WO3对MnOx/TiO2低温脱硝SCR催化剂的改性研究

以醋酸锰为前驱物通过浸渍法制备了MnO_x/TiO₂催化剂,用WO₃对载体进行改性制得一系列MnO_x-WO₃/ TiO₂催化剂,采用X射线衍射（XRD）、比表面积测定(BET)、拉曼光谱(LRS)、原位红外(FT-IR)光谱等表征技术进行相关的微观表征分析,同时在模拟氨气选择性催化还原NO_x（NH₃-SCR）的反应条件下对催化剂的脱硝反应活性进行了考察。研究表明,添加5%的WO₃拓展了载体的比表面积,提高了催化剂的抗热性,增加了催化剂表面的Brnsted酸位,拓宽其选择性催化还原脱硝活性温度窗口,对MnO_x/TiO₂催化剂有很好的改性作用;先钨后锰的负载顺序优于先锰后钨;随着温度的升高,化学催化反应速率提高,催化剂表面NH₃吸附峰呈减弱或消失趋势,故催化剂脱硝活性温度曲线呈中间高、两头低。     

基于钛锡载体的SCR低温脱硝催化剂的表面性质研究

采用共沉淀法制备TiO₂-SnO₂固溶体,浸渍法负载CeO₂得到一系列xCeO₂/TiO₂-SnO₂负载型催化剂,在模拟NH₃选择性催化还原NO_x(NH₃-SCR)反应条件下考察催化剂低温脱硝活性。通过X射线衍射(XRD)、比表面积测定(BET)、程序升温还原(H₂-TPR)、程序升温脱附(NH₃-TPD)、高分辨率透射电子显微镜(HRTEM)、原位漫反射傅里叶变换红外光谱(in situ DRIFTS)等表征技术,研究了氧化铈负载后催化剂的微观结构、表面物种的存在状态、表面酸位等表面性质及NH₃吸附特性。结果表明,Ce:Ti物质的量比为0.1时,催化剂催化脱硝反应活性最高,同时具有较宽的温度窗口(250~300℃)和热稳定性;铈的过量负载会导致催化剂比表面积减小、活性窗口变窄,同时其氧化还原能力和NH₃吸附能力也减弱。NH₃-TPD结果显示,CeO₂的负载导致催化剂NH₃在弱酸及中等酸位的吸附显著增强,与催化剂NH₃-SCR最佳反应物温度降低有关。in situ DRIFTS表明,xCeO₂/TiO₂-SnO₂催化剂的Lewis酸位和Brønsted酸位强度均明显增强,同时,在1657~1666cm^-1处出现新的Brønsted酸位,参与SCR反应的主要物质是NH₄⁺分子。     

宽工作温度烟气脱硝催化剂制备及反应机理研究

以溶胶-凝胶法制备介孔TiO₂载体,采用分步浸渍法制备了V₂O₅-WO₃/TiO₂催化剂,借助BET、NH₃-TPD、H₂-TPR、SEM、活性评价、In-situ FT-IR等手段,考察了催化剂的结构、酸性、还原性、脱硝活性及反应机理等。介孔TiO₂载体比表面积为158.6 m²/g,制成催化剂后比表面积略有降低,约为136.7 m²/g。针对模拟烟气在φ_NH3/φ_NO=0.8的条件下测试催化剂的脱硝活性温度窗口为250~400 ℃,脱硝转化率达到80%。NH₃-TPD和H₂-TPR表征结果表明,催化剂在活性温度范围内具有典型的表面酸性位,载体TiO₂与V₂O₅之间存在的相互作用使得V₂O₅还原温度降低。利用In-situ FT-IR研究NH₃和NO在V₂O₅-WO₃/TiO₂催化剂表面吸附和氧化的反应过程发现,NH₃可同时吸附在L酸位和B酸位,NH₃在活性位上氧化脱氢形成NH₂物种是SCR脱硝反应的控制步骤。研究NO+O₂+NH₃反应时发现,吸附NH₃的催化剂引入NO和O₂后,共价吸附的NH₃首先消失。选择性催化还原反应发生在吸附态NH₃和气态或弱吸附态的NO之间,该反应遵从Eley-Rideal反应机理。     

Sm掺杂对Fe2O3催化剂NH3-SCR反应活性及抗水抗硫性作用

氮氧化物(NO_x)是主要的环境污染物之一,会造成酸雨、光化学烟雾和温室效应等环境问题.氨选择性催化还原(NH₃-SCR)技术是目前控制NO_x排放的最有效技术.其中,Fe₂O₃催化剂因其良好的抗硫性和低廉的成本而受到广泛关注,有望用作NO_x消除催化剂,但是它的低温还原性差、脱硝效率低等缺点限制了其应用.近期研究表明,钐掺杂金属氧化物可以调节其表面酸碱性及氧化还原性,可有效提高氧化物催化剂的脱硝效率和抗水抗硫性能.因此,将铁、钐二者优势结合,为合成一种低温、高效、环境友好型脱硝催化剂提供了可能.本文通过柠檬酸辅助的溶胶凝胶法合成了一系列钐均匀掺杂入Fe₂O₃纳米颗粒的复合氧化物脱硝催化剂,采用X射线光电子能谱(XPS),氢气程序升温还原(H2-TPR),氨气程序升温脱附(NH₃-TPD)以及原位漫反射红外光谱(in situ DRIFTS)等方法研究了钐的掺杂对铁基催化剂脱硝效率和抗水抗硫性的影响,旨在揭示催化剂表面物理化学性质和催化活性之间的关系.通过活性测试发现,钐的掺杂可以使Fe_0.94Sm_0.06O_x催化剂在175?325℃时实现>95%的脱硝效率和>93%的N2选择性.动力学测试研究表明,当基于催化剂的比表面积计算时,Fe_0.94Sm_0.06O_x催化剂的脱硝效率是纯Fe₂O₃催化剂的11倍;基于质量计算时则为37倍.此外,250℃时抗水抗硫测试结果显示,Fe_0.94Sm_0.06O_x催化剂可以在通入200×10^-6SO₂+5 vol%H₂O,空速为90000 h^-1时脱硝效率保持83%达168小时,并且在切断H₂O和SO₂后,该催化剂的脱硝效率可以很快完全恢复.XPS和H2-TPR结果表明,钐的掺杂使Fe_0.94Sm_0.06O_x催化剂的表面产生了大量的表面吸附氧,从而促进了NO的氧化以及快速NH₃-SCR反应的进行.NH₃-TPD与原位DRIFTS结果表明,钐的掺杂增强了催化剂的表面酸性,有效地提高了NH₃的吸附和活化能力,进而提高了催化剂的脱硝效率.另外,钐的掺杂还可以促使NH₄HSO₄在Fe_0.94Sm_0.06O_x催化剂表面较低温度下的分解,从而使催化剂具有很好的抗水抗硫性能.     

前驱体溶液pH值对V2O5-WO3/TiO2催化剂的低温NH3-SCR性能的影响

采用调节前驱体溶液pH值的方法制备了用于低温NH₃-SCR的V₂O₅-WO₃/TiO₂催化剂。通过XPS、Raman光谱、H₂-TPR、NH₃-TPD、NH₃-DRIFT、XRD及物理吸附等手段对催化剂进行了表征分析,并对其脱硝催化活性进行了测试。结果表明,前驱体溶液酸性的增强能够提高催化剂表面聚合态钒物种和V⁴⁺⁽³⁺⁾/V⁵⁺的比值以及表面酸性,增加活性位数量、降低反应的活化能、提高其脱硝催化性能。因此,通过提高前驱体溶液的酸性,有助于制备出脱硝活性较好的NH₃-SCR催化剂。     

微波辅助合成ZnO-TiO2及其可见光催化脱硝活性

通过对比水热溶胶凝胶法与微波辅助溶胶凝胶法制备的复合TiO₂的光催化性能,最终采用耗时较短且结晶度更好的微波辅助溶胶凝胶法制备了不同复合比例的ZnO-TiO₂材料。ZnO-TiO₂复合材料比表面积和孔容孔径尺寸较TiO₂材料均有明显增大,表面酸性更强,能带结构有利于电子空穴的高效分离,催化还原活性与选择性更强。经光催化脱硝实验优化出ZnO与TiO₂最佳复合比为0.2,对于初始质量浓度为6.83 mg/m³的NO_x,在65 W节能灯照射的光源条件下,可见光催化脱除效率高达85%,NO_x质量浓度提高至13.67 mg/m³,在通入氨氮比为1:1的NH₃后,脱硝效率高达96%,比纯TiO₂的提高43%,质量浓度适用范围较前期研究拓宽近六倍。机理分析认为,整个反应可分成吸附与光催化两个部分,其中,吸附是该反应的速控步骤,NO在吸附氧的作用下被氧化为NO     

Cr负载V2O5-WO3/TiO2催化剂的低温NH3-SCR脱硝活性

采用浸渍法制备了一系列不同Cr负载量的CrO_x-V₂O₅-WO₃/TiO₂催化剂, 研究了Cr改性对该催化剂脱硝活性及抗硫性能的影响. 结果表明, Cr的引入使V₂O₅-WO₃/TiO₂催化剂的低温NO_x去除效果和抗硫性能显著提升. Cr的负载量为3%(以Cr₂O₃计算质量分数)时, 催化剂具有最佳的低温脱硝活性和N₂选择性. 结构表征结果表明, 改性催化剂中Cr元素主要以Cr³⁺形式存在, Cr的引入使催化剂的氧化性能明显提升, 并使表面弱酸位点、 强酸位点和催化剂表面吸附氧数量增多. XPS分析结果表明, Cr能使催化剂中V⁵⁺/V⁴⁺比例降低, 促进催化剂中自由电子的迁移. In situ DRIFTs表征结果显示, Cr的引入能促进NO与吸附在Brönsted酸位点上的NH₃在低温条件下反应, 从而使催化剂具有更好的低温脱硝活性. UV-Vis光谱分析结果表明, CrO_x负载量提高会显著增加高价态Cr的烧结聚集. 同时, 提出了一种选择性催化还原(SCR)反应中Cr-V协同催化的机理.     

选择性氧化还原脱硝催化剂

氮氧化物（NO_x）是烟气中的主要污染性气体之一,脱除NO_x已经刻不容缓。本文综述了近年来烟气中NO_x的脱除方法,分析了以钒基催化剂、铁基催化剂、分子筛催化剂为代表的高温脱硝催化剂,讨论了以贵金属催化剂、锰基催化剂、碳基催化剂为代表的低温脱硝催化剂, 阐述了不同温度下选择性催化还原（SCR）脱硝催化剂的反应机理,展望了脱硝领域的发展前景。     

氧化锰基催化剂低温NH3选择性还原NOx反应及其机理*

近年来,氧化锰基催化剂由于在低温氨选择性催化还原（NH₃-SCR）NO_x反应中表现出优良的催化活性得到了广泛的关注。本文综述了氧化锰基催化剂低温NH₃-SCR反应的研究进展,分别分析了氧化锰的氧化态、晶体结构和表面结构以及掺杂离子和载体类型等因素对其催化性能的影响：高的氧化态的锰和高比表面积的催化剂有利于低温NH₃-SCR反应;金属离子如铈、铬、铁、铜和锡等的掺杂可以提高NO_x的转化率和/或N₂选择性;具有独特性能的载体如TiO₂或硅铝分子筛等可以进一步提高氧化锰基催化剂的抗湿和抗硫性能等。本文同时分别对活化NH₃、NO或同时活化NO和NH₃的低温NH₃-SCR反应机理进行了详细总结, 根据不同的反应条件,在氧化锰基催化剂上很多低温NH₃-SCR反应,Eley-Rideal、Langmuir-Hinshelwood以及Mars-van Krevelen 机理可能是同时存在的。本文最后论证和指出了氧化锰基催化剂低温NH3-SCR反应研究的主要发展方向。     

CuO-CeO2-MnOx/γ-Al2O3催化剂选择性催化还原NO

利用溶胶凝胶法制备CuO-CeO₂-MnO_x/γ-Al₂O₃催化剂颗粒,在固定床上测试其催化脱硝活性。CuO-CeO₂-MnO_x/γ-Al₂O₃催化剂在250℃～400℃脱硝效率保持在90%以上。活性组分氧化铈负载量的增多提高了催化剂在低温区脱硝活性。同时利用程序升温方法研究了催化剂对NH₃和NO的氧化性能,随着温度升高NH₃被过度氧化生成了NO和N₂O。催化剂能将NO氧化生成NO₂,但转化程度较低。脱附实验表明,NH₃和NO在催化剂表面存在明显的吸附现象。较少的NH₃吸附量和NH₃过度氧化是高温下脱硝效率降低的主要原因。暂态实验显示,NH₃以吸附态参与反应,而NO以气态或弱吸附态参与反应。     

二氧化碳和丙烯直接合成甲基丙烯酸的NiPMo/TiO2催化剂的研究

用溶胶-凝胶法以磷钼酸(MPA)的镍盐溶液水解钛酸四丁酯制备了NiPMo/TiO2催化剂.使用ICP、 XRD、 TG-DTA、 IR、 TPD-MS和微反应技术研究了催化剂的化学组成、热稳定性、化学吸附性质和催化反应性能.杂多钼酸盐与TiO2通过O2-在TiO2表面发生了键合.在623 K下,杂多阴离子仍保持原有的Keggin结构.CO2在Lewis酸位Ni(Ⅱ)和Lewis碱位Ni-O-Mo的桥氧协同作用下生成CO2卧式吸附态Ni(Ⅱ)←O-(CO)←(O--Ni).丙烯有多种吸附态在催化剂上吸附.在563 K、 1 MPa和空速1500 h-1的反应条件下,丙烯的摩尔转化率为3.2%,产物MAA选择性为95%.     

CoFe2O4自形成磁性液体场致结构化对磁化的影响

The Langevin paramagnetic theory can’t describe the relation between magnetization of ferrofluids and applied magnetic field. The structuralization of ferrofluids, which is considered the main influence factor of the magnetization, is regarded. The part of magnetization works is deposited when the structure is forming. This action influences the magnetization of ferrofluids directly or indirectly. On the base of the “compressing” model, the Langevin function that usually describes the magnetization of ferrofluid is modified, and a well-fitted curve is obtained. An equation of the relation between the equivalent volume fraction after being “compressed” and the intensity of magnetic field is discovered, which approximately describes the process of magnetization. The relation between the approximate initial susceptibility and the volume fraction can be obtained from modified formula.     

Highly regioselective Buchwald–Hartwig amination at C-2 of 2,4-dichloropyridine enabling a novel approach to 2,4-bisanilinopyridine (BAPyd) libraries

The highly regioselective Buchwald–Hartwig amination at C-2 of the cheap and readily accessible reagent, 2,4-dichloropyridine with a range of anilines and heterocyclic amines is described. This new methodology is robust and provides a facile access to 4-chloro-N-phenylpyridin-2-amines on 0.25 mol scale. These intermediates undergo a further Buchwald–Hartwig amination at higher temperature to enable rapid exploration of the chemical space at C-4 and to provide a library of 2,4-bisaminopyridines.     

Sulfur-directed metal-free and regiospecific methyl C(sp3)–H imidation of thioanisoles

Regiospecific and direct imidation of the methyl C(sp³)–H bond of thioanisoles is realized under mild and metal-free conditions with N-fluorobis(benzenesulfonyl)imide as an oxidant and nitrogen source. Proposed mechanism suggests that thionium ion intermediates and a Pummerer-type reaction are involved. The imidation has advantages such as high step-economy, excellent functionality tolerance, and regiospecificity, giving structurally diverse imidation products.     

Selective syntheses of 2H-1,3-oxazines and 1H-pyrrol-3(2H)-ones via temperature-dependent Rh(II)-carbenoid-mediated 2H-azirine-ring expansion

The Rh(II)-catalyzed reaction of 2-carbonyl-substituted 2H-azirines with ethyl 2-cyano-2-diazoacetate or 2-diazo-3,3,3-trifluoropropionate provides an easy access to 2H-1,3-oxazines and 1H-pyrrol-3(2H)-ones. These compounds can be selectively prepared from the same starting material using temperature as the only varied parameter. The 2-azabuta-1,3-diene intermediate, a common precursor for both heterocyclic products, isomerizes into 2H-1,3-oxazine under kinetic control, while 1H-pyrrol-3(2H)-one is the sole product of the reaction at elevated temperatures. According to DFT-calculations a one-atom oxazine ring contraction involving ring-opening to a 2-azabuta-1,3-diene intermediate, followed by a 1,5- and 1,2-prototropic shift leads to the consecutive formation of imidoylketene and azomethine ylide, which then further undergo cyclization to the pyrrole derivative.     

Copper catalyzed/mediated synthetic methodology for ebselen and related isoselenazolones

Scope of the copper catalyzed/mediated selenium-nitrogen coupling reaction has been studied for the synthesis of isoselenazolones. It is noticed that the 2-chloro, 2-bromo-, and 2-iodo-aryl amides substrates can be exploited in the selenium-nitrogen coupling reaction by employing 25-100 mol % of CuI/1,10-phenanthroline (L) and potassium carbonate as a base in DMF. Furthermore, electron rich 2-chloro-arylamides also underwent selenium-nitrogen coupling reaction to give biologically important selenium-nitrogen heterocycles. Also, copper-catalyzed selenium-nitrogen coupling reaction has been meticulously applied for the synthesis of diaryl diselenides having methoxy, amine, and amide functionality from respective aryl iodides in the presence of stoichiometric amount of succinimide as an external Se-N coupling partner.     

Knoevenagel condensation catalyzed by novel Nmm-based ionic liquids in water

A series of novel N-methyl morpholine (Nmm) based ionic liquids with 1,2-propanediol group were synthesized and used as catalysts for Knoevenagel condensation at room temperature in water. Under the effect of the catalyst, various aldehydes or aliphatic ketones could react with a wide range of activated methylene compounds well, including malononitrile, alkyl cyanoacetate, cyanoacetamide, β-diketone, barbituric acid, 2-arylacetonitrile and thiazolidinedione. Furthermore, most of the products could be separated just by filtrating and washing with water. Additionally, the catalyst is recyclable and applicable for the large-scale synthesis.     

Construction of polyheterocyclic spirotetrahydrothiophene derivatives via sulfa-Michael/aldol cascade reaction

A series of polyheterocyclic spirotetrahydrothiophene derivatives were obtained in moderate to excellent yields via a catalyst-free sulfa-Michael/aldol cascade reaction of chalcones 1 and commercially available 1,4-dithiane-2,5-diol 2 under mild conditions. We also present the first asymmetric sulfa-Michael/aldol cascade reaction of chalcones 1 and commercially available 1,4-dithiane-2,5-diol 2 with moderate to good enantioselectivities catalyzed by readily available chiral phase-transfer catalysts (PTCs).     

Suzuki-Miyaura reactions of the soluble guanylate cyclase inhibitor NS2028: a non-product specific route to C-8 substituted analogues

Both soluble guanylate cyclase (sGC) inhibitors ODQ 1 and NS2028 2 are synthesized via improved protocols. In the former case treating 3,4-dihydroquinoxalin-2(1H)-one oxime 8, which can be prepared in two steps from 1,2-benzenediamine, with 1,1′-carbonyldiimidazole (CDI) gives the dihydro-ODQ 10 that in the presence of KMnO₄ oxidises to give ODQ 1 in an overall yield of 46% starting from 1,2-benzenediamine. In the latter case, the synthesis affords NS2028 2 from 2-amino-4-bromophenol 3 in three steps with an overall yield of 85% and avoids the need for chromatography. Furthermore, Suzuki-Miyaura reaction conditions are described that enable the preparation of 8-aryl and 8-heteroaryl derivatives of NS2028 directly from NS2028 2. Finally, demethylation of the 8-(methoxyphenyl) substituted analogues afforded the 8-(hydroxyphenyl) derivatives 40-42. All new products are fully characterised.