Effect of TiO2 surface properties on the SCR activity of NOx emission abatement catalyst

NOx emission abatement catalysts V2O5 supported on various TiO2 including anatase, rutile and mixture of both were investigated with various physico-chemical measurements such as BET, NH3-TPD, NARP, XRD and so on, and the effect of TiO2 surface properties on the SCR (selective catalytic reduction) activity of V20s/TiO2 catalysts was studied. It was found that the TiO2 surface properties had strong affect on the SCR activity of V2Os/TiO2 catalysts. The stronger acidic property resulted in the higher exposure of active sites as well as the higher SCR activity.     

钒钛基SCR催化剂中毒及再生研究进展

在烟气脱硝系统中,选择性催化还原催化剂的中毒和再生是广泛关注的问题。文章介绍了钒钛基催化剂的碱金属中毒、碱土金属中毒、砷中毒和二氧化硫中毒,探讨其成因,并对中毒机理进行了分析,同时研究了避免催化剂中毒的措施以及中毒催化剂的再生技术。对碱金属中毒和碱土金属中毒催化剂的水洗再生和硫酸酸洗再生方法进行了实验评价。文章对溶胶凝胶法制备的以陶瓷颗粒为骨架的纳米负载型催化剂V2O5-WO3/TiO2(C)进行研究。实验结果表明,硫酸酸洗再生对碱金属和碱土金属中毒催化剂具有较好的再生效果。在380～410℃温度范围内可使中毒催化剂的NO去除率恢复至90%以上。水洗再生对碱金属中毒催化剂无明显效果,而在380～410℃温度范围内可使碱土金属中毒催化剂的NO去除率达到80%以上。对V2O5-WO3/TiO2(C)抗SO2性能研究表明,以锐钛TiO2为载体的V2O5-WO3/TiO2(C)催化剂具有较好的抗SO2效果。     

蜂窝状SCR脱硝催化剂成型配方选择

通过对钒钛基蜂窝状SCR脱硝催化剂的制备工艺研究,探索了二氧化钛(TiO2)载体及成型剂配方对产品机械性能及脱硝活性的影响.分别选用工业级硫酸法锐钛型TiO2和进口商业纳米锐钛型TiO2为载体原料,所考察的主成型剂包括二氧化硅(SiO2),活性氧化铝(γ-Al2O3),以及SiO2和硼酸(H3BO3)的混合粉体.进一步对载体及所制备催化剂样品进行表征,机械强度及脱硝活性测试.结果表明,商业纳米级TiO2较工业级TiO2在杂质含量、粉体粒径、分散度等方面占有明显优势,但TiO2晶粒尺寸要高于后者,比表面积亦低于工业级样品.在SCR催化剂制备上,相对工业级TiO2而言商业纳米级TiO2制备样获得了较高的机械强度,但其在脱硝活性方面并不占有优势.而对主成型剂配方的探索显示,以SiO2与H3BO3按一定比例混合得到的成型剂配方不但能够显著提高蜂窝状催化剂的机械性能,另一方面也能够维持其较高的脱硝活性,因此该配方作为钒钛基SCR催化剂的成型剂是合理可行的.     

V-W/TiO_2/γ-Al_2O_3催化剂催化还原NO的研究

掺杂15%TiO2对γ-Al2O3改性制备了TiO2/γ-Al2O3复合氧化物载体,以此复合氧化物及TiO2、γ-Al2O3为载体用浸渍法负载钒钨制备了一系列催化剂,采用比表面积和孔结构分析、X射线衍射(XRD)、高分辨电镜(HRTEM)、原位红外(in situ FT-IR)等技术对载体和催化剂进行宏观-微观表征,同时在模拟氨气选择性催化还原NO(NH3-SCR)的反应条件下对催化剂的脱硝反应活性进行考察,比较研究TiO2掺杂对V2O5-WO3/TiO2和V2O5-WO3/γ-Al2O3催化剂的改性作用。结果发现,少量TiO2掺杂制得的TiO2/γ-Al2O3复合载体中,TiO2和γ-Al2O3之间的协同作用使得V2O5-WO3/TiO2/γ-Al2O3催化剂的选择性催化还原脱硝效率及活性窗口明显优于单一载体制备的催化剂,并表现出了良好的热稳定性;各种表征结果表明,TiO2/γ-Al2O3复合载体中TiO2高度分散在γ-Al2O3上,复合载体具有较大的比表面积,载体表面存在大量的Br?nsted酸位和较多的活性中间产物,这些可能是TiO2/γ-Al2O3复合载体催化剂具有较好SCR活性的原因。     

Iron-doped Mn-Ce/TiO2 catalyst for low temperature selective catalytic reduction of NO with NH3

The catalysts of iron-doped Mn-Ce/TiO 2(Fe-Mn-Ce/TiO 2) prepared by sol-gel method were investigated for low temperature selective catalytic reduction(SCR) of NO with NH 3.It was found that the NO conversion over Fe-Mn-Ce/TiO 2 was obviously improved after iron doping compared with that over Mn-Ce/TiO 2.Fe-Mn-Ce/TiO 2 with the molar ratio of Fe/Ti = 0.1 exhibited the highest activity.The results showed that 96.8% NO conversion was obtained over Fe(0.1)-Mn-Ce/TiO 2 at 180°C at a space velocity of 50,000 hr 1.Fe-Mn-Ce/TiO 2 exhibited much higher resistance to H 2 O and SO 2 than that of Mn-Ce/TiO 2.The properties of the catalysts were characterized using X-ray diffraction(XRD),N 2 adsorption,temperature programmed desorption(NH 3-TPD and NOx-TPD),and Xray photoelectron spectroscopy(XPS) techniques.BET,NH3-TPD and NOx-TPD results showed that the specific surface area and NH3 and NOx adsorption capacity of the catalysts increased with iron doping.It was known from XPS analysis that iron valence state on the surface of the catalysts were in Fe3+ state.The doping of iron enhanced the dispersion and oxidation state of Mn and Ce on the surface of the catalysts.The oxygen concentrations on the surface of the catalysts were found to increase after iron doping.Fe-Mn-Ce/TiO2 represented a promising catalyst for low temperature SCR of NO with NH3 in the presence of H2 O and SO2.     

V2O5/TiO2催化剂脱除NO的研究

采用了等体积浸渍法制备二氧化钛负载钒氧化物催化剂（V2O5/TiO2）,研究了V2O5负载量、反应温度、烟气流量、氨氮比以及运行时间各因素对NH3选择性催化还原NO反应（SCR）效率的影响.研究结果表明：经过500℃温度下煅烧,烟气流量为200ml/min,负载量为7wt％的V2O5/TiO2催化剂,在400℃温度下反应,NO脱除率可达70.5％.     

不同纳米级锐钛型TiO2的V2O5基催化剂脱氮性能

以2种不同纳米级锐钛型TiO2为载体负载V2O5和WO3制备得到脱氮催化剂H和Z,在自制固定床反应器中测试其DeNOx活性,结果表明,催化剂H的活性比催化剂Z低得多.利用XRD、BET、FT-IR和SEM等手段对2种催化剂进行比较,BET表面积虽然会对DeNOx活性产生一定的影响,但催化剂H主要因为活性物质V2O5和载体TiO2发生反应,生成V3Ti6O17,导致其DeNOx活性大幅下降,而在催化剂Z中TiO2仍然保持锐钛型,未与V2O5发生反应.     

超声波浸渍法制备V_2O_5-WO_3/TiO_2选择性催化还原脱硝催化剂

采用超声波浸渍法、传统浸渍法制备一系列V2O5-WO3/TiO2催化剂,对催化剂的反应活性进行考察。研究表明:与普通浸渍法相比,超声波浸渍法可以提高催化剂的脱硝效率,拓宽催化反应的温度窗口。超声波浸渍时间和超声波功率对催化剂的反应活性有较大影响。浸渍时间增加,催化剂脱硝效率也随之提高。超声波功率增加,催化剂的脱硝效率先提高后降低。在超声波频率28 kHz,超声波功率400 W,超声作用时间1.5 h,超声水粉比为100 mL H2O/10 g TiO2的条件下,制得的V2O5-WO3/TiO2脱硝催化剂脱硝效率接近100%。通过SEM对制备的催化剂进行表征,超声波浸渍法制备的催化剂的活性成分在载体上分散更加均匀。     

钒和钨负载量对V2O5-WO3/TiO2表面形态及催化性能的影响

采用浸渍法制备了一系列不同钒和钨负载量的V₂O₅-WO₃/TiO₂催化剂样品,对样品NH₃选择性催化还原NO性能进行了评价,并用BET、XRD、XPS等手段对催化剂样品的表面形态进行了表征.研究发现,钒的负载量对催化剂的比表面积和催化活性有显著影响,当钒负载量从1％升高到8％时,催化剂比表面积下降了16 m²/g,最高活性温度降低了约100℃.钨起到稳定剂和助剂的双重作用,当钒负载量为1％时,钨负载量从0升高到6％,催化剂比表面积仅下降了3 m²/g,而活性温度窗口向高温和低温各拓宽了约50℃.研究表明钒和钨负载量都能影响催化剂表面的VO_x物种,但对催化剂的表面晶型没有明显影响.     

NH3-SCR performance and the resistance to SO2 for Nb doped vanadium based catalyst at low temperatures

Niobium oxide as the promoter was doped in the V/WTi catalyst for the selective catalytic reduction(SCR)of NO.The results showed that the addition of Nb_2O_5could improve the SCR activity at low temperatures and the 6 wt.%additive was an appropriate dosage.The enhanced reaction activity of adsorbed ammonia species and the improved dispersion of vanadium oxide might be the reasons for the elevation of SCR activity at low temperatures.The resistances to SO_2of 3V6Nb/WTi catalyst at different temperatures were investigated.FTIR spectrum and TG-FTIR result indicated that the deposition of ammonium sulfate species was the main deactivation reason at low temperatures,which still exhibited the reactivity with NO above 200°C on the catalyst surface.There was a synergistic effect among NH_3,H_2O and SO_2that NH_3and H_2O both accelerated the catalyst deactivation in the presence of SO_2at 175°C.The thermal treatment at 400°C could regenerate the deactivated catalyst and get SCR activity recovered.The particle and monolith catalysts both kept stable NO_xconversion at 225°C with high concentration of H_2O and SO_2during the long time tests.     

添加硫酸根对燃煤电厂V2O5基脱硝催化剂性能的影响

采用浸渍法分别制得活性物质V2O5的含量均为1%和SO2-4的含量不同的催化剂,并通过实验研究了添加SO-24对燃煤电厂SCR法脱硝技术中V2O5基催化剂活性和热稳定性的影响.在固定床反应器上,在NH3/NOx物质的量比为1.0和模拟烟气流量为72 L·h-1条件下,对几种催化剂的活性进行了测试,结果显示,当负载加入5.01%的SO2-4或使用含有8.91%的SO-24载体制备催化剂时,催化剂的活性提高最为显著;在TGA 92热重.差热分析仪上对这两种催化剂进行了热重实验,结果表明,添加的硫酸根对催化剂的热稳定性也有一定提高,且不会影响电厂SCR催化剂的使用.     

V2O5/TiO2催化剂用于烟气同时脱硫脱硝的研究

研究了用V2O5/TiO2催化剂同时脱除烟气中的SO2和NO,考察了H2还原温度及其它反应条件对SO2和NO脱除率的影响。结果表明,经H2还原后所制得的V2O5/TiO2催化剂可以提高脱硫脱硝活性,最佳还原温度为700℃;在450～500℃的烟气温度范围内,该催化剂有较佳的脱硫脱硝活性;在相同反应温度下,空速越大,SO2和NO的脱除率越低;烟气中的氧气可大大提高V2O5/TiO2的脱硫脱硝活性,且氧气体积含量在5%～10%范围内变化时,对SO2和NO脱除率的影响较小。     

Mn-Ce-Co/TiO2催化剂低温脱硝活性研究

以纳米TiO2为载体,通过浸渍法制备一系列改性Mn-Ce/TiO2脱硝催化剂.通过实验考察不同元素组分催化剂的脱硝活性,同时探讨金属氧化物掺杂对提高催化剂低温脱硝活性的机理.活性测试结果显示,Co掺杂能最有效地提高Mn-Ce/TiO2催化剂在低温段的SCR脱硝活性,在n(Co):n(TiO2)=0.08～0.10、体积空速为35100h-1的条件下,催化剂在120℃时就能达到80%以上的NO去除率,140℃左右时的NO去除率接近100%.BET、XRD、TPR、TPD等表征测试结果表明,Co掺杂可改进Mn-Ce/TiO2催化剂的物化特性,增加催化剂表面的活性酸位点及活性氧数量,提高催化剂的氧化还原能力,从而提高Mn-Ce/TiO2催化剂低温SCR脱硝活性.     

Photocatalytic performance of TiO2 catalysts modified by H3PW12O40, ZrO2 and CeO2

The binary composite photo-catalysts CeO2/TiO2, ZrO2/TiO2 and the ternary composite photo-catalysts H3PW12O40-CeO2/TiO2,H2PW12O40-ZrO2/TiO2 were prepared by sol-gel method. The catalysts were characterized by thermogravimetric-differential thermal analysis (TG-DTA), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The photocatalyfic elimination of methanol was used as model reaction to evaluate the photocatalytic activity of the composite catalysts under ultraviolet light irradiation. The effects of doped content, activation temperature, time, initial concentration of methanol and gas flow rate on the catalytic activity were investigated. The results showed that after doping a certain amount of CeO2 and ZrO2, crystaniTation process of TiO2 was restrained, particles of catalysts are smaller and more uniform. Doping ZrO2 not only significantly improved the catalytic activity, but also increased thermal stability. Doping H3PW12O40 also enhanced the catalytic activity. The catalytic activities of binary and ternary composite photocatalysts were significantly higher than tin-doped TiO2. The dynamics law of photocatalytic reaction over the binary CeO2/TiO2 and ZrO2/TiO2 catalysts has been studied. The activation energy 15.627 and 15.631 kJ/mol and pre-exponential factors 0.5176 and 0.9899 s-1 over each corresponding catalyst were obtained. This reaction accords to the first order dynamics law.     

MnOx/TiO2-ZrO2催化剂的制备及低温催化还原NO的研究

采用共沉淀法制备了TiO2-ZrO2复合氧化物,以其为载体采用等体积浸渍法制备了不同负载量的MnOx/Ti02-Zr02催化剂.低温下以NH3为还原剂考察了催化剂选择性催化还原(SCR)NO的活性.借助N2吸附、XRD、热重-差示扫描量热法(TG-DSC)对催化剂进行微观表征和分析.结果表明,负载量为5%时,生成的MnO2高度分散,NO的转化率较高;负载量为10%和15%时,出现MnO2晶相,NO的转化率有所下降.120-240℃、体积空速为10000 h-1的条件下,3种负载量的催化剂上NO转化率均大于90%.     

Performance and mechanism study for low-temperature SCR of NO with propylene in excess oxygen over Pt/TiO2 catalyst

A 0.5 wt.% Pt/TiO2 catalyst was prepared and used for the low-temperature selective catalytic reduction(SCR) of NO with C3 H6 in the presence of excess oxygen.The effects of Pt loading and O2 concentration on Pt/TiO2 catalytic performance for low-temperature SCR were investigated.It was found that optimal Pt loading was 0.5 wt.% and excess O2 favored low-temperature SCR of NOx.The mechanism of low-temperature SCR of NO with C3 H6 was investigated with respect to the behavior of adsorbed species over Pt/TiO2 at 150°C using in situ DRIFTS.The results indicated that surface nitrosyl species(Pt δ+-NO and Ti 3+-NO) and Pt 2+-CO are main reaction intermediates during the interactions of NO,C3 H6 and O2.A simplified NO decomposition mechanism for the low-temperature SCR of NO with C3 H6 was proposed.     

V2O5/TiO2催化剂中毒机理的试验研究

选择性催化还原(SCR)催化剂是SCR烟气脱硝技术的核心,是整个SCR系统脱硝效率和经济性的决定因素.本文工作的主要研究思路是以钒钛SCR催化剂为研究对象,研究了H2O和SO2,以及相同含量下K、Na、Ca、Pb的氧化物对钒钛催化剂NO转化率的影响.H2O的存在会抑制V2O5/TiO2催化剂脱硝活性,而SO2在一定程度上促进(V2O5/TiO2)催化剂的SCR脱硝反应,提高NO转化率;碱金属K对钒钛催化剂的钝化作用都是最强,K2O和Na2O的掺入会抑制钒钛催化剂上V2O5的还原能力,而CaO和PbO的掺入对钒钛催化剂上V2O5的还原能力影响较小.     

焙烧温度对CeO_2(ZrO_2)/TiO_2选择性催化脱硝性能的影响

采用溶胶-凝胶法并以不同温度焙烧制备一系列CeO_2(ZrO_2)/TiO_2(CZT)催化剂,考察了CZT催化剂固相结构、酸量、比表面积等性能与催化活性的关系。采用XRD、BET、NH3-TPD、H2-TPR以及XPS等表征技术对催化剂进行表征。结果表明:焙烧温度为450℃时CZT催化剂具有最高的催化活性,其在240~400℃的温度窗口内活性均高于90%,且具有较好的抗水和抗硫中毒能力。随着焙烧温度的提高,催化剂表面的Ce和Zr原子进入体相晶格且Ce0.5Zr0.5O2向Ce0.75Zr0.25O2转变,导致催化剂的储释氧能力和氧化还原性能降低。另外,锐钛矿和金红石型TiO_2晶粒尺寸的增加,催化剂的有效比表面积和总酸量降低,因此CZT催化活性随着焙烧温度的提高而有所降低。换言之,大的比表面积、良好的氧化还原性能、表面Ce4+的富集以及酸性位的增多均有利于NH3-SCR活性的提高。     

Effect of MoO3 on vanadium based catalysts for the selective catalytic reduction of NOx with NH3 at low temperature

The selective catalytic reduction(SCR) activities of the MoO_3 doped V/WTi catalysts prepared by the incipient wetness impregnation method at low temperature were investigated.The results showed that the addition of MoO_3 could enhance the NO_ xconversion at low temperature and the best SCR activity was obtained when the dosage of MoO_3 reached5 wt.%. The NH3-TPD and DRIFTS experiments indicated that the addition of MoO_3 changed the type and number of acid sites on the surface of catalysts and reaction activities of acid sites were altered at the same time. The redox capacity and amount of active oxygen species got improved for V3Mo5/WTi catalyst, which could be confirmed by the H_2-TPR and transient response experiments. Water vapor inhibited the NO_xconversion at low temperature. Deposition of ammonium sulfate or bisulfate might be main reason for the loss of catalytic activity in the presence of SO_2 at low temperature. Choosing the suitable NH_3/NO ratio and elevation of reaction temperature both could weaken the influence of SO_2 on the SCR activity of the V3Mo5/WTi catalyst. Thermal treatment of the deactivated catalyst at350°C could get the low temperature activity recovered. The decrease of GHSV improved the de NO_x efficiency at low temperature and we speculated that the rational technological process and operation parameters could contribute to the application of this kind of catalysts in real industrial environment.     

纳米TiO_2-Al_2O_3负载CuMnO_x对甲苯的催化燃烧

研究采用改进的溶胶-凝胶法制备了TiO2-Al2O3复合载体,并用浸渍法制备CuMnOX/TiO2-Al2O3催化剂,通过对甲苯废气催化燃烧的实验,分别考察了Cu-Mn负载量、Cu/Mn摩尔比、焙烧温度及载体对催化剂制备过程及催化剂活性的影响。实验结果表明:活性组分负载量25%,铜锰活性组分的配比Cu:Mn=1:2,焙烧温度500℃是浸渍法制备CuMnOX/TiO2-Al2O3催化剂较佳的工艺条件;XRD衍射图谱表明,500℃下铜锰尖晶石的存在是催化剂催化活性优良的主要原因;由复合载体制备的CuMnOX/TiO2-Al2O3催化剂比单一载体制备的CuMnOX/Al2O3催化剂具有更高的甲苯转化率,其T99比单一载体要低20℃以上。