太阳能光(电)催化固氮研究进展（英文）

氨(NH₃)是一种现代社会必需的化学物质。目前,工业上合成NH₃仍然采用的是Haber-Bosch过程,即以H₂和N₂为反应物在铁基催化剂的作用下于高温(400-600℃)高压(20-40Mpa)下将N₂转化为NH₃。然而,其效率只有10%-15%,同时造成大量的能源消耗,而且CO₂排放不可避免。开发构建可持续发展的清洁友好的新能源体系是解决能源危机和环境污染问题、实现碳达峰和碳中和的关键战略。半导体光(电)催化固氮可以利用绿色无污染的太阳能制取重要的基础化工原料氨,有望代替传统的化工制氨工艺,解决其能源消耗严重和环境污染的问题。本文概述了光(电)催化固氮反应及其影响因素、光催化、电催化和光电催化固氮反应实验装置与基本特征、光(电)催化固氮反应催化剂研究进展、光电催化固氮反应机理,着重论述了半导体光催化剂、光(电)催化固氮体系以及光催化固氮机理的最新进展,并对太阳能光催化固氮技术加以评述和展望。     

固氮酶的固氮机理和其人工模拟问题的探讨

固氮酶将N₂ 还原为NH₃ 的过程是自然界实现氮循环的重要环节。本文着重对固氮酶的固氮机理和其活性中心FeMo 辅基的人工模拟合成进行探讨, 其中包括FeMo蛋白中的质子和电子的传递, FeMo 辅基对N₂ 的活化方式,Mo 原子的作用, 固氮活性的测试。最后还就固氮酶的活性中心FeMo 辅基的人工模拟合成进行了探讨。     

磷掺杂碳负载ZnxPyOz常温常压下高效电催化合成氨

合成氨(NH₃)的发展是现代工业进程和人类生存的基石。受氮气(N₂)化学惰性的限制,当前的合成氨工业能源消耗高并且排放大量的二氧化碳。电化学氮气还原反应(NRR),是有望取代高能耗的Haber-Bosch (HB)合成法的一种绿色可持续的合成氨工艺。然而,因氮气以及析氢竞争富反应(HER)导致电催化氮气还原极低的NH₃产率和能量转换效率一直是目前人工固氮领域面临的挑战。在本文中,我们报道了一种具有丰富孔结构的磷掺杂碳(PC)负载Zn₃(PO₄)₂/Zn₂P₂O₇纳米复合材料(h-PC/Zn₃(PO₄)₂/Zn₂P₂O₇),在酸性和中性介质中将N₂高效催化转化为NH₃。其独特的分级多孔结构提高了表面粗糙度并加快了氮气在催...     

气体再燃低NOx燃烧中NO与NHi的反应机理研究

采用量子化学密度泛函理论(DFT)对NO与NH_i自由基的反应机理进行了研究,并结合经典过渡态理论对各反应速率常数进行了计算。结果表明,NO与NH₂自由基的反应体系可通过六个反应通道形成N₂+H₂O、N₂O+H₂和N₂H+OH。从能量变化和反应速率两方面考虑,产物N₂+H₂O最容易生成,其最佳反应通道为NO+NH₂→→N₂+H₂O;NO与NH自由基的反应体系可通过七个反应通道形成N₂+OH、N₂O+H和N₂H+O;其中,N₂+OH最容易生成,最佳反应通道为NO+NH→→N₂+OH。比较发现, NH比NH₂自由基更易与NO发生反应生成N₂。因此,在实际运行中改变操作条件,实现NH₂等向NH方向转化,有利于NO_x的还原。     

MnOx/SAPO-11催化剂的制备、表征及其低温NH3-SCR活性

分别采用浸渍法、柠檬酸络合法以及沉淀法在SAPO-11分子筛上负载MnO_x,制备了一系列MnO_x/SAPO-11催化剂。考察了催化剂的低温NH₃选择性催化还原(SCR) (NH₃-SCR) NO_x的性能。结果表明,沉淀法制备的负载量为20%(w)的MnO_x/SAPO-11催化剂表现出最优异的低温NH₃-SCR性能及N₂选择性。通过X射线衍射(XRD)、扫描电镜(SEM)、能量散射谱(EDS)、原子吸收光谱(AAS)、N₂吸附-脱附、X射线光电子能谱(XPS)、H₂程序升温还原(H₂-TPR)、NH₃程序升温脱附(NH₃-TPD)以及NO/O₂程序升温脱附-质谱(NO/O₂-TPD-MS)等多种表征手段对催化剂的结构及表面性质进行分析。表征结果显示,采用不同方法制备催化剂时,其表面MnO_x的存在形式和晶相结构不同。沉淀法制备的催化剂表面存在无定型态MnO_x以及MnO₂晶型,具有较大的介孔及外表面积、更多比例的Mn⁴⁺和化学吸附氧,同时表面存在对反应有利的中强酸以及强酸。因此,催化剂在低温SCR反应阶段能够生成重要中间产物NO₂,从而表现出最佳低温活性。同时,三种制备方法均能使MnO_x相对均匀分散在SAPO-11表面。SAPO-11对催化剂表面MnO_x物种的形成具有一定的影响,从而影响催化剂的酸性,拓宽了MnO_x的活性温度窗口,提高了催化剂的N₂选择性。     

二氧化锰在低温NH3-SCR催化反应上的形貌效应

利用水热法制备了三种不同形貌的MnO₂催化剂,分别为α-MnO₂纳米棒,γ-MnO₂纳米片和δ-MnO₂纳米薄膜组装的微球,考察了纳米材料的形貌结构对催化剂低温选择性催化还原(SCR)反应性能的影响,并利用X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)、N₂吸附-脱附、H₂程序升温还原(H₂-TPR)、NH₃程序升温脱附(NH₃-TPD)、X射线光电子能谱(XPS)以及拉曼(Raman)光谱等表征手段对催化剂的结构进行了分析。结果表明,在50-250 ℃的温度范围内,γ-MnO₂纳米片表现出最优的SCR催化性能,不仅NOx转化率最高而且N₂选择性也最好。表征结果表明,比表面积并不是影响MnO₂催化性能的主导因素,纳米材料的晶型结构与表面暴露的活性晶面共同决定着催化剂的SCR性能。γ-MnO₂纳米片表面暴露的(131)晶面上不仅存在着大量的配位不饱和Mn离子,从而形成了较多的强酸性位点;而且还存在着较多的活性氧物种。这些活性位点可以使得NH₃和NO_x的活化过程在较低温度下进行。高浓度的流动性氧以及高价态的Mn₃₊和Mn⁴⁺也使得催化剂的氧化还原反应更易发生。     

纳秒脉冲介质阻挡放电等离子体合成氨工艺条件优化

氨(NH₃)作为重要的化工原料对农业及国计民生发展有直接影响。工业合成氨需高温高压、能耗高和污染重。低温等离子体技术是一种可持续,有潜力的合成氨途径,已成为国内外研究热点。本工作以氮气和氢气为原料,在低温常压下采用纳秒脉冲介质阻挡放电等离子体合成氨,通过单因素实验系统研究脉冲峰值电压、脉冲重复频率、气体总流量、N₂和H₂体积比(V(N₂)∶V(H₂))等因素对合成氨速率及能量产率的影响规律。进一步通过正交实验评价确定影响合成氨反应速率因素的主次顺序为:脉冲峰值电压>脉冲重复频率>气体体积比>气体总流量。影响合成氨能量产率因素的主次顺序为:脉冲峰值电压>气体体积比>脉冲重复频率>气体总流量。结合两部分实验,最终得到合成氨的优选条件:脉冲峰值电压16 kV、脉冲重复频率6 kHz、脉冲上升沿100 ns、V(N₂)∶V(H₂)=1∶1、气体总流量200 mL/min。此时NH₃合成...     

基于Li-N2电池体系的“连续式”氮气还原合成氨

电化学合成氨近年来受到较多关注, 直接的电化学固氮法(NRR)存在产氨来源不明的问题, 而间接的锂式合成氨(LiNR)被认为是一种可行的固氮方案. LiNR的研究多为电沉积锂, 本工作以Li-N₂电池体系为基础, 利用电池的放电反应固定N₂, 质子源H₂O同时参与反应, 理论上提高了Li-N₂电池的放电电压. 结合充电反应锂盐分解, 构成了清晰的锂循环方案. 研究发现, 当N₂和H₂O共同通入电池, 可以实现连续式的NH₃生产, 且放电电位与理论值接近. 充放电循环显示, 每个循环均可以产生NH₃, 产氨量随循环次数而增加. 该方案可循环利用锂, 对于开发新型的固氮方式有较大的研究与利用价值.     

WO3的引入对MnOx-Fe2O3催化剂上NH3-SCR反应中N2选择性的促进作用

采用溶胶-凝胶法制备了不同含量钨修饰的MnO_x-Fe₂O₃催化剂,重点考察WO₃的引入对NH₃-SCR反应中N₂选择性的影响,通过XRD、BET、XPS、H₂-TPR、Raman和In situ DRIFTS等手段对催化剂的物理化学性质进行表征。结果表明,钨的引入显著提高NH₃-SCR的N₂选择性,当WO₃质量分数为15%时,具有最佳的NH₃-SCR催化性能,且在50-250℃条件下N₂O浓度始终低于0.003%。这主要是由于适量WO₃的引入,导致催化剂物相由α-Fe₂O₃向γ-Fe₂O₃转变,并与锰相互作用形成新的无定型MnWO₄,获得较大的比表面积;使得Mn⁴⁺/（Mn³⁺+Mn⁴⁺）比例减少但Fe²⁺及表面化学吸附氧（O_α）含量增加,从而降低催化剂氧化性;增强催化剂表面的Lewis酸性位点的含量及强度,增强NH₃的吸附,促进了SCR反应,同时抑制了NO₂深度氧化形成硝酸盐物种,降低硝酸盐物种还原产生的副产物N₂O含量,从而显著提高WO₃-MnO_x-Fe₂O₃催化剂在NH₃-SCR中的N₂选择性。     

Cu/Hβ催化剂NH3选择性催化还原NO性能研究

采用浸渍法制备了以Hβ分子筛为载体的负载氧化铜催化剂,考察了Cu负载量对催化剂NH₃选择性催化还原NO反应(NH₃-SCR)性能的影响,通过XRD、N₂吸附-脱附、NH₃-TPD、NO-TPD、H₂-TPR、EDS和XPS等表征技术研究了催化剂的物理化学性质和SO₂存在条件下催化剂活性降低的原因。结果表明,反应气体不含SO₂,Cu负载量为3%,即Cu(3)/Hβ催化剂有较高的反应活性,t₉₅为169℃;反应气体含SO₂,Cu负载量为2%时,即Cu(2)/Hβ催化剂的反应活性较好,t₉₅为225℃。反应前后催化剂的分析结果表明,SO₂存在条件下催化剂活性降低的主要原因是在低温条件下,SO₂与NH₃反应生成的硫铵盐覆盖了催化剂活性中心。     

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.