V_2O_5-WO_3/TiO_2脱硝催化剂的制备及抗硫性能

以锐钛矿TiO_2和TiO_2(P25)为载体,采用浸渍法制备V_2O_5-WO_3/TiO_2和V_2O_5-WO_3/TiO_2(P25)催化剂。利用FESEM、EDS、XRD、TGA和激光拉曼对催化剂进行表征。以NH_3为还原剂,考察载体晶型、钒质量分数、SO_2和活性测试时间对SCR催化还原NO的性能影响。结果表明,锐钛矿TiO_2载体制备的催化剂更利于选择性催化还原反应的发生,并且钒质量分数为3%时,锐钛矿TiO_2载体制备的催化剂脱硝性能较好且抗硫性能表现良好。在空速为10 000 h~(-1),反应温度为300℃,存在0.08%SO_2的条件下,催化剂在48 h内也能保持94%的脱硝率。     

低温高活性NO氧化催化剂Mn-V-Ce/TiO2的制备与性能

采用浸渍法制备了新型NO氧化催化剂Mn-V-Ce/TiO2,考察了组分配比、载体种类、焙烧温度等制备条件和反应温度、NO进口体积分数、O2含量、空速等操作条件对其催化活性的影响,对载体和催化剂分别进行了BET和XRD分析. 结果表明,10%Mn-3%V2O5-20%CeO2/TiO2在300℃焙烧6 h得到的Mn-V-Ce/TiO2具有最佳催化氧化活性,NO体积分数500′10-6,O2体积分数10%;空速8000 h-1、温度200℃或空速5000 h-1、温度175℃条件下,出口NOx的氧化度(NO2/NOx)均达到50%~60%,NOx能取得最大的吸收效率;250℃、8000 h-1时,氧化度可达74%;250℃、5000 h-1时,氧化度可达86.6%.     

活性炭负载磷钨酸用于烟气脱硝抗水性能实验研究

通过硝酸活化和高温水热活化方法对活性炭进行表面改性,之后在改性活性炭上负载不同含量的磷钨酸考察催化剂在有水蒸汽条件下的催化氧化脱硝催化活性,初始反应条件为：温度80 ℃,空速800 h^-1,O₂体积分数为5%、H₂O体积分数为4.2%、NO含量为443 mg·m^-3。通过FT-IR表征制备的催化剂评价前后表面有机活性基团的变化,将不同磷钨酸负载量下活性炭催化剂的脱硝活性评价结果和红外光谱结合,结果表明,湿气条件下,磷钨酸负载质量分数为10%时制备的催化剂能够较好地保持催化氧化脱硝稳定性,NO脱除效率约40%。考察不同操作参数,如温度、水蒸汽含量、O₂含量和空速对负载质量分数10%磷钨酸的活性炭催化剂催化氧化脱硝抗水性能的影响,最优操作条件：温度120 ℃,O₂体积分数8%,水蒸汽体积分数6%,空速1 000 h^-1,催化氧化反应的NO转化率达62%。     

新型脱硝催化剂的研制

采用等体积浸渍法制备以Cu和特种助剂为活性组分负载在特制 Ti-Al-O复合载体上的NH3选择性催化还原的新型脱硝催化剂,考察了在模拟硝酸尾气环境下该催化剂操作条件对其NH3-SCR活性的影响;探讨了H2 O对其活性的影响。结果表明,该催化剂具有很好的中温SCR活性,在空速10000 h-1、180～220℃、氨氮比0.8、O2体积分数5.5％、NO体积分数200×10-6条件下, NO转化率达99.5％。200℃下通水后,通水量为12.3％时,脱硝率降至14％;停止通水4 h后, N O转化率恢复至99.5％。     

活性焦低温催化氧化脱硝影响因素及机理

为了研究活性焦低温催化氧化NO特性,采用长周期试验,搭建固定床反应器试验台架,按照煤粉工业锅炉实际烟气组分模拟配制试验烟气。重点分析反应温度、O_2体积分数、空速及SO_2体积分数对脱硝效率影响,同时对反应前后的活性焦进行红外及热重分析。结果表明:当温度由50℃升到90℃时,活性焦脱硝效率显著下降,有效脱硝时间由81 h降到2.3 h;当O_2体积分数由0提高到10%时,有效脱硝时间由0.6 h提高到35 h;空速由500 h~(-1)升高到2 500 h~(-1)时,有效脱硝时间由15 h降到0.26 h;SO_2体积分数由0提高到200×10~(-6)时,有效脱硝时间由15 h降到1.6 h。红外及热重分析结果表明,低温时NO被催化氧化为NO_2,且大部分NO_2被活性焦吸附。     

CeO2/ACFN低温选择性催化还原烟气中的NO

制备了CeO2/ACFN(硝酸氧化处理的改性活性碳纤维)催化剂,对低温选择性催化还原(SCR)NO性能进行了考察.用SEM、BET和XRD进行催化剂结构特性表征,结果显示CeO2微粒高度分散在ACF的表面.实验表明,ACF先经过硝酸预氧化,然后再负载CeO2,能明显提高对NO的转化效率,CeO2负载量为9%(质量分数),180 ℃、空速为11000h-1时,CeO2/ACFN的NO脱除率为93.96%.     

载体对V_2O_5-MoO_3/TiO_2催化剂表面性质及其选择性催化还原脱硝性能的影响

采用比表面积分别为101.86 m2·g-1(A)、86.37 m2·g-1(B)和7.78(C)m2·g-1(C)的TiO_2载体,通过分步浸渍法制备V2O5-Mo O3/TiO_2(A,B,C)选择性催化还原脱硝催化剂。在空速为10 000 h-1和氨氮体积比1.0条件下,以TiO_2(A)与TiO_2(B)为载体制备的催化剂脱硝活性在反应温度窗口(350~450)℃超过90%,且具有良好的高温抗硫中毒性能和相对较小的氨气氧化率。而以TiO_2(C)为载体制备的脱硝催化剂活性温度窗口窄,在350℃时获得的最高脱硝活性仅为73%,且对NH3的氧化作用较强。利用X射线衍射、低温N2吸附-脱附、紫外-可见漫反射光谱、H2程序升温还原和NH3程序升温脱附等对载体和催化剂进行表征。结果表明,活性组分V2O5在载体TiO_2(A)上分散性良好,主要以孤立态钒氧物种形式存在,因此,以TiO_2(A)为载体制备的催化剂比表面积、氧化还原性和表面酸性等性能更优。     

商用选择性催化还原催化剂SO_2氧化率控制研究进展

选择性催化还原(SCR)法作为目前最成熟的氮氧化物(NO_x)控制技术被广泛地应用于燃煤电站等行业的NO_x排放控制过程,其核心是催化剂。商用SCR催化剂一般是以V_2O_5为活性组分、WO_3(或MoO_3)为催化助剂、TiO_2为载体的V_2O_5-WO_3(MoO_3)/TiO_2催化剂。该催化剂在催化NO_x还原的同时也会催化SO_2的氧化,生成的SO_3会给脱硝工程带来一系列的不利影响。基于此,本文首先介绍了钒钛催化剂催化氧化SO_2的反应机理及其研究进展,随后综述了影响SO_2氧化率的主要因素,主要包括催化剂中V_2O_5含量、催化助剂、飞灰、壁厚及烟气成分、反应温度等,并详细地分析了各因素对SO_2氧化率的影响特性。在此基础上,综述了控制SCR催化剂SO_2氧化率的方法。最后指出SO_2氧化率控制技术的发展对低SO_2氧化率脱硝催化剂的开发、失活催化剂的再生以及废弃催化剂的回用等均有着重要意义,是未来研究和开发的重点方向。     

Mn-Fe-Ce/Al_2O_3/堇青石催化剂低温NH_3-SCR脱硝性能研究

先采用溶胶凝胶法在堇青石蜂窝陶瓷载体上涂覆铝溶胶浆液,再通过浸渍法负载活性组分Mn和助剂,制备了NH3选择性催化还原NOx低温脱硝催化剂Mn-Fe-Ce/Al2O3/堇青石,实验结果显示:Ce和Fe的添加可以明显提高催化剂的低温脱硝活性,在体积空速4 000 h-1时和120℃条件下,NO转化率由86.3%提高到93.5%,并且在120~300℃范围内,NO的转化率均保持在93%以上。XRD、BET、NH3-TPD和H2-TPR结果表明:Fe和Ce改性后增加了催化剂的比表面积和孔体积、酸性位点、NH3的吸附能力和氧化能力,提高了催化剂的SCR活性。     

Mn-Fe-Ce/TiO2低温NH3选择性催化还原NO

采用浸渍法制备了MnO2-Fe2O3-CeO2/TiO2催化剂用于低温NH3选择性催化还原烟气中NO,考察了Mn, Fe, Ce含量及焙烧温度对NH3选择性催化还原NO的活性和抗水性能的影响. 在气体体积空速(GHSV)=24000 h-1, NH3/NO=0.8(j), 350℃煅烧和烟气含3%(j) O2的条件下,该系列催化剂的脱硝活性为MnO2-Fe2O3-CeO2/TiO2>MnO2- Fe2O3/TiO2>MnO2/TiO2,且在200℃时MnO2(10)-Fe2O3(5)-CeO2(5)/TiO2的脱硝率为95%. 对含10%(j)水蒸汽的烟气,MnO2(10)-Fe2O3(5)-CeO2(5)/TiO2的脱硝活性维持在87%;在10%(j)水蒸汽和100′10-6 SO2共存条件下,短时间内脱硝活性维持在55%.     

V2O5/（TiO2-SiO2）脱硝催化剂新型制备工艺及性能研究

将偏钒酸铵和羟丙基甲基纤维素搅拌混溶制备滴胶液,以自制的7孔圆柱蜂窝钛硅复合氧化物为载体,采用滴胶涂覆法制备了V₂O₅/（TiO₂-SiO₂）脱硝催化剂。通过X射线衍射（XRD）、程序升温还原（H₂-TPR）、比表面积分析（BET）和催化剂评价等方法对制备的脱硝催化剂进行分析表征。考察了五氧化二钒在钛硅复合氧化物载体上的分布、五氧化二钒涂覆量等对催化剂性能的影响,并就反应温度、反应空速、氨与一氧化氮物质的量比等条件对脱硝催化剂活性的影响进行了研究。实验结果表明,使用五氧化二钒涂覆量为1.2%（质量分数）的V₂O₅/（TiO₂-SiO₂）脱硝催化剂,在反应温度为320 ℃、空速为10 000 h^-1、氨与一氧化氮物质的量比为1.2条件下进行脱硝活性实验,一氧化氮转化率达到93.0%。经与工业脱硝催化剂对比实验表明,制备的V₂O₅/（TiO₂-SiO₂）脱硝催化剂性能优良,并且降低了钒的使用量,节约了生产成本,减少了环境污染。     

载体结构对锡铁负载型催化剂脱硝性能的影响

利用凹凸棒土（ATP）、活性炭（AC）、介孔硅（MCM-41）、二氧化钛（TiO₂）这4种孔结构不同的载体,通过水热法制备了以Fe₂O₃为催化剂主活性组分、SnO₂为辅活性组分的锡铁负载型催化剂。催化剂的微观结构通过BET和SEM测试,并在催化剂评价装置中模拟烟气组成,考察锡铁负载型催化剂在反应温度为80～280℃、脱硝空速为32000～48000h^-1范围内的选择性催化还原（SCR）性能。同时考察了SO₂与H₂O对1/2SnFe/ATP催化剂的影响。实验表明,载体可能为催化剂提供大量Brønsted酸性位点,有利于反应气体吸附。1/2SnFe/ATP催化剂表现出最佳的SCR脱硝性能,在200℃时实现最高96.4%的NO转化率,而且由其抗硫性及其抗水性实验表明：SO₂单独作用于催化剂时,脱硝效率降低迟缓,切断二氧化硫后仍能恢复到85%以上。同时加入水和二氧化硫后,将会导致脱硝效率急剧下降。停止加入后,催化剂效率又开始慢慢恢复,效率可以恢复达到70%以上。     

Catalytic oxidation of NO over Ce-doped Mn/TiO2

Mn-Ce/TiO₂ catalyst was prepared by impregnating Mn-Ce on TiO₂ and was characterized by XRD,BET and PL. The influences of Ce-doping concentration,loading,calcinations temperature,space velocity,inlet concentration of NO and volume fraction of oxygen on the performance of catalytic oxidation were examined. The results showed that the effect of doping Ce not only increased the surface area of MnO_x/TiO₂ but also enhanced the dispersion of active phase over TiO₂. At Ce-doping concentration of [Ce]/[Mn]=1/3,10% loading Mn-Ce/TiO₂ catalyst calcined at 300 ℃ for 3 h had high catalytic oxidation activity. When inlet concentration of NO was 300 μL/L,O₂ 10%,space velocity was 41000 h^－1,oxidation rate of NO over Mn-Ce/TiO₂ reached 58% at 200 ℃.     

TiO2-SiO2 and V2O5/TiO2-SiO2 catalyst: Physico-chemical characteristics and catalytic behavior in selective catalytic reduction of NO by NH3

TiO₂-SiO₂ with various compositions prepared by the coprecipitation method and vanadia loaded on TiO₂-SiO₂ were investigated with respect to their physico-chemical characteristics and catalytic behavior in SCR of NO by NH₃ and in the undesired oxidation of SO₂ to SO₃, using BET, XRD, XPS, NH₃-TPD, acidity measurement by the titration method and activity test. TiO₂-SiO₂, compared with pure TiO₂, 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% V₂O₅. The SCR activity and N₂ selectivity are found to be more excellent over vanadia loaded on TiO₂-SiO₂ with 10–20 mol% of SiO₂ than over that on pure TiO₂, and this is considered to be associated with highly dispersed vanadia on the supports and large amounts of NH₃ adsorbed on the catalysts. With increasing SiO₂ content, the remarkable activity decrease in the oxidation of SO₂ to SO₃, favorable for industrial SCR catalysts, was also observed, strongly depending on the existence of vanadium species of the oxidation state close to V⁴⁺ on TiO₂-SiO₂, while V⁵⁺ exists on TiO₂, according to XPS. It is concluded that vanadia loaded on Ti-rich TiO₂-SiO₂ with low SiO₂ 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 SO₂ oxidation performance.     

Combined effect of H2O and SO2 on V2O5/AC catalysts for NO reduction with ammonia at lower temperatures

Combined effect of H₂O and SO₂ on V₂O₅/AC the activity of catalyst for selective catalytic reduction (SCR) of NO with NH₃ at lower temperatures was studied. In the absence of SO₂, H₂O inhibits the catalytic activity, which may be attributed to competitive adsorption of H₂O and reactants (NO and/or NH₃). Although SO₂ promotes the SCR activity of the V₂O₅/AC catalyst in the absence of H₂O, it speeds the deactivation of the catalyst in the presence of H₂O. The dual effect of SO₂ is attributed to the SO₄²⁻ formed on the catalyst surface, which stays as ammonium-sulfate salts on the catalyst surface. In the absence of H₂O, a small amount of ammonium-sulfate salts deposits on the surface of the catalyst, which promote the SCR activity; in the presence of H₂O, however, the deposition rate of ammonium-sulfate salts is much greater, which results in blocking of the catalyst pores and deactivates the catalyst. Decreasing V₂O₅ 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.     

低温选择性催化还原催化剂二氧化硫中毒及再生特性

采用液相共沉淀法制备Mn-Ce/TiO₂低温选择性催化还原催化剂,催化剂在120 ℃无二氧化硫条件下低温SCR活性高,NO转化率为92%。利用BET、SEM、TEM、XRD和XPS等技术对催化剂的二氧化硫中毒特性进行分析,结果表明,催化剂中毒是由于(NH₄)₂SO₃和(NH₄)₂SO₄在催化剂表面发生沉积,采用水洗、加热和还原气体保护加热等方式对催化剂进行再生实验,发现水洗对催化剂活性再生非常有效,特别是在水洗浸泡过程中采用超声波震荡。用离子色谱技术对水洗副产物进行分析,发现水洗液中主要离子为NO₃^-、SO₄^2--和NH₄^+。     

负载型Mn-Fe/γ-Al2O3低温脱硝催化剂的性能

采用共沉淀法制备了负载型Mn-Fe/γ-Al₂O₃低温SCR催化剂,运用固定床催化反应器,以氨气为还原剂,考察了负载量、活性组分配比、焙烧温度等制备条件和空速、O₂体积分数、NH₃/NO摩尔比等操作条件对Mn-Fe/γ-Al₂O₃催化剂低温脱硝性能的影响,并通过X射线衍射仪(XRD)、比表面积测定仪(BET)等手段对催化剂进行表征.结果表明,负载质量分数为20%、n(Mn):n(Fe)=4:1、焙烧温度为600℃、空速为16000h^-1、O₂体积分数为4%、NH₃/NO摩尔比为1.2、反应温度为200℃的条件下,NO转化率达到了96%以上.     

含钛高炉渣制备SCR烟气脱硝催化剂

以含钛高炉渣为原料,稀硫酸为溶剂提取钛液,钛液经水解、高温焙烧后制得高比表面积的TiO₂,并以其为载体采用分步浸渍法制备了V₂O₅-WO₃/ TiO₂催化剂。优化了含钛高炉渣的酸解条件,对所得TiO₂进行了XRD、XRF、BET表征,用自制催化剂评价系统考察了所制备催化剂的脱硝性能及抗硫抗水性能。结果表明：H₂SO₄浓度40%、酸渣比1.5、酸解温度80℃、酸解时间3 h条件下,TiO₂浸出率可达90%,水解产物主要为锐钛型TiO₂,纯度达到74%,含有21.2%无定形SiO₂及少量其他杂质。SiO₂的存在提高了产物的比表面积、孔径,有利于活性组分的负载。以含钛高炉渣基TiO₂为原料制备的V₂O₅-WO₃/TiO₂脱硝催化剂相比于以商业TiO₂和TiOSO₄制备的催化剂,在250～450℃具有更高的催化活性,且在300℃具有较好的抗硫抗水性能。     

Catalytic activation of ceramic filter elements for combined particle separation, NOx removal and VOC total oxidation

The development of a catalytically active filter element for combined particle separation and NO_x removal or VOC total oxidation, respectively, is presented. For NO_x removal by selective catalytic reduction (SCR) a catalytic coating based on a TiO₂–V₂O₅–WO₃ catalyst system was developed on a ceramic filter element. Different TiO₂ sols of tailor-made mean particle size between 40 and 190 nm were prepared by the sol–gel process and used for the impregnation of filter element cylinders by the incipient wetness technique. The obtained TiO₂-impregnated sintered filter element cylinders exhibit BET surface areas in the range between 0.5 and 1.3 m²/g. Selected TiO₂-impregnated filter element cylinders of high BET surface area were catalytically activated by impregnation with a V₂O₅ and WO₃ precursor solution. The obtained catalytic filter element cylinders show high SCR activity leading to 96% NO conversion at 300 °C, a filtration velocity of 2 cm/s and an NO inlet concentration of 500 vol.-ppm. The corresponding differential pressures fulfill the requirements for typical hot gas filtration applications. For VOC total oxidation, a TiO₂-impregnated filter element support was catalytically activated with a Pt/V₂O₅ system. Complete oxidation of propene with 100% selectivity to CO₂ was achieved at 300 °C, a filtration velocity of 2 cm/s and a propene inlet concentration of 300 vol.-ppm.     

Co3O4 based catalysts for NO oxidation and NOx reduction in fast SCR process

Reaction activities of several developed catalysts for NO oxidation and NO_x (NO + NO₂) reduction have been determined in a fixed bed differential reactor. Among all the catalysts tested, Co₃O₄ 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 Co₃O₄ catalyst, the effects of calcination temperatures, SO₂ concentration, optimum SV for 50% conversion of NO to NO₂ were determined. Also, Co₃O₄ based catalysts (Co₃O₄-WO₃) 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, N₂O formation over Co₃O₄-WO₃ catalyst is far less than that over the other catalysts but the standard SCR produces high concentration of N₂O over all the catalysts. The effect of SO₂ concentration on NO_x reduction is found to be almost negligible may be due to the presence of WO₃ that resists SO₂ oxidation.