar radio) = 2.0, GHSV = 3000 h− 1, and P = 10.0 MPa. Compared with conventional K2CO3/MoS2 catalyst, Ni/K2CO3/MoS2 catalyst showed higher activity and higher selectivity to C2+OH. The optimum temperature range was 320–340 °C and the maximum space-time yield (STY) of alcohol 0.30 g/ml h was obtained at 320 °C. The selectivity to hydrocarbons over Ni/K2CO3/MoS2 was higher, however, it was close to that of K2CO3/MoS2 catalyst as the temperature increased. The results indicated that nickel was an efficient promoter to improve the activity and selectivity of K2CO3/MoS2 catalyst. 相似文献
10.
This work investigates the improvement of Ni/Al2O3 catalyst stability by ZrO2 addition for H2 gas production from CH4/CO2 reforming reactions. The initial effect of Ni addition was followed by the effect of increasing operating temperature to 500–700 °C as well as the effect of ZrO2 loading and the promoted catalyst preparation methods by using a feed gas mixture at a CH4:CO2 ratio of 1:1.25. The experimental results showed that a high reaction temperature of 700 °C was favored by an endothermic dry reforming reaction. In this reaction the deactivation of Ni/Al2O3 was mainly due to coke deposition. This deactivation was evidently inhibited by ZrO2, as it enhances dissociation of CO2 forming oxygen intermediates near the contact between ZrO2 and nickel where the deposited coke is gasified afterwards. The texture of the catalyst or BET surface area was affected by the catalyst preparation method. The change of the catalyst texture resulted from the formation of ZrO2–Al2O3 composite and the plugging of Al2O3 pore by ZrO2. The 15% Ni/10% ZrO2/Al2O3 co-impregnated catalyst showed a higher BET surface area and catalytic activity than the sequentially impregnated catalyst whereas coke inhibition capability of the promoted catalysts prepared by either method was comparable. Further study on long-term catalyst stability should be made. 相似文献
11.
Weijie Cai Fagen Wang A.C. Van Veen H. Provendier C. Mirodatos Wenjie Shen 《Catalysis Today》2008,138(3-4):152
Hydrogen production from ethanol by autothermal reforming over an Rh/CeO2 catalyst was investigated with a stoichiometric feed composition. Ethanol as well as the reaction intermediates like acetaldehyde and acetone was entirely converted to hydrogen and C1 products at 673 K, and methane steam reforming and reverse water gas shift were the major reactions above 823 K. The Rh/CeO2 catalyst exhibited stable activity and selectivity during 70 h on-stream operation at 823–923 K without obvious deactivation evidenced by the constant effluent gas composition. Structural analysis of the used catalyst revealed that CeO2 prevented effectively the highly dispersed Rh particles with sizes of 1–3 nm from sintering and thus maintained sufficient Rh–CeO2 interfacial areas, which facilitated coke gasification through the high oxygen storage-release capacity. 相似文献
12.
K. Rida A. Benabbas F. Bouremmad M.A. Pea A. Martínez-Arias 《Catalysis communications》2006,7(12):963-968
Catalytic CO oxidation and C3H6 combustion have been studied over La1−xSrxCrO3 (x = 0.0–0.3) oxides prepared by solid-state reaction and characterised by X-ray diffraction (XRD), nitrogen adsorption (BET analysis) and X-ray photoelectron spectroscopy (XPS). The expected orthorhombic perovskite structure of the chromite is observed for all levels of substitution. However, surface segregation of strontium along with a chromium oxidation process, leading to formation of Cr6+-containing phases, is produced upon increasing x and shown to be detrimental to the catalytic activity. Maximum activity is achieved for the catalyst with x = 0.1 in which mixed oxide formation upon substitution of lanthanum by strontium in the chromite becomes maximised. 相似文献
13.
The influence of CO2 on the deactivation of Co/γ-Al2O3 Fischer–Tropsch (FT) catalyst in CO hydrogenation has been investigated. The presence of CO2 in the feed stream reveals a negative effect on catalyst stability and in the formation of heavy hydrocarbons. The CO2 acts as a mild oxidizing agent on cobalt metal during Fischer–Tropsch synthesis. During FT synthesis on Co/γ-Al2O3 of 70 h, the CO conversion and C5+ selectivity in the presence of CO2 decreased more significantly than in the absence of CO2. CO2 is found to be responsible for the partial oxidation of surface cobalt metal at FT synthesis environment with the co-existence of generated water. 相似文献
14.
S. Mostafa Jason R. Croy H. Heinrich B. Roldan Cuenya 《Applied Catalysis A: General》2009,366(2):353-362
This article discusses the performance of ZrO2-supported size-selected Pt nanoparticles for the decomposition of methanol, ethanol, 2-propanol, and 2-butanol. The potential of each alcohol for the production of H2 and other relevant products in the presence of a catalyst is studied in a packed-bed mass flow reactor operating at atmospheric pressure. All the alcohols studied show some decomposition activity below 200 °C which increased with increasing temperature. In all cases, high selectivity towards H2 formation is observed. With the exception of methanol, all alcohol conversion reactions lead to catalyst deactivation at high temperatures (T > 250 °C for 2-propanol and 2-butanol, T > 325 °C for ethanol) due to carbon poisoning. However, long-term catalyst deactivation can be avoided by optimizing reaction conditions such as operating temperature. 相似文献
15.
Yingxin Liu Tiefeng Xing Zuojun Wei Xiaonian Li Wei Yan 《Catalysis communications》2009,10(15):2023-2026
Au/TiO2 catalysts with different gold loadings were prepared by deposition–precipitation method and used for the liquid phase hydrogenation of phthalic anhydride. All the studied Au/TiO2 catalysts exhibited excellent activity with high selectivity (>92%) to phthalide under mild reaction conditions (180 °C and 3.0 MPa H2). Specially, catalysts with 2–3 wt.% gold loading were highly active and selective for the formation of phthalide. When reused, the catalyst showed a certain deactivation, but still was highly selective to phthalide. The deactivation was attributed to the leaching of gold, collapse of the pore structure and accumulation of organic species on the surface. 相似文献
16.
Ultrafine Cu0.1Ce0.5Zr0.4O2−δ catalyst operated in a fluidized bed reactor was found to be very effective for complete oxidation of dilute benzene in air. The complete conversion of benzene could be achieved at reaction temperature as low as 220 °C. The mechanism of benzene oxidation over the Cu0.1Ce0.5Zr0.4O2−δ catalyst was investigated by conducting pulse reaction of pure benzene in the absence of O2 over the catalyst and the results indicated the involvement of lattice oxygen from the catalyst in benzene oxidation. 相似文献
17.
Shuang Chen Ming Ye Hao-Hong Chen Xin-Xin Yang Jing-Tai Zhao 《Journal of Inorganic and Organometallic Polymers and Materials》2009,19(2):139-142
Boron phosphate (BPO4) is a well known catalyst for a range of organic chemical reactions. In this paper, we report the preparations and characterizations
of nano-sized BPO4 and nano-BPO4-based core-shell spheres. The samples were synthesized hydrothermally using H3BO3, H3PO4 and short chain n-alkylamines (n = 3, 4) as starting materials. The resulting products were characterized by powder X-ray diffraction (XRD), Fourier transform
infrared spectroscopy (FT-IR), scan electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. A
possible mechanism for the formation of the materials is also discussed. 相似文献
18.
Bo-Hyuk Jang Tae-Hun Yeon Hyun-Sik Han Yong-Ki Park Jae-Eui Yie 《Catalysis Letters》2001,77(1-3):21-28
Barium-containing NO
x
storage catalyst showed serious deactivation under thermal exposure at high temperatures. To elucidate the thermal deterioration of the NO
x
storage catalyst, four types of model catalyst, Pt/Al2O3, Ba/Al2O3, Pt–Ba/Al2O3, and a physical mixture of Pt/Al2O3 + Ba/Al2O3 were prepared and their physicochemical properties such as BET, NO TPD, TGA/DSC, XRD, and XPS were evaluated while the thermal aging temperature was increased from 550 to 1050°C. The fresh Pt–Ba/Al2O3 showed a sorption capacity of 3.35 wt%/g-cat. but the aged one revealed a reduced capacity of 2.28 wt%/g-cat. corresponding to 68% of the fresh one. It was found that this reduced sorption capacity was directly related to the deterioration of the NO
x
storage catalyst by thermal aging. The Ba on Ba/Al2O3 and Pt–Ba/Al2O3 catalysts began to interact with alumina to form Ba–Al solid alloy above 600°C and then transformed into stable BaAl2O4 having a spinel structure. However, no phase transition was observed in the Pt/Al2O3 catalyst having no barium component, even after aging at 1050°C. 相似文献
19.
Chih-Hung Chu Chih-Peng Lin Shaw-Bing Wen Yun-Hwei Shen 《Ceramics International》2009,35(8):3455-3461
Aluminum nitride (AlN) ceramics, prepared with Y2O3 and CaO sintering additives, have been densified in an Al2O3 crucible at temperatures of up to 1650 °C and 1700 °C using a conventional MoSi2 heating element furnace. The results of this study show that relative densities in excess of 99% of theoretical and a relatively high-thermal conductivity of 147 W m−1 K−1 have been achieved for feedstock materials prepared with combined addition of 1 wt.% Y2O3 and 1 wt.% CaO. All of the phases in sintered samples have been shown to be crystalline AlN and minor amount of secondary phases, were detected such as enriched Y- and Ca-aluminates by the XRD patterns, back-scattered imagery and microprobe analysis. The advantage of using the particular experimental system and sintering condition is considered to be amenable to lower production cost and enhance the feasibility of mass production. Critical temperature for AlN densification to obtain the highest density is about 1650 °C. 相似文献
20.
Ensheng Zhan Yong Li Junlong Liu Xiumin Huang Wenjie Shen 《Catalysis communications》2009,10(15):2051-2055
Mesoporous TiO2 was prepared by simply controlling the hydrolysis of Ti(OBu)4 with the help of acetic acid. The mesoporous TiO2 had a well-crystallized anatase phase and a high surface area of 290 m2 g−1 with a pore size of about 4 nm. The anatase phase and the mesoporous structure were maintained in the VOx/TiO2 catalyst with a monolayer dispersion of V2O5, however, the surface area decreased to 126 m2 g−1. The catalyst was highly active and selective for methanol oxidation, giving about 55% conversion of methanol and 85% selectivity to dimethoxymethane at 423 K. 相似文献