富氧条件下Ag/Al2O3-Cu/Al2O3组合催化剂催化乙醇选择性还原NOx

 在富氧条件下,以乙醇为还原剂,考察了不同金属负载量的Ag/Al2O3和Cu/Al2O3催化剂选择性还原NOx的活性. 结果表明,4%Ag/Al2O3和10%Cu/Al2O3分别为各自体系中的最佳催化剂. 4%Ag/Al2O3具有很高的选择性催化还原NOx的活性,但同时会产生一定量的副产物CO. 10%Cu/Al2O3选择性催化还原NOx的活性不高,但却具有很好的消除CO的活性. 将4%Ag/Al2O3和10%Cu/Al2O3以不同方式组合,其评价结果表明,4%Ag/Al2O3-10%Cu/Al2O3组合催化剂具有与单纯4%Ag/Al2O3相似的NOx脱除活性,同时能够完全消除反应过程中产生的CO,并且能大大降低尾气中乙醇和乙醛的浓度.     

富氧条件下Ag/Al2O3和Cu/Al2O3组合催化剂催化C3H6选择性还原Nox的性能

 在全自动催化剂活性评价装置上,考察了富氧条件下Ag/Al2O3和Cu/Al2O3两种催化剂上催化丙烯还原NOx的活性. 在实验温度范围(200～650 ℃)内,Ag/Al2O3具有 优异的催化丙烯选择性还原NOx的活性,但同时有大量副产物CO形成. Cu/Al2O3选择性催化丙烯还原NOx的活性不高,却能有效促进CO的氧化. 在无水条件,Ag/Al2O3-Cu/Al2O3组合体系具有与Ag/Al2O3相似的脱除NOx活性,同时使CO在300 ℃以后几乎完全转化. 在10%水蒸气存在的情况下,Ag/Al2O3-Cu/Al2O3组合催化剂脱除NOx的活性下降,但水蒸气对CO转化率的影响不大.     

新型铬锰复合氧化物低温选择性催化氨还原NOx

采用柠檬酸法合成了一系列铬锰复合氧化物催化剂,利用X射线衍射及X射线光电子能谱研究了催化剂活性相态,并考察了铬锰摩尔比对反应活性的影响. 结果表明,该体系在有氧条件下氨低温选择性催化还原氮氧化物反应中显示出优异的活性,其中Cr(0.4)-MnOx催化剂具有最佳低温催化活性,在空速 30 000 h-1和120 ℃条件下, NOx转化率达98.5%, N2选择性达100%. 在MnOx中添加Cr后形成了CrMn1.5O4晶相, 该相态在低温选择性催化还原NOx过程中起重要作用.     

Al-PILC负载铜铁复合氧化物在NH_3选择性催化还原NO中的协同作用

以铝柱撑黏土(Al-PILC)为载体采用旋蒸-浸渍法制备了铜、铁单组分催化剂(Cu/Al-PILC、Fe/Al-PILC)和铜铁复合氧化物催化剂(CuFe/Al-PILC),并测试其对NH3选择性催化还原NO反应(NH3-SCR)的催化性能。相比Cu/Al-PILC和Fe/Al-PILC,CuFe/Al-PILC活性组分之间有较强的协同效应,显著提高了催化剂的脱硝性能。CuFe/Al-PILC在290~450℃的宽温区NO脱除效率保持90%以上,最高可达97%。此外,CuFe/Al-PILC有很好的抗水抗硫性能,催化活性不受反应气氛中水蒸气和SO2的影响。XRD、UV-vis、XPS和N2吸附脱附表征结果表明,CuFe/Al-PILC中活性组分相互作用生成CuFe2O4,有利于活性组分在载体表面分散,提高催化剂的比表面积和孔容;H2-TPR表征结果表明,CuFe/Al-PILC活性组分在载体表面生成的CuFe2O4改善了催化剂氧化还原性能,有利于NH3对NO选择性的还原;NH3-TPD表征结果表明,CuFe/Al-PILC在较宽温区范围内对NH3都有很好的吸附,这有利于提高催化剂表面还原物种的浓度,从而保证催化剂在较宽温区范围内具有较好的NO脱除效率。     

负载型锰氧化物催化剂催化NH3选择性还原NOx

使用浸渍法制备了Mn/TiO2,Mn/Al2O3,Mn/ZrO2,Mn-Y(Y=Ce,Fe,Ni,Co)/TiO2催化剂,用XRD,BET对催化剂进行了表征,同时在模拟NH3选择性还原NOx的反应条件下对催化剂的活性和选择性进行了考察.结果表明,载体的性质明显影响了Mn氧化物催化剂的活性,其中Mn/TiO2催化剂具有更佳的催化NH3选择性还原NOx的催化活性;Ce,Fe等其他金属的添加显著提高了Mn/TiO2催化剂的催化活性;随着Mn-Ce负载量的增加,Mn-Ce/TiO2催化剂的活性有显著提高.     

Pt/Al2O3催化剂用于丙烯选择性还原NO

分别采用浸渍法(IM)和溶胶-凝胶法(SG)制备了一系列不同铂负载量的催化剂, 在固定床反应器上用C3H6作还原剂, 测试了选择性还原NOx的活性, 结果发现, 在IM法和SG法制备的催化剂中, 活性组分铂最佳负载质量分数分别为0.5%和2%. 针对两种催化剂, 分别考察了氧浓度、丙烯浓度及反应气流量对选择性催化还原NOx性能的影响, 催化活性随丙烯浓度的增大而上升. 2%Pt/Al2O3(SG)催化剂的抗SO2性能好于0.5%Pt/Al2O3(IM)催化剂, H2O的存在可明显拓宽活性温度范围, 并向高温区间移动, 在200～400 ℃范围内可有效净化NOx.     

银在甲烷选择性催化还原NOx反应中不同催化行为的研究

 采用XRD,TEM和UV－Vis方法研究了Ag－HZSM－5催化剂中活性组分银的价态和结构变化,并将这种变化与其在CH4选择性催化还原NOx反应中的活性和选择性相关联．结果表明,惰性气氛下高温处理使交换到分子筛阳离子位上的Ag＋自还原为Ag0,并在热的作用下聚集成纳米尺度的银颗粒Agn．纳米银颗粒Agn的形成提高了银催化剂在CH4选择性催化还原NOx反应中的活性,但它的长大又促进了CH4和O2的直接燃烧,使CH4选择性催化还原NOx反应的选择性降低．氧气气氛下高温预处理抑制了银颗粒的长大,并且氧气的氧化作用使银颗粒带有一定电荷,形成小的荷电纳米银粒子Agy＋x．荷电纳米银粒子的形成使催化剂的活性降低,但提高了CH4选择性催化还原NOx反应的选择性．     

Pd基催化剂上H2快速选择催化还原 NOx

 首次研究了 Pd 基催化剂上氢快速选择催化还原 NOx 反应 (快速 H2-SCR 反应). 结果表明, Pd/Al2O3 和 Pd/SiO2 催化剂表现出极高的活性, 在 200 oC 以上时 NOx 转化率可达 100%; 但 Pd/MgO 催化剂在整个考察温度范围均没有活性, 这表明载体对催化剂快速 H2-SCR 活性有决定性作用. 与常规 H2-SCR 反应相比, 快速 H2-SCR 反应明显提高了 NOx 的消除效率. 原位漫反射红外光谱结果表明, 快速 H2-SCR 反应活性的提高来源于加速生成的氨物种以及后续反应速率的加快.     

贫燃条件 In-Ag/TiO2-γ-Al2O3催化 CO选择性还原NO

汽车尾气中主要污染成分 CO和 NOx可导致酸雨、光化学烟雾和臭氧空洞效应,对生物、环境及生态系统造成重大危害。污染源中 CO是性能优良的还原剂,如能不添加还原剂实现 CO催化还原 NOx,将成为最具经济技术优势的 NOx脱除技术。在富氧、低温条件下,利用 CO选择性催化还原 NOx为 N2,是目前选择性催化还原研究中的热点和难点。催化 CO还原 NOx常用的贵金属 Ir, Rh, Pt和Pd矿藏稀少,价格昂贵,有氧条件下活性急降,而分子筛催化剂和一些金属氧化物催化剂普遍存在反应温度高,尤其对 N2选择性差等问题。为解决上述问题,需寻找新的适合我国矿产资源的催化体系。研究发现,稀散金属基催化剂对氮氧化物的净化具有一定效果,因而可将我国的稀散金属资源优势转化为技术优势和经济优势。因此,本文以 TiO2-γ-Al2O3(TA)为载体, In/Ag为活性组分,采用等体积浸渍法制备了 InAg/TA以及 In/TA, Ag/TA和InAg/Al (γ-Al2O3为载体)催化剂,考察了贫燃条件下 CO选择性还原NO的催化活性。研究表明,双金属催化剂InAg/Al和 InAg/TA的活性比单金属催化剂In/TA和 Ag/TA高, In/TA催化剂中引入 Ag物种能降低起燃温度;另外,相比于InAg/Al催化剂, InAg/TA催化剂具有较高的催化活性,550?600°C时 N2产率超过60%,说明载体中引入TiO2可以提高催化剂活性。为了深入研究 InAg/TA催化剂中 Ag物种和TiO2对 In物种的作用,通过比表面测定、X射线衍射(XRD)、透射电子显微镜(TEM)、X射线光电子能谱、紫外-可见光吸收光谱、氢气程序升温还原、傅立叶变换红外线光谱等方法分析了催化剂结构和表面形态。结果表明, Ag物种可以提高 In物种的分散性, In和 Ag物种在 TA载体表面可以很好地分散,从而有利于提高催化活性。 In和 Ag物种在 TA载体表面以氧化态形式存在,并且 Ag物种可以提高 In物种表面含量,表面 In和 Ag物种含量越高,吸附活性位越多,催化活性越高;同时, TiO2也可以促进 NO吸附,从而提高 InAg/TA催化剂活性。 InAg/TA催化剂在450°C连续反应72 h进行稳定性测试,测试前后分别在50?600°C进行活性测试,并用 XRD和 TEM对反应后的催化剂进行表征测试。结果表明, InAg/TA催化剂具有较好的稳定性,连续反应前后催化剂活性基本保持不变,推测可能由于在有 CO和O2存在的体系中, Ag物种利用自身 Ag+与 Ag0之间的氧化还原反应抑制了活性组分 In2O3的还原和聚集,稳定了 In物种乃至催化剂活性。 InAg/TA催化剂用于贫燃条件下CO还原NO具有较好的催化效果,主要归因于催化剂活性组分分散性好,稳定性高,对NO吸附能力强。 Ag物种可以稳定In物种并提高其分散性, TiO2可以改善In物种和Ag物种的分散性并促进NO吸附。     

新型贵金属修饰的Ag/Al2O3催化剂选择性催化还原NOx的催化性能及反应机理

 在富氧条件下研究了几种贵金属修饰的Ag/Al2O3催化剂选择性催化还原(SCR)NOx的活性和反应机理. 催化活性实验结果表明,在模拟柴油机尾气的实验条件下,5%Ag-0.01%Pd/Al2O3在300~500 ℃范围内显示出很高的NOx转化率,而Pt和Au的添加均使Ag/Al2O3的NOx转化率明显降低. 原位漫反射傅里叶变换红外光谱结果显示,添加少量的Pd在反应过程中有利于丙烯部分氧化形成烯醇式(C=CH-O-)活性中间物种,该物种对NO2和NO-3的反应活性很高,能够生成关键中间体异氰酸酯(-NCO),从而加速NOx催化还原反应.     

α-Amino acid derived enaminones and their application in the synthesis of N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates and other heterocycles

A new and simple synthesis of novel N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates, which exist in equilibrium with their 4-oxo tautomers, has been developed in two steps starting from N-protected α-amino acids. The key intermediates are enaminones, which can also be isolated, characterized, and used for the construction of other functionalized heterocycles, before they spontaneously decompose to pyrrole products. 4-Hydroxypyrroles are prone to partial aerial oxidation but can be efficiently alkylated or reduced to stable polysubstituted pyrrolidine derivatives.     

Specific intramolecular aromatic CH insertion of diazosulfonamides

The chemoselectivity in the intramolecular CH insertion of various diazosulfonamides has been experimentally studied. The results reveal that the aliphatic 1,4-, 1,5-, or 1,6-C(sp³)?H insertions of diazosulfonamides are not accessible, while the aromatic 1,5-C(sp²)?H insertion can be realized specifically by adjusting the diazo-adjacent group. In addition, the general chemoselectivities in the intramolecular CH insertions of diazosulfonyl compounds are summarized. Generally, diazosulfones undergo both aromatic 1,5-C(sp²)?H and aliphatic 1,5- and 1,6-C(sp³)?H insertions, while diazosulfonates undergo aliphatic 1,5- and 1,6-C(sp³)?H insertions. However, diazosulfonamides only undergo aromatic 1,5-C(sp²)?H insertion.     

N-Heterocyclic carbene-palladacyclic complexes: synthesis,characterization and their applications in the C-N coupling and α-arylation of ketones using aryl chlorides

N-Heterocyclic carbene-palladacyclic complexes 3 were successfully achieved in a one-pot procedure under mild conditions. The structure of 3a was unambiguously confirmed by X-ray single crystal diffraction and it was an active catalyst in the Buchwald-Hartwig amination and α-arylation of ketones even at very low catalyst loadings (0.01?mol%).     

Iodine-mediated oxidative Pictet-Spengler reaction using terminal alkyne as the 2-oxoaldehyde surrogate for the synthesis of 1-aroyl-β-carbolines and fused-nitrogen heterocycles

An efficient iodine-mediated oxidative Pictet-Spengler reaction in dimethyl sulphoxide (DMSO) using terminal alkynes as the 2-oxoaldehyde surrogate for the synthesis of aryl (9H-pyrido[3,4-b]indol-1-yl)methanones is described. The scope of the protocol includes the total synthesis of Fascaplysin, Eudistomins Y₁ and Y₂. The methodology is extended for preparing pyrrolo[1,2-a]-quinoxaline and indolo[1,5-a]quinoxaline derivatives. The utility of 1-aroyl-β-carbolines was demonstrated by performing palladium-catalyzed β-carboline directed ortho-C(sp2)-H functionalization of the phenyl ring with thiomethyl (SMe) group using DMSO as source and for accessing 4-aryl-canthin-6-ones.     

Facile synthesis of bicyclic 1-arylpyrazol-5-ones

In this Letter, we described a facile method for constructing fused bicyclic 1-arylpyrazol-5-one ring system. We employed various methylene-containing carboxylic acids as the substrates and proved that the pyrazolone ring closure requires activated methylene group in intermediate II. Accordingly, a series of structurally diversified, fused bicyclic 1-arylpyrazol-5-ones was prepared in moderate to high yields using the requisite substrates.     

A carbanion induced synthesis of highly congested pyrazole and imidazole containing heterocycles

An efficient approach to the synthesis of highly congested di, penta and hexacyclic pyrazoles as well as imidazole fragment containing novel heterocyclic molecule has been developed through a carbanion induced transformation of suitably functionalized 2H-pyran-2-ones, benzo[h]chromene and thiochromeno[4,3-b]pyrans. Due to the presence of fluorescence, we report their prime application metal sensor as off/on switching in ferric ions.     

Synthesis of pyrrolo[1,2-a]pyrazines and pyrazino[1,2-a]indoles by Curtius reaction in Morita-Baylis-Hillman derivatives

Synthesis of substituted pyrrolo[1,2-a]pyrazines and pyrazino[1,2-a]indoles from the Morita-Baylis-Hillman derivatives of acrylates via saponification followed by Curtius reaction is described.     

Selective synthesis of 4,5-dihydroimidazo- and imidazo[1,5-a]quinoxalines via modified Pictet–Spengler reaction

An efficient tandem approach for the selective synthesis of 4,5-dihydroimidazo[1,5-a]quinoxalines 6a–g and imidazo[1,5-a]quinoxalines 7a–h by the reaction of 2-imidazolyl anilines 4a–c with aryl aldehydes 5a–k under mild reaction conditions is described. Introduction of electron releasing alkyl groups in substrates 4a–b was found to be instrumental for the success of the reaction.     

Understanding the Diels-Alder reactivity of 1,2-azaborine analogues

The Diels-Alder reactivity of 1,2-heteroborines (H₄C₄B(H)X, X?=?NH, PH, AsH; O, S, Se) has been computationally explored by means of Density Functional Theory (DFT) calculations. The influence of the HB?=?X fragment on the reactivity of the system has been quantitatively analyzed in detail by means of the so-called Activation Strain Model (ASM) of reactivity. It is found that the interaction between these species and the dienophile is significantly stronger than that computed for their all-carbon isoelectronic counterpart, benzene. In addition, the strain energy plays a key role in the observed reactivity trends. The role of the aromaticity strength of these heteroarenes on the reactivity is also assessed.