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1.
TiO 2-SiO 2 with various compositions prepared by the coprecipitation method and vanadia loaded on TiO 2-SiO 2 were investigated with respect to their physico-chemical characteristics and catalytic behavior in SCR of NO by NH 3 and in the undesired oxidation of SO 2 to SO 3, using BET, XRD, XPS, NH 3-TPD, acidity measurement by the titration method and activity test. TiO 2-SiO 2, compared with pure TiO 2, exhibits a remarkably stronger acidity, a higher BET surface area, a lower crystallinity of anatase titania and results in allowing a good thermal stability and a higher vanadia dispersion on the support up to high loadings of 15 wt% V 2O 5. The SCR activity and N 2 selectivity are found to be more excellent over vanadia loaded on TiO 2-SiO 2 with 10–20 mol% of SiO 2 than over that on pure TiO 2, and this is considered to be associated with highly dispersed vanadia on the supports and large amounts of NH 3 adsorbed on the catalysts. With increasing SiO 2 content, the remarkable activity decrease in the oxidation of SO 2 to SO 3, favorable for industrial SCR catalysts, was also observed, strongly depending on the existence of vanadium species of the oxidation state close to V 4+ on TiO 2-SiO 2, while V 5+ exists on TiO 2, according to XPS. It is concluded that vanadia loaded on Ti-rich TiO 2-SiO 2 with low SiO 2 content is suitable as SCR catalysts for sulfur-containing exhaust gases due to showing not only the excellent de-NO x activity but also the low SO 2 oxidation performance. 相似文献
2.
Operating the SCR DeNO x reactor at temperatures below 200 °C results in a considerable saving in operating costs. Plant experience shows that on the catalysts in these second generation DeNO x plants, even for flue gases with SO 2 concentration below 10 mg/m 3, over 1–2 years operating time sizeable quantities of ammonium sulfates accumulate. Ammonium sulfates deposited on V 2O 5–WO 3/TiO 2 catalysts react with NO x to nitrogen and sulfuric acid. Second-order rate constants of this reaction for temperatures of 170 °C have been derived. It could be shown that the sulfuric acid formed on the catalyst is displaced by water vapour and desorbs resulting in gas phase concentrations of up to 6.5 mg acid/m 3 flue gas. Plant equipment downstream of the ammonium sulfate containing low temperature DeNO x catalysts has to be protected against the corrosive action of the sulfuric acid in the flue gases leaving the DeNO x reactor. 相似文献
3.
The effect of tungsten and barium on the thermal stability of V 2O 5/TiO 2 catalyst for NO reduction by NH 3 was examined over a fixed bed flow reactor system. The activity of V 2O 5/sulfated TiO 2 catalyst gradually decreased with respect to the thermal aging time at 600 °C. The addition of tungsten to the catalyst surface significantly enhanced the thermal stability of V 2O 5 catalyst supported on sulfated TiO 2. On the basis of Raman and XRD measurements, the tungsten on the catalyst surface was identified as suppressing the progressive transformation of monomeric vanadyl species into crystalline V 2O 5 and of anatase into rutile phase of TiO 2. However, the NO removal activity of V 2O 5/sulfated TiO 2 catalyst including barium markedly decreased after a short aging time, 6 h at 600 °C. This may be due to the transformation of vanadium species to inactive V–O–Ba compound by the interaction with BaO which was formed by the decomposition of BaSO 4 on the catalyst surface at high reaction temperature of 600 °C. The addition of SO 2 to the feed gas stream could partly restore the NO removal activity of thermally aged V 2O 5/sulfated TiO 2 catalyst containing barium. 相似文献
4.
利用溶胶-凝胶技术原位合成一系列不同V 2O 5担载量的V 2O 5/TiO 2催化剂,通过BET、XRD、NH 3-TPD及紫外-可见光等手段对催化剂进行表征。结果表明:制备的催化剂均具有介孔结构,V 2O 5在TiO 2表面高度分散,且存在3种典型的酸性位。通过选择性催化还原反应对V 2O 5/TiO 2催化剂进行活性评价,结果显示随着V 2O 5含量的增加,NO转化率大于75%的温度窗口向低温方向偏移,含10% (质量分数)V 2O 5的催化剂的NO转化率为80%的温度窗口最宽为200~450℃,240℃时20 h连续实验表现出稳定的抗硫抗水性能。结合紫外-可见光谱分析,揭示了钒掺杂所形成的单聚和低聚钒酸盐为催化剂的活性组分。 相似文献
5.
The characteristics of sulfated V 2O 5/TiO 2 honeycomb catalyst from metatitanic acid (MTA) were studied in the practical conditions of pilot plant using high dust flue gas from coal fired utility boiler. The effects of reaction temperature, NH 3/NO mole ratio, space velocity and operation time on the reduction of nitric oxide (NO) were mainly investigated for engineering application. The catalyst showed high NO reduction of about 90% at a space velocity of 4000 h −1, NH 3/NO mole ratio of 1.0 and reaction temperature of 300–400 °C. The efficiency of this catalyst remained constant during the present experiment of 2400 h and the erosion by fly ash was lower than that of the commercial catalysts. These results clearly demonstrate the high potential for this catalyst to be applied commercially for the control of NO x emissions from coal fired utility boiler. 相似文献
6.
采用V_2O_5/WO_3-TiO_2作为脱硝催化剂,考察活性组分V_2O_5和助剂WO_3负载量对催化剂脱硝活性和抗硫抗水性能的影响。结果表明,3%V_2O_5/x WO_3-TiO_2催化剂(x=3%、4%、5%、6%、7%、8%、9%、10%)上NOx转化率随着WO_3负载量增加而升高,催化剂反应温度窗口不断拓宽。单独通水蒸汽及同时通SO2和水蒸汽对催化剂的毒害作用均较强,表明H2O和NH3的竞争吸附是催化剂抗硫抗水性能较差的重要原因。SO_2与H_2O和NH_3反应生成亚硫酸铵盐和硫酸铵盐,导致催化剂孔隙堵塞,催化活性降低。 相似文献
7.
Two series of catalysts, V 2O 5/TiO 2 and modified V 2O 5/TiO 2, were prepared with a conventional impregnation method. They were tested in the selective oxidation of toluene to benzoic acid under microwave irradiation. The reaction conditions were optimized over V 2O 5/TiO 2. It was found that in the microwave catalytic process the optimum reactor bed temperature of the titled reaction decreases to 500 K (600 K in the conventional process). The modification of V 2O 5/TiO 2 with MoO 3, WO 3, Nb 2O 5 or Ta 2O 5, which has no negative influence on the reaction in the conventional catalytic process, can greatly promote the catalytic activities in the microwave process, leading to a high yield of benzoic acid (41%). The effects of microwave electromagnetic field on the catalysts are discussed. 相似文献
8.
Catalytic performance of Sn/Al 2O 3 catalysts prepared by impregnation (IM) and sol–gel (SG) method for selective catalytic reduction of NO x by propene under lean burn condition were investigated. The physical properties of catalyst were characterized by BET, XRD, XPS and TPD. The results showed that NO 2 had higher reactivity than NO to nitrogen, the maximum NO conversion was 82% on the 5% Sn/Al 2O 3 (SG) catalyst, and the maximum NO 2 conversion reached nearly 100% around 425 °C. Such a temperature of maximum NO conversion was in accordance with those of NO x desorption accompanied with O 2 around 450 °C. The activity of NO reduction was enhanced remarkably by the presence of H 2O and SO 2 at low temperature, and the temperature window was also broadened in the presence of H 2O and SO 2, however the NO x desorption and NO conversion decreased sharply on the 300 ppm SO 2 treated catalyst, the catalytic activity was inhibited by the presence of SO 2 due to formation of sulfate species (SO 42−) on the catalysts. The presence of oxygen played an essential role in NO reduction, and the activity of the 5% Sn/Al 2O 3 (SG) was not decreased in the presence of large oxygen. 相似文献
9.
Combined effect of H 2O and SO 2 on V 2O 5/AC the activity of catalyst for selective catalytic reduction (SCR) of NO with NH 3 at lower temperatures was studied. In the absence of SO 2, H 2O inhibits the catalytic activity, which may be attributed to competitive adsorption of H 2O and reactants (NO and/or NH 3). Although SO 2 promotes the SCR activity of the V 2O 5/AC catalyst in the absence of H 2O, it speeds the deactivation of the catalyst in the presence of H 2O. The dual effect of SO 2 is attributed to the SO 42− formed on the catalyst surface, which stays as ammonium-sulfate salts on the catalyst surface. In the absence of H 2O, a small amount of ammonium-sulfate salts deposits on the surface of the catalyst, which promote the SCR activity; in the presence of H 2O, however, the deposition rate of ammonium-sulfate salts is much greater, which results in blocking of the catalyst pores and deactivates the catalyst. Decreasing V 2O 5 loading decreases the deactivation rate of the catalyst. The catalyst can be used stably at a space velocity of 9000 h −1 and temperature of 250 °C. 相似文献
10.
In situ Raman spectroscopy was used for studying the ternary 2% CrO 3–6% V 2O 5/TiO 2 catalyst, for which a synergistic effect between vanadia and chromia leads to enhanced catalytic performance for the selective catalytic reduction (SCR) of NO with NH 3. The structural properties of this catalyst were studied under NH 3/NO/O 2/N 2/SO 2/H 2O atmospheres at temperatures up to 400 °C and major structural interactions between the surface chromia and vanadia species are observed. The effects of oxygen, ammonia, water vapor and sulfur dioxide presence on the in situ Raman spectra are presented and discussed. 相似文献
11.
A novel TiO 2/Al 2O 3/cordierite honeycomb-supported V 2O 5–MoO 3–WO 3 monolithic catalyst was studied for the selective reduction of NO with NH 3. The effects of reaction temperature, space velocity, NH 3/NO ratio and oxygen content on SCR activity were evaluated. Two other V 2O 5–MoO 3–WO 3 monolithic catalysts supported on Al 2O 3/cordierite honeycomb or TiO 2/cordierite honeycomb support, two types of pellet catalysts supported on TiO 2/Al 2O 3 or Al 2O 3, as well as three types of pellet catalysts V 2O 5–MoO 3–WO 3–Al 2O 3 and V 2O 5–MoO 3–WO 3–TiO 2 were tested for comparison. The experiment results show that this catalyst has a higher catalytic activity for SCR with comparison to others. The results of characterization show, the preparation method of this catalyst can give rise to a higher BET surface area and pore volume, which is strongly related with the highly active performance of this catalyst. At the same time, the function of the combined carrier of TiO 2/Al 2O 3 cannot be excluded. 相似文献
12.
A series of B-doped V 2O 5/TiO 2 catalysts has been prepared the by sol-gel and impregnation methods to investigate the influence of B-doping on the selective catalytic reduction (SCR) of NO x with NH 3. X-ray diffraction, Brunauer-Emmett-Teller specific surface area, scanning electron microscope, X-ray photoelectron spectroscopy, temperature-programmed reduction of H 2 and temperature-programmed desorption of NH 3 technology were used to study the effect of the B-doping on the structure and NH 3-SCR activity of V 2O 5/TiO 2 catalysts. The experimental results demonstrated that the introduction of B not only improved the low-temperature SCR activity of the catalysts, but also broadened the activity temperature window. The best SCR activity in the entire test temperature range is obtained for VTiB 2.0 with 2.0% doping amount of B and the NO x conversion rate is up to 94.3% at 210 ℃. The crystal phase, specific surface area, valence state reducibility and surface acidity of the active components for the as-prepared catalysts are significantly affected by the B-doping, resulting in an improved NH 3-SCR performance. These results suggest that the V 2O 5/TiO 2 catalysts with an appropriate B content afford good candidates for SCR in the low temperature window. 相似文献
13.
The physico-chemical characteristics and the reactivity of sub-monolayer V 2O 5-WO 3/TiO 2 deNO x catalysts is investigated in this work by EPR, FT-IR and reactivity tests under transient conditions. EPR indicates that tetravalent vanadium ions both in magnetically isolated form and in clustered, magnetically interacting form are present over the TiO 2 surface. The presence of tungsten oxide stabilizes the surface V IV and modifies the redox properties of V 2O 5/TiO 2 samples. Ammonia adsorbs on the catalysts surface in the form of molecularly coordinated species and of ammonium ions. Upon heating, activation of ammonia via an amide species is apparent. V 2O 5-WO 3/TiO 2 catalysts exhibits higher activity than the binary V 2O 5/TiO 2 and WO 3/TiO 2 reference sample. This is related to both higher redox properties and higher surface acidity of the ternary catalysts. Results suggest that the catalyst redox properties control the reactivity of the samples at low temperatures whereas the surface acidity plays an important role in the adsorption and activation of ammonia at high temperatures. 相似文献
14.
A novel activated carbon-supported vanadium oxide catalyst was studied for SCR of NO with NH 3 at low temperatures (100 – 250°C). The effects of reaction temperature, preparation conditions and SO 2 on SCR activity were evaluated. The results show that this catalyst has a high catalytic activity for NO–NH 3–O 2 reaction at low temperatures. Preoxidation of the calcined catalyst helps improve catalytic activity. V 2O 5 loading, other than calcination temperature, gives a significant influence on the activity. SO 2 in the flue gas does not de-activate the catalyst but improves it. A stability test of more than 260 h shows that the catalyst is highly active and stable in the presence of SO 2. 相似文献
15.
The industrial SO 2 oxidation catalyst VK69 deactivates at around 440°C in a 10% SO 2, 11% O 2, 79% N 2 gas mixture. In situ EPR measurements show that the deactivation is caused by the precipitation of V(IV) compounds. DeNO x catalysts based on V 2O 5/TiO 2, the TiO 2 support, analytical grade anatase and transition metal-exchanged Al-PILCs (pillared clay) have been characterized by EPR spectroscopy and the catalytic activity of the catalysts monitored up to 500°C. Depending on the exchanged metal ion, a relatively large temperature range for the catalytic activity towards the SCR reaction was observed. 相似文献
16.
We investigated the suppression of SO 2 oxidation activity by vanadium oxide in Pt-based diesel oxidation catalyst using reaction experiments, temperature programmed desorption (TPD), infrared (IR) and X-ray photoelectron spectroscopy (XPS). There was no interaction between Pt and S indicated by the XPS results. SO 2 was not adsorbed on Pt at room temperature indicated by the absence of peak arising from SO 2 in SO 2 TPD spectra. SO 2 molecules were adsorbed on the hydroxyl groups of TiO 2 and migrated to Pt particles to react with oxygen adsorbed on it. V 2O 5 decreased the adsorption of SO 2 on TiO 2 by the blockage of V 2O 5 on TiO 2. 相似文献
17.
A multi-component NO x-trap catalyst consisting of Pt and K supported on γ-Al 2O 3 was studied at 250 °C to determine the roles of the individual catalyst components, to identify the adsorbing species during the lean capture cycle, and to assess the effects of H 2O and CO 2 on NO x storage. The Al 2O 3 support was shown to have NO x trapping capability with and without Pt present (at 250 °C Pt/Al 2O 3 adsorbs 2.3 μmols NO x/m 2). NO x is primarily trapped on Al 2O 3 in the form of nitrates with monodentate, chelating and bridged forms apparent in Diffuse Reflectance mid-Infrared Fourier Transform Spectroscopy (DRIFTS) analysis. The addition of K to the catalyst increases the adsorption capacity to 6.2 μmols NO x/m 2, and the primary storage form on K is a free nitrate ion. Quantitative DRIFTS analysis shows that 12% of the nitrates on a Pt/K/Al 2O 3 catalyst are coordinated on the Al 2O 3 support at saturation. When 5% CO2 was included in a feed stream with 300 ppm NO and 12% O2, the amount of K-based nitrate storage decreased by 45% after 1 h on stream due to the competition of adsorbed free nitrates with carboxylates for adsorption sites. When 5% H2O was included in a feed stream with 300 ppm NO and 12% O2, the amount of K-based nitrate storage decreased by only 16% after 1 h, but the Al2O3-based nitrates decreased by 92%. Interestingly, with both 5% CO2 and 5% H2O in the feed, the total storage only decreased by 11%, as the hydroxyl groups generated on Al2O3 destabilized the K–CO2 bond; specifically, H2O mitigates the NOx storage capacity losses associated with carboxylate competition. 相似文献
18.
This work investigates performances of supported transition-metal oxide catalysts for the catalytic reduction of SO 2 with C 2H 4 as a reducing agent. Experimental results indicate that the active species, the support, the feed ratio of C 2H 4/SO 2, and pretreatment are all important factors affecting catalyst activity. Fe 2O 3/γ-Al 2O 3 was found to be the most active catalyst among six γ-Al 2O 3-supported metal oxide catalysts tested. With Fe 2O 3 as the active species, of the supports tested, CeO 2 is the most suitable one. Using this Fe 2O 3/CeO 2 catalyst, we found that the optimal Fe content is 10 wt.%, the optimal feed ratio of C 2H 4/SO 2 is 1:1, and the catalyst presulfidized by H 2+H 2S exhibits a higher performance than those pretreated with H 2 or He. Although the feed concentrations of C 2H 4:SO 2 being 3000:3000 ppm provide a higher conversion of SO 2, the sulfur yield decreases drastically at temperatures above 300 °C. With higher feed concentrations, maximum yield appears at higher temperatures. The C 2H 4 temperature-programmed desorption (C 2H 4-TPD) and SO 2-TPD desorption patterns illustrate that Fe 2O 3/CeO 2 can adsorb and desorb C 2H 4 and SO 2 more easily than can Fe 2O 3/γ-Al 2O 3. Moreover, the SO 2-TPD patterns further show that Fe 2O 3/γ-Al 2O 3 is more seriously inhibited by SO 2. These findings may properly explain why Fe 2O 3/CeO 2 has a higher activity for the reduction of SO 2. 相似文献
19.
Vanadium oxide spread highly on TiO 2 (anatase, A) and SnO 2, and rather densely on TiO 2 (rutile, R) and ZrO 2 to make the monolayer in less than 4–5 V nm −2. Profile of acid site of the monolayer was measured by temperature programmed desorption of ammonia, and its relation with the surface oxidation state was studied. The acid site density was high on the V 2O 5/TiO 2 (A) independent of the degree of oxidation. On the other hand, that of V 2O 5/TiO 2 (R) and V 2O 5/ZrO 2 depended on the oxidation state, and the high value of the concentration was observed on the oxidized one. The strength of acid site generated on the V 2O 5 monolayer on TiO 2 was as high as on the HZSM-5 zeolite. Turnover frequency (TOF) of propane conversion, and product selectivity were measured in propane oxidation. Among tested oxides, the V 2O 5/TiO 2 (A) showed the high TOF and selectivity to form propylene, while those loaded on TiO 2 (R) and ZrO 2 the small TOF and poor selectivity. Therefore, the reaction profile of activity and selectivity could be related with the extent of spreading and solid acidity. An idea of limit of the acid site density ca. 1.5 nm −2 on the monolayer was elucidated. 相似文献
20.
Reaction activities of several developed catalysts for NO oxidation and NO x (NO + NO 2) reduction have been determined in a fixed bed differential reactor. Among all the catalysts tested, Co 3O 4 based catalysts are the most active ones for both NO oxidation and NO x reduction reactions even at high space velocity (SV) and low temperature in the fast selective catalytic reduction (SCR) process. Over Co 3O 4 catalyst, the effects of calcination temperatures, SO 2 concentration, optimum SV for 50% conversion of NO to NO 2 were determined. Also, Co 3O 4 based catalysts (Co 3O 4-WO 3) exhibit significantly higher conversion than all the developed DeNO x catalysts (supported/unsupported) having maximum conversion of NO x even at lower temperature and higher SV since the mixed oxide Co-W nanocomposite is formed. In case of the fast SCR, N 2O formation over Co 3O 4-WO 3 catalyst is far less than that over the other catalysts but the standard SCR produces high concentration of N 2O over all the catalysts. The effect of SO 2 concentration on NO x reduction is found to be almost negligible may be due to the presence of WO 3 that resists SO 2 oxidation. 相似文献
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