NO 和 NO2 在 V2O5/AC 催化剂表面的反应行为

 采用程序升温脱附、在线质谱和原位漫反射红外光谱等手段, 比较了 NO 和 NO2 在 V2O5 及 V2O5/AC 催化剂表面的选择催化还原 (SCR) 反应行为. 结果表明, 氨以质子态 NH4+和共价态 NH3 分子两种形态吸附于纯 V2O5 表面, V=O 为氨的主要吸附活性位. 无氧状态下, NO 和 NO2 皆可与吸附于 V2O5 表面的 NH3 反应, 并且 NO2 与吸附态 NH3 的反应活性高于 NO. 但在 V2O5/AC 催化剂表面, 同样在无氧条件下, NO 几乎不与吸附态 NH3 反应, 而 NO2 却可以反应并生成 N2. 在 V2O5/AC 表面, NO 很容易被气相 O2 氧化为 NO2, 然后参与 SCR 反应. 可见, NO2 是 NO 在 V2O5/AC 表面发生 SCR 反应的中间体.     

V2O5/ACF催化剂低温下选择性催化还原NO的机理

将V2O5担载在活性炭纤维(ACF)上制得V2O5/ACF催化剂,并采用暂态响应实验和NH3吸附氧化实验等考察了影响V2O5/ACF催化剂上选择性催化还原(SCR)反应的关键因素.结果表明,NH3在催化剂表面的吸附是必要的,而且该吸附是一个快速过程;气相O2的存在有利于形成催化剂中所需的活性氧化态物种.NH3吸附.脱附与原位质谱相结合的实验表明,V2O5/ACF催化剂具有吸附NH3和将NH3氧化为N2H2的能力,N2H2为NH3氧化的一种中间体.     

氨再生条件对V2O5/AC同时脱硫脱硝活性的影响

对烟气同时脱硫脱硝过程中吸附SO2后的活性炭载V2O5（V2O5/AC）催化 吸附剂在含NH3气氛下的再生条件进行了考察,发现3%～5%NH3/Ar气氛、300℃、60min再生可有效恢复V2O5/AC的脱硫活性,并明显提高其脱硝活性。基于对SO2和NO的脱除率、再生后V2O5/AC的硫质量分数以及FT IR谱图分析发现,NH3的存在对V2O5/AC所吸附硫的脱附行为没有明显影响,但可显著改变V2O5/AC的表面化学性质,有利于烟气脱硫;NH3还可在V2O5/AC表面储存,显著促进脱硝。     

同时脱除烟气中硫和硝的V2O5/AC催化剂研究

通过在固定床微反应器上对同时脱硫脱硝催化剂的研究,发现将V2O5担载在活性焦(AC)上制得的V2O5/AC催化剂可在200 ℃同时脱除烟气中的SO2和NO,其活性明显高于纯AC。V2O5/AC催化剂的脱硫脱硝活性与催化剂中钒的质量分数有关,随着V2O5质量分数从0.5%增至9%,硫容从3%增加到12%,脱硝率在V2O5质量分数为0.5%到3%时脱硝率稳定在60%左右,继续增加V2O5质量分数,脱硝率降低。程序升温脱附 (TPD) 和红外光谱 (FTIR) 表征结果显示在脱硫脱硝过程中,催化剂表面有H2SO4, 铵盐和VOSO4生成, VOSO4的质量分数随催化剂中V2O5质量分数的提高而升高。使用后的催化剂可通过5%NH3在300 ℃再生,再生后催化剂的脱硝活性明显增加,NO转化率从新鲜样的67%提高到接近100%,对SO2的吸附也比新鲜样有所增加。     

介质阻挡放电等离子体与吸附在CuZSM-5上的NO或NO/O2的相互作用

采用吸附和程序升温脱附(TPD)技术研究了介质阻挡放电等离子体对CuZSM-5催化剂上吸附的氮氧化物作用. 实验表明, 介质阻挡放电等离子体使催化剂表面吸附的NO及Cu活性位上吸附的NOx物种脱附, 并引发表面化学反应生成新的氮氧化物. 对于NO/N2体系, 介质阻挡放电等离子体与吸附在CuZSM-5上NO作用, 主要生成N2O和O2. 在富氧体系NO/O2/N2, 则生成较大量的N2O、NO2和NO. 等离子体预处理活性下降的CuZSM-5, 可明显提高其催化分解NO活性. 对比有或无介质阻挡放电等离子体预处理NO或NO/O2饱和吸附的CuZSM-5上的NO-TPD结果表明, 等离子体提高催化剂活性的原因与其使催化剂Cu活性位上吸附的NOx物种脱附有关.     

介质阻挡放电等离子体与吸附在CuZSM-5上的NO或NO/O2的相互作用

采用吸附和程序升温脱附(TPD)技术研究了介质阻挡放电等离子体对CuZSM-5催化剂上吸附的氮氧化物作用.实验表明,介质阻挡放电等离子体使催化剂表面吸附的NO及Cu活性位上吸附的NOx物种脱附,并引发表面化学反应生成新的氮氧化物.对于NO/N2体系,介质阻挡放电等离子体与吸附在CuZSM-5上NO作用,主要生成N2O和O2.在富氧体系NO/O2/N2,则生成较大量的N2O、NO2和NO.等离子体预处理活性下降的CuZSM-5,可明显提高其催化分解NO活性.对比有或无介质阻挡放电等离子体预处理NO或NO/O2饱和吸附的CuZSM-5上的NO-TPD结果表明,等离子体提高催化剂活性的原因与其使催化剂Cu活性位上吸附的NOx物种脱附有关.     

燃煤烟气中碱金属化合物对V2O5/AC催化剂低温脱硝的影响： NH3的吸附与氧化

采用湿法浸渍-再干燥法将K₂O和K₂SO₄担载到低温SCR催化剂V1/AC上,模拟研究了烟气中超细碱金属颗粒物对V1/AC催化剂脱硝活性的影响。结果表明,两种含K化合物的引入均导致了该催化剂的失活,明显抑制了NH₃在催化剂上的吸附,尤其是热稳定性较低的吸附;K₂SO₄的抑制作用明显小于K₂O,这与它们对催化剂SCR活性的影响规律相一致。K₂O的担载对催化剂表面的氧化性能影响较小,但由于其能抑制NH3的吸附而引起催化剂的失活;K₂SO₄的担载则增加了催化剂表面吸附态的NH₃在O₂气氛中被过度氧化为NO的可能性。     

富氧条件下Co/ZSM-5催化剂对C_3H_8选择还原NO_x的性能

采用多种物理化学手段研究了在模拟的轻型柴油车尾气中不同Co担载量及Cu掺杂的Co/ZSM-5催化剂的Co组分分散状态、可还原性、NO吸附脱附性质对C3H8选择性催化还原NOx性能的影响。结果表明,浸渍法制备的Co/ZSM-5催化剂上既有外表面上的Co3+和Co2+物种,也有孔内的Co2+离子。富氧条件下Co/ZSM-5催化剂上C3H8选择性催化还原NOx的活性主要与ZSM-5载体孔外表面分散的CoOx物种中的钴离子可还原能力和NO吸附脱附性能密切相关。Co/ZSM-5催化剂上适宜的Co担载量约为4.0wt%,低担载量时随Co担载量增加,表面CoOx物种中钴离子可还原能力增强,C3H8选择性催化还原NOx的低温转化活性增加;高担载量时,随Co担载量增加,单位Co离子的NO吸附量的减少以及催化剂表面活性中心数的减少,导致了Co/ZSM-5催化剂NOx的转化率和催化剂比速率(k)的下降。孔外表面Co3O4晶体的存在使催化剂表面产生较强的NO吸附,并在高温时有利于C3H8的氧化燃烧,使C3H8选择性催化还原NOx的活性降低。     

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φNH3/φNO=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。     

不同活性焦载体对V2O5/AC催化剂脱硫活性的影响

活性焦载体的选择是制备高活性烟气脱硫催化剂的关键.以四种煤制活性焦(AC)为载体,制得了系列V2O5/AC催化剂.通过脱硫活性评价、催化氧化能力测试和孔结构分析表明,AC表面的高活性氧化位较少,担载V2O5使AC表面产生了新的高活性氧化位,其脱硫活性显著提高;V2O5在具有高比表面积和较大孔容的载体上分散性较好,能够形...     

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%.     

Synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives

Different approaches for the synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives from simple amino acids have been investigated. A library of 33 precursors for the preparation of N-hydroxy pyrazinones was obtained in moderate to good yields.     

Toward new camptothecins. Part 6: Synthesis of crucial ketones and their use in Friedländer reaction

In the context of the preparation of camptothecin and luotonin A analogs, the synthesis of some key keto-precursors and their use in Friedländer condensation are described. This paper also focuses on the stability of these keto intermediates and emphasizes the major differences between indolizinones and pyrroloquinazolinones series. Noteworthy is also the report of some original structures isolated as by-products of some experiments.     

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.     

KMnO4-mediated oxidative CN bond cleavage of tertiary amines: Synthesis of amides and sulfonamides

KMnO₄-mediated oxidative CN bond cleavage of tertiary amines producing secondary amine was introduced, which was trapped by electrophiles (acyl chloride and sulfonyl chloride) to form amides and sulfonamides. The reaction could take place at mild condition, tolerating a wide range of function groups and affording products in moderate to excellent yields.     

Chemistry of heterocyclic compounds at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, over 50 years (Review)

The review contains a concise historical account and information on the most significant researches undertaken by the staff at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences on the Chemistry of Heterocyclic Compounds. Dedicated to Academician of the Russian Academy of Sciences B. A. Trofimov on his 70th jubilee. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1443–1502, October, 2008.     

A general and convenient synthesis of 4-(tosylmethyl)semicarbazones and their use in amidoalkylation of hydrogen,heteroatom, and carbon nucleophiles

A general synthesis of previously unknown semicarbazone-based α-amidoalkylating reagents, 4-(tosylmethyl)semicarbazones, has been developed. The synthesis involved three-component condensation of semicarbazones of aliphatic or aromatic aldehydes with the same or other aldehydes and p-toluenesulfinic acid. The scope and limitations of this reaction were investigated. The compounds obtained were demonstrated to be an efficient α-(4-semicarbazono)alkylating agents. They were reacted with H- (sodium borohydride), O- (sodium methylate), S- (sodium phenylthiolate), N- (pyrrolidine, sodium succinimide), P- (trialkyl phosphites), and C-nucleophiles (sodium diethyl malonate) to give the corresponding products of the tosyl group substitution, 4-substituted semicarbazones, including analogues of nitrofurazone. Among the prepared compounds tested in vitro for antibacterial and antifungal activity, three nitrofuryl-containing semicarbazones exhibited high biological activities with minimum inhibitory concentration (MIC) values of 8–32 μg/mL.     

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.     

Synthesis of novel chiral bidentate hydroxyalkyl-N-heterocyclic carbene ligands and their application in palladium-catalyzed Mizoroki–Heck couplings and asymmetric addition of diethylzinc to benzaldehyde

A small library of new chiral bidentate hydroxyalkyl-imidazolium salts 1 is conveniently synthesized on multi-gram scale from inexpensive and commercially available chiral pool amino acids. The corresponding carbenes, generated by deprotonation of imidazolium salts 1, in combination with palladium(II) chloride were tested in the Mizoroki–Heck coupling reaction. The most significant results in terms of yields and reactivities were achieved with low catalyst loading. The catalytic activities of these imidazolium salts were also investigated in the asymmetric addition of diethylzinc to benzaldehyde. The use of MgO nanoparticles as an additive in conjunction with these ligands played a crucial role in increasing the efficiency of these reactions.