Ce^(4+),Zr^(4+)共掺杂提高V_2O_5-WO_3/TiO_2催化剂脱硝性能及抗K中毒能力（英文）

近年来, NO_x的排放造成了严重的环境污染.氨选择性催化还原技术(NH3-SCR)是目前消除NO_x最有效的手段之一.V_2O_5-WO_3/TiO_2催化剂在300–400°C范围内表现出优异的脱硝性能,因此被广泛用于NH3-SCR反应.然而该催化剂抗碱(土)金属中毒性能较差,且碱(土)金属碱性越强对催化剂的毒害越大(即K> Na> Ca> Mg).已有研究显示,当K_2O质量分数达1%时,催化剂将完全失活,所以对传统的V_2O_5-WO_3/TiO_2催化剂进行改性以提高其抗K中毒性能具有十分重要的意义.最近, CeO_2由于具有优异的氧化还原性能和储/释氧能力,在NH3-SCR反应得到了广泛的关注.研究显示, CeO_2的改性可提高钒基催化剂脱硝活性及抗碱金属中毒性能,这主要是由于CeO_2的掺杂可以有效提高催化剂表面酸性及氧化还原能力. ZrO_2是一种酸碱两性氧化物,常被用作载体或者助剂.研究显示, ZrO_2的引入可以提高催化剂热稳定性,增大比表面积以及提高氧迁移能力.基于此,我们制备了一系列的V_2O_5-WO_3/TiO_2-ZrO_2, V_2O_5-WO_3/TiO_2-CeO_2以及V_2O_5-WO_3/TiO_2-CeO_2-ZrO_2催化剂,以期提高V_2O_5-WO_3/TiO_2催化剂脱硝性能及抗K中毒能力.研究发现, Ce^(4+), Zr^(4+)共掺杂可以有效提高V_2O_5-WO_3/TiO_2催化活性,拓宽反应温度窗口,增强抗K中毒能力.进一步借助X射线衍射、比表面积测定、氨气-程序升温脱附、氢气-程序升温还原和X射线光电子能谱等表征对催化剂进行全面分析.结果显示, Ce^(4+), Zr^(4+)共掺杂对V_2O_5-WO_3/TiO_2催化剂物理化学性质的影响与其脱硝性能及抗K中毒能力有着密不可分的关系.首先, Ce^(4+), Zr^(4+)可以掺杂进入TiO_2晶格,抑制TiO_2晶粒的生长,从而导致比表面积以及总孔体积的增加;比表面积的增加有利于活性物种的分散,而总孔体积的增加有利于反应物分子与催化剂充分接触.其次, Ce^(4+), Zr^(4+)共掺杂可以提高催化剂表面酸性和氧化还原性能,表面酸性的增加有利于催化剂吸附与活化反应物种NH_3,氧化还原性能的提高有利于NO氧化为NO_2,进而通过"快速NH3-SCR"反应提高催化剂活性;同时, Ce^(4+), Zr^(4+)共掺杂还可以有效降低K中毒对表面酸性和氧化还原性能的影响,这主要是由于Ce^(4+)可以与K原子结合形成Ce-O-K物种,而Zr^(4+)的引入可以增加Ce^(4+)的热稳定性,使得更多的Ce^(4+)与K结合,避免了K与活性钒物种结合形成V-O-K物种,使得活性V5+得到了有效的保护.原位红外实验揭示了V_2O_5-WO_3/TiO_2-CeO_2-ZrO_2催化反应遵循L-H机理,且K中毒并未改变其反应机理.最后,该催化剂在H_2O和SO_2存在的条件下仍具有最佳的脱硝性能,因而有望用于实际高K含量的燃煤烟气脱硝.

CeO_2表面分散态WO_3的氨选择性催化还原性能（英文）

铈基材料在氨选择性催化还原氮氧化物(NH_3-SCR)的研究中备受关注,亦被认为是潜在的新型环境友好型催化剂.CeO_2具有独特的氧化还原性能和优良的储释氧性能,易与其它金属氧化物发生协同催化而有利于提高催化剂的催化反应性能,而WO_3可以改善催化剂的表面酸性.研究亦报道了WO_3可以改善CeO_2的NH_3-SCR反应的高温活性和N2选择性,其原因在于WO_3增加了铈基催化剂NH_3的吸附性能且抑制了NH_3非选择性氧化成NOx.我们采用浸渍法制备了一系列负载型WO_3/CeO_2催化剂,并利用XRD,Raman,XPS,H2-TPR,NH_3-TPD和in situ DRIFT对其理化性质进行了表征,系统研究了WO_3负载量对WO_3/CeO_2催化剂NH_3-SCR催化性能的影响,主要研究的内容包括:(1)WO_3/CeO_2催化剂中WO_3的状态与催化性能之间的关系;(2)WO_3负载量对WO_3/CeO_2催化剂的NH_3和NO吸附行为的影响.NH_3-SCR反应测试表明WO_3负载量对WO_3/CeO_2催化剂有显著影响,优化的WO_3/CeO_2催化剂在200–450°C具有良好的脱硝性能,且在300°C通入SO2+H2O条件下依然保持优异的催化活性.XPS和H2-TPR结果表明,WO_3分散在CeO_2表面抑制了CeO_2表面活性氧和表面晶格氧的氧化能力,这导致催化剂对NO的氧化以及对硝酸盐的吸附性能相比于纯CeO_2显著降低,同时,in situ DRIFT也证实,随着WO_3负载量的增加,WO_3/CeO_2催化剂表面吸附硝酸盐能力下降.因此,我们认为,由于低活性的晶相WO_3覆盖在催化剂表面,阻碍了催化剂的表面活性位,降低了催化剂的氧化还原能力和表面酸量,从而晶相WO_3抑制了WO_3/CeO_2催化剂的催化活性.同时,我们发现在70°C下采用氨水可以洗掉WO_3/CeO_2催化剂中的晶相WO_3,且洗涤后的样品催化活性有所提升,这进一步验证了晶相WO_3对催化活性的抑制作用.In situ DRIFT结果表明WO_3/CeO_2催化剂上NH_3-SCR反应是通过Eley-Rideal机理进行,即吸附NH_3物种与气相NO之间发生反应.随着WO_3负载量的增加,WO_3/CeO_2催化剂中NH_3的吸附能力先增强后减弱,而NO吸附能力持续减弱,这有利于表面酸位在反应过程中不被硝酸盐阻碍,当WO_3负载量在分散容量附近时,这种吸附特性的效果发挥到最大,从而最大限度地促进NH_3-SCR反应按照Eley-Rideal机理顺利进行.

表面Mo修饰提高CeTiO_x催化剂低温脱硝性能（英文）

近年来,以雾霾为代表的大气污染问题严重影响到经济社会的可持续发展.其中,氮氧化物(NOx)的大量排放是导致雾霾天气的重要原因之一.氨选择性催化还原(NH3-SCR)是目前消除氮氧化物的主流技术,低温NH3-SCR更是广泛应用于钢铁、焦化、水泥、玻璃、陶瓷和垃圾焚烧等行业的烟气排放治理.传统的V2O5-WO3/Ti O2催化剂活性温度高(300–400 oC)且钒具有生物毒性,因此亟待开发环境友好的低温非钒基脱硝催化剂.最近, Ce Ti Ox基催化剂由于在中高温段(250–400 oC)表现出优异的脱硝性能而得到广泛关注.然而,该催化剂仍面临低温活性差及抗硫性能差的问题,制约了其工业化应用.研究显示,添加过渡金属可提高Ce Ti Ox基催化剂的脱硝活性和抗硫中毒性能,这主要是因为过渡金属的添加可以有效改善催化剂的氧化还原性能和表面酸性.Mo O3作为一种可以提供大量酸性位的氧化物,常被用作助剂改善钒钨钛催化剂的活性.研究显示, Mo O3的引入可以促进催化剂中钒物种的分散度以及提高表面酸性.基于此,我们制备了一系列不同Mo含量的Mo O3/Ce Ti Ox催化剂,以期提高Ce Ti Ox催化剂的低温脱硝性能及抗SO2中毒能力,并着重研究表面Mo的修饰对Ce Ti Ox催化剂物理化学性质的影响.研究发现,表面Mo修饰可以显著提高Ce Ti Ox的低温催化活性,其脱硝效率在150 oC即可达到80%,同时抗SO2中毒能力也得到增强.进一步借助X射线衍射、比表面积测定、氢气程序升温还原、氨气程序升温脱附和X射线光电子能谱等方法对催化剂进行了全面表征分析.结果显示,表面Mo修饰对Ce Ti Ox催化剂物理化学性质的影响与其脱硝性能有着密不可分的关系.首先,钼物种主要是以Mo O3的形式存在于Ce Ti Ox表面,其最佳的负载量为4wt.%.其次,表面Mo的沉积显著提高了催化剂的表面酸量,尤其是Br?nsted酸位的数量,而表面酸位的增加有利于催化剂吸附与活化反应物种NH3;同时,表面Mo修饰还减弱了硝酸盐在催化剂表面的吸附,进一步促使NH3-SCR反应按照Eley-Rideal机理顺利进行.最后,该催化剂在H2O和SO2存在的条件下仍具有最佳的脱硝性能,因而有望用于实际含SO2的低温烟气脱硝.

Mo的引入方式对CeO_(2)脱硝性能的影响

固定源排放的氮氧化物(NOx)导致了严重的环境污染问题,NH_(3)选择性催化还原(NH_(3)-SCR)被认为是目前控制NOx排放的最有效技术,已广泛应用于电力行业的烟气排放治理.然而,我国非电行业的NOx减排仍然面临着重大挑战,因为其排放的废气温度通常低于300℃,且含有一定量的SO_(2),传统的钒基SCR催化剂因活性温度(300~400℃)较高而无法有效发挥作用.因此,亟待开发新型的高效低温SCR催化剂.铈基催化剂由于氧化铈(CeO_(2))的优异储氧能力(OSC)和良好的氧化还原能力而显示出较好的低温(80~300℃)脱硝性能,如Mn-Ce,W-Ce,Ta-Ce,Cu-Ce和Nb-Ce等.但这些铈基催化剂易被烟气中的SO_(2)毒化而导致催化活性降低.因此,提高铈基SCR催化剂抗硫中毒能力是其产业化应用的关键.已有研究发现,通过构筑结构保护层或添加另一种金属来保护活性组分是提高SCR催化剂抗硫性能的一种可行策略.氧化钼(MoO3)通常被用做传统V_(2)O_(5)/TiO_(2)催化剂的促进剂以提高其水热稳定性和表面酸性.研究表明,在V/Ti催化剂中引入钼物种不仅可以提高其SCR活性,而且提高了V/Ti催化剂的抗SO_(2)性能,这是由于VMo/Ti表面较少的V‒O‒V键削弱了对SO_(2)的氧化作用.Tang等开发了一种Fe_(2)O_(3)/MoO3纳米片催化剂,显示出比纯Fe_(2)O_(3)更好的抗SO_(2)能力,主要是由于层状结构的MoO3能阻止NH4+在硫酸氢铵中的沉积.目前关于Mo的引入方式即催化剂的制备方法对铈基催化剂物化性能和NH_(3)-SCR催化性能(特别是抗SO_(2)能力)的影响的研究还比较少.本文分别采用浸渍法和沉淀法在CeO_(2)中引入钼物种,制备了Mo-CeO_(2)和MoCe-cp催化剂来探究制备方法对MoCe催化剂的脱硝性能及抗SO_(2)中毒能力的影响.结果表明,引入Mo可以显著地提高CeO_(2)的低温脱硝性能,其中Mo-CeO_(2)催化剂在150℃即可达到80%以上的脱硝效率,同时抗SO_(2)中毒性能也得到了显著提高.对催化剂结构、氧化还原能力、表面酸度和反应物分子的吸附脱附性质进行了表征,并与MoCe催化剂脱硝性能和抗硫性能相关联.结果表明,Mo-CeO_(2)和MoCe-cp催化剂的物理化学性质和脱硝性能有明显区别.首先,Mo-CeO_(2)中的钼物种主要存在于CeO_(2)表面,而MoCe-cp中的钼物种主要存在于CeO_(2)体相,其为Mo-CeO_(2)表面带来大量的Brönsted酸位并抑制了硝酸盐的吸附,促使NH_(3)-SCR反应按照Eley-Rideal机理进行,进而表现出优于MoCe-cp的低温活性.其次,Mo-CeO_(2)表面更多的Mo物种抑制了SO_(2)的吸附,从而使Mo-CeO_(2)表现出更好的抗SO_(2)性能.本文为具有实际应用前景的铈基NH_(3)-SCR催化剂的设计提供了参考.

Promotion effect of bulk sulfates over CeO_(2)for selective catalytic reduction of NO by NH_(3)at high temperatures

Understanding the influence of sulfates over catalysts for selective catalytic reduction of NO with NH_(3)(NH_(3)-SCR)is crucial due to the universal presence of SO_(2)in exhaust gas.Depending on the degree of sulfation,there mainly exist surface and bulk sulfates and NH_(3)-SCR activity is generally considered to suffer more from bulk sulfates.Herein,the unique function of bulk sulfates over Ce O_(2)in promoting hightemperature SCR reaction is revealed.Notably,compared with CeO_(2)dominated with surface sulfates(S-CeO_(2)-4h)and commercial V_2O_5-WO_(3)/TiO_(2),CeO_(2)with bulk sulfates(S-Ce O_(2)-72h)exhibits admirable NO conversion at the temperature range of 400-550℃.Bulk sulfates provide more Br?nsted acid sites with stronger strength for NH_(3)adsorption.Moreover,the oxidation ability of Ce O_(2)is significantly inhibited due to electron-withdrawing effect from bulk sulfates,which alleviates NH_(3)oxidation at high temperatures.More NH_(3)adsorption with high stability and limited NH_(3)oxidation capacity ensure the excellent catalytic performance for S-CeO_(2)-72h in high-temperature denitration.This work provides new insight of bulk sulfates in promoting SCR activity and open a new avenue to design de NO_xcatalysts employed at high temperatures.

Highly selective catalytic reduction of NO_x by MnO_x–CeO_2–Al_2O_3 catalysts prepared by self-propagating high-temperature synthesis

We first present preparation of MnOx–CeO_2–Al_2O_3 catalysts with varying Mn contents through a self-propagating high-temperature synthesis(SHS) method, and studied the application of these catalysts to the selective catalytic reduction of NOxwith NH3(NH_3-SCR).Using the catalyst with 18 wt.% Mn(18 MnCe1Al2), 100% NO conversion was achieved at 200°C and a gas hourly space velocity of 15384 hr-1, and the high-efficiency SCR temperature window, where NO conversion is greater than 90%, was widened to a temperature range of 150–300°C. 18 MnCe1Al2 showed great resistance to SO_2(100 ppm)and H_2O(5%) at 200°C. The catalysts were characterized using X-ray diffraction, X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller(BET) analysis, scanning electron microscopy, Fourier transform infrared spectroscopy, and H_2 temperature programmed reduction. The characterization results showed that the surface atomic concentration of Mn increased with increasing Mn content, which led to synergism between Mn and Ce and improved the activity in the SCR reaction. 18 MnCe1Al2 has an extensive pore structure,with a BET surface area of approximately 135.4 m^2/g, a pore volume of approximately 0.16 cm^3/g, and an average pore diameter of approximately 4.6 nm. The SCR reaction on 18 MnCe1Al2 mainly followed the Eley-Rideal mechanism. The performances of the MnOx–CeO_2–Al_2O_3 catalysts were good, and because of the simplicity of the preparation process,the SHS method is applicable to their industrial-scale manufacture.

Influence of CeO2 loading on structure and catalytic activity for NH3-SCR over TiO2-supported CeO2

A series of supported CeO2/TiO2 catalysts were prepared to explore the influence of CeO2 loading on these catalysts for the selective catalytic reduction of NO3 by NH3(NH3-SCR).The catalysts were investigated in detail by means of XRD,Raman,H2-TPR,NH3-TPD,XPS,in situ DRIFTS,and NH3-SCR reaction.The activity of the catalyst is closely related to the content of CeO2.When the loading of CeO2 is near the dispersion capacity(1.16 mmol Ce4+/100 m^2 TiO2),the catalytic activity is better.This may be because that the dispersed CeO2 is the active species and the catalyst has appropriate redox property,along with the larger amounts of surface Ce content and surface adsorbed oxygen species.Finally,a possible reaction mechanism via the Langmuir-Hinshelwood(L-H)mechanism is tentatively proposed to further understand the NH3-SCR reaction.

Enhancing low-temperature NH_(3)-SCR performance of Fe-Mn/CeO_(2)catalyst by Al_(2)O_(3)modification

In the work,supported catalysts of FeO_(x) and MnO_(x) co-supported on aluminum-modified CeO_(2)was synthesized for low-temperature NH_(3)-selective catalytic reduction(NH_(3)-SCR)of NO.Impressively,the SCR activity of the obtained catalyst is markedly influenced by the adding amount of Al and the appropriate Ce/Al molar ratio is 1/2.The activity tests demonstrate that Fe-Mn/Ce1 Al2 catalyst shows over 90%NO conversion at 75-250℃and exhibits better SO_(2)resistance compared to Fe-Mn/CeO_(2).Fe-Mn/Ce1 Al2 shows the expected physicochemical characters of the ideal catalyst including the larger surface and increased active reaction active sites by controlling the amount of Al doping.Also,the better catalytic activity is well correlated with the present advantaged surface adsorption oxygen species,Mn^(4+)species,Ce^(3+)species and the enhanced reducibility of Fe-Mn/Ce1 Al2,which is superior to the Fe-Mn/CeO_(2)catalyst.More importantly,we further demonstrate that the amount and strength of surface acid sites are improved by Al-doping and more active intermediates(monodentate nitrate)is generated during NH_(3)-SCR reaction.This work provides certain insight into the rational creation of simple and practical denitration catalyst environmental purification.

Solid-phase impregnation promotes Ce doping in TiO_(2) for boosted denitration of CeO_(2)/TiO_(2) catalysts

CeO_(2)/TiO_(2)(denoted as Ce Ti) catalysts obtained by solid-phase impregnation behaved better in lowtemperature selective catalytic reduction of NO_(x)with NH_(3)(NH_(3)-SCR) than that by conventional wet impregnation.To explore the main factors for activity distinction,the texture property,CeO_(2)dispersion and structure changes of TiO_(2)were comprehensively analyzed.It was found that surface changes of TiO_(2)had a significant impact on the improved activity.From results of inductively coupled plasma atomic emission spectrometer (ICP-AES),diffuse reflectance UV-vis spectroscopy (UV-vis-DRS) and Raman,it was inferred that Ce ions were partially incorporated into TiO_(2)lattice,accompanied with the formation of defects and vacancies during solid-phase impregnation.Accordingly,Ce Ti catalysts from solid-phase impregnation exhibited superiority in adsorption and activation of reactants.Further result from monitoring the preparation process indicated that the evolved NO played an important role in promoting Ce doping through depriving oxygen atoms on TiO_(2)surface.The interaction between Ce and Ti was enhanced.The catalyst performed better in NH_(3)-SCR,especially at low temperature,which testified the solid-phase impregnation could be an effective method to modulate interface structure for designing efficient catalyst.

Quantitative discrimination of surface adsorbed NOx species on CeO_(2) via spectrophotometry for SCR denitration investigation

CeO_(2)-based catalysts are widely investigated for selective catalytic reduction(SCR)of NO with NH3.Interaction of NO/O_(2) with CeO_(2) generally produces two surface species,i.e.,nitrates and nitrites.However,the explicit quantification of these two species is still unresolved.Herein,we reported that spectrophotometry characterization was effective in determining surface adsorbed NOx species on CeO_(2) by measuring the corresponding ions(NO_(2)-and NO_(3)^(-))dissolved in aqueous solution.Experimental results show that both nitrate(-NO_(3))and nitrite(-NO_(2))species can be quantitatively evaluated and the accuracy is verified by calibrating with NOx-TPD result.Exclusive transfer of adsorbed NOx from catalyst surface to aqueous solution is confirmed and the dissolution process can be accelerated by ultrasonic treatment.Moreover,useful information related to evolution of surface NOx species under various conditions(O_(2) treatment,different adsorption temperature and duration)and over different catalysts(Fe_(2)O_(3),MnO_(2) and MnOx—CeO_(2))are provided.The result of present study demonstrates the potential of spectrophotometry for quantitative discrimination of surface NOx species on CeO_(2) and other oxide-based materials,which is conducive to mechanism analysis of SCR reaction.