固体酸催化剂结构与催化反应机理的核磁共振研究

Solid acid catalysts have been widely used in advanced petrochemical processes because of their environmental friendliness, high product selectivity, and easy product separation. Solid-state nuclear magnetic resonance (NMR) spectroscopy is a well-established tool for structure determination and dynamic study of various functional materials. In this review, we focus mainly on our research using solid-state NMR to characterize the acid properties and elucidate the catalytic reaction mechanism of solid acid catalysts. The acid strength of solid acids can be quantitatively measured from the chemical shifts of adsorbed probe molecules such as pyridine, acetone, trialkylphosphine oxides, and trimethylphosphine. The spatial proximity and synergetic effect of various acid sites on solid acid catalysts can be ascertained by two-dimensional (2D) double-quantum magic angle spinning (DQ MAS) NMR spectroscopy. Additionally, in situ solid-state NMR spectroscopy can be used to explore heterogeneous catalytic reaction mechanisms by monitoring the evolution of the reactants, intermediates, and products.     

固体核磁共振技术在固体酸催化剂表征及催化反应机理研究之应用进展

固体酸催化剂广泛应用于现代石油与化学工业中,其反应活性与其酸性密切相关.与传统的酸性表征方法(红外光谱、程序升温脱附、滴定等)相比,利用先进的探针分子技术、双共振和二维相关谱等核磁共振(NMR)技术可以获取固体催化剂酸种类、酸分布、酸浓度和酸强度等完整信息.同时,原位固体NMR实验可跟踪反应分子在催化剂活性中心吸附状态和转换的中间体物种,为揭示反应机理提供了最直接的实验证据.本文详细介绍了固体NMR的原理和一系列相关新技术,着重综述了固体NMR技术在酸催化剂结构、活性中心特性以及催化反应机理方面的应用进展.     

低碳烷烃的多相光催化选择氧化

许多含氧有机物如醇、醛、酮等 ,是化学工业的重要原料 .利用分子氧氧化烷烃生产含氧有机物 ,是化学工业的一个重要过程 .低碳烷烃催化部分氧化的过程往往伴随着初级产物的自氧化 ,从而导致选择性降低 .为了减少反应初级产物的自氧化 ,反应必须维持在烷烃低转化的条件下进行[1] .设计并合成直接将低碳烷烃中的 C- H键有效地选择活化的催化剂 ,是目前催化学科面临的一个艰巨任务 [2 ,3 ] .对于光催化来说 ,一度被寄于厚望的、以金属有机复合物及盐类 [4～ 6]催化低碳烷烃选择氧化为含氧有机物的需氧氧化过程也面临许多困难[7] ,作为研究克服…     

催化裂解低碳烷烃制备碳纳米管薄膜

碳纳米管性质奇特、用途广泛[1]。目前制备碳纳米管薄膜的方法主要有电弧放电法[2]、催化裂解[3]、及真空过滤碳纳米管悬浮液制备“巴基管纸”(Buckypaper)[4]等。本文采用镀镍基板催化裂解低碳烷烃法制备碳纳米管薄膜,考察了镀膜时间、蚀刻和氨水处理等条件对碳纳米管薄膜产物形貌的影响。1　实验部份1 1　镀膜与后处理采用离子溅射法在硅酸盐基板上镀镍,镀镍电流7 5mA,镀镍时间分别为2min、15min、30min、45min或60min;对镀镍基板再进行蚀刻(蚀刻电流7 5mA,蚀刻时间2min)或用氨水浸泡处理(含NH325%,超声振荡30min),然后烘干备用。1 …     

低碳烷烃与二氧化碳催化转化研究进展

页岩气革命为低碳经济发展提供了重要契机.在低碳烷烃(甲烷和乙烷)催化转化过程中,以二氧化碳作为氧化剂参与反应,通过C-H键的选择性活化可将页岩气转化为优质化工原料——合成气和乙烯,是一种低碳烷烃转化与二氧化碳资源化利用的工艺路线.本文总结了近年来甲烷干重整与乙烷和二氧化碳反应中与C-H键活化相关的研究进展,分析了甲烷干...     

ZSM-5分子筛在低碳烷烃脱氢中的催化应用

ZSM-5分子筛是应用广泛的催化体系,常用于烷烃的芳构化、催化裂化及异构化。近年来因其独特的孔道结构及表面酸碱特性,开始应用于低碳烷烃脱氢。本文综述了Zn/ZSM-5及Ga/ZSM-5催化剂对低碳烷烃的脱氢理论研究,概述了Fe/ZSM-5、Cr/ZSM-5、Pt/ZSM-5以及一些其他过渡金属催化剂对低碳烷烃的催化应用;探讨了ZSM-5基催化剂的影响因素如硅铝比、焙烧温度及制备方法等,以利于对低碳烷烃脱氢可作进一步了解;最后对ZSM-5催化体系进行了评述及展望。     

分子水平上低碳烷烃催化选择氧化的初步研究

烃类选择氧化在石油化工中极其重要.近二十多年来,随着石油化工原料逐步从烯烃、芳烃等不饱和烃向资源丰富和价格相对低廉的烷烃的转化,研究烷烃的氧化活化和定向转化来取代相应的烯烃和芳烃工艺具有非常重要的学术意义和工业价值.因而,烷烃的选择活化和氧化得到了世界范围内的     

低碳烷烃选择氧化金属氧化物催化剂的结构与其催化性能的关系

基于金属氧化物催化剂的低碳烷烃选择氧化是催化研究的一个热点和难点, 而认识催化剂的结构与其催化性能之间的关系对于获得高效催化剂, 解决低碳烷烃选择氧化反应中存在的问题至关重要. 本文围绕催化剂的结构对其催化性能的影响, 概述了V-P-O、V-Sb-O、Mo-V-Te-Nb-O和V-Mg-O等几类典型的氧化物催化剂体系在这方面的研究进展. 结合我们开发的Re-Sb-O催化剂体系, 分析了多功能中心、活性位分离、两相协同效应等方面对金属氧化物催化剂的催化性能的影响. 这些认识将有助于设计合成性能优异的催化剂及实现低碳烷烃的选择氧化活化和定向转化.     

层状磷酸铝UT-4的固体核磁共振研究

用吡啶代替四乙二醇作为溶剂, 在Al2O3-H3PO4-C6H11NH2-Py体系下合成出层状阴离子骨架磷酸铝［Al2P3O12H］2-·2［C6H11NH+3］(UT-4)的纯晶相, 采用一维27Al, 31P MAS NMR , 1H→31P CP(Cross Polarization)以及二维27Al- 31P HETCOR(Heteronuclear Correlation)高分辨固体核磁共振技术对其骨架结构进行了表征. 采用两种方法对 27Al信号进行了归属, 并通过分析27Al-31P HETCOR谱对31P 信号进行了归属.     

CO2选择氧化低碳烷烃的研究进展

本文以低碳烷烃的选择催化氧化反应为对象，对几种CO2选择氧化低碳烷烃的反应工艺进行了归纳总结，重点分析讨论了催化氧化反应中CO2作为氧化剂的作用机制，并提出了研究展望。     

SO42−/ZrO2 上异丁烷重构化反应机理的原位核磁共振研究

 采用原位魔角旋转固体核磁共振技术研究了 2-13C-异丁烷在 SO42−/ZrO2 上的重构化反应机理, 考察了反应温度和 H2 气氛对反应的影响. 结果表明, 反应初期, 异丁烷在 SO42−/ZrO2 上的重构化反应以单分子机理为主, 之后向双分子机理转变; 反应温度的升高有利于单分子机理向双分子机理的转变; H2 的存在抑制了异丁烷的重构化反应, 特别对其双分子机理的反应有较强的抑制作用.     

原位固体核磁共振研究温和条件下丙烷在镓改性H-ZSM-5上的活化

将价格低廉、储量丰富的低碳烷烃 ( C1～C5)转化为高附加值的工业产品是多相催化研究中的一个重要领域[1～ 6 ] .镓改性的 H-ZSM-5催化剂已被广泛应用于丙烷芳构化的工业化生产中[7,8] .然而 ,由于低碳烷烃中碳碳和碳氢键的高稳定性 ,低碳烷烃的转化通常需要较高的反应温度 ,因     

表征固体超强酸性的新方法--正丁烷异构化反应的原位13C MAS NMR谱

室温下SO2 -4/ZrO2 催化剂 (SZ)上13 C标记的正丁烷异构化反应的原位13 CMASNMR谱研究结果表明 :其反应动力学符合Langmuir Hinshelwood一级可逆表面反应动力学公式 ,由该动力学公式计算得到的反应速率常数可以用于衡量固体催化剂的表面超强酸性 .这种新的表征方法显示采用一步 -醇热 -超临界干燥综合技术合成的SZ催化剂不仅比表面和硫酸根含量高 ,而且其超强酸性和异构化反应活性均明显优于常规法合成的催化剂 ,具有良好的应用前景 .     

聚酰亚胺／SiO_2杂化材料的硅核磁共振波谱和电光性质的研究

以含氟的二胺5,5’-(六氟异丙基)-二-(2-氨基苯酚)(6FHP)及二酐4, 4’-(六氟异丙基)-苯二酸酐(6FDA)或均苯四甲酸酐(PMDA)为单体,以分散红 1(DR1)为活性生色分子合成具有非线性光学特性的含氟聚酰亚胺,并采用溶胶-凝胶(Sol-Gel)法合成相应的聚酰亚胺／SiO2杂化材料．采用固态29 Si MAS NMR谱研究了含氟聚酰亚胺／SiO2杂化材料的交联结构,结果表明杂化材料中是以T3、Q3、Q4结构为主,说明在杂化材料中形成了交联网状结构．采用衰减全反射(ATR)测定了聚酰亚胺和杂化材料在832 nm处的电光系数,其值分别为 32、28、34和29 pm／V,结果表明具有较高的电光系数．     

Study of Lysozyme Glycation Reaction by Mass Spectrometry and NMR Spectroscopy

The Advanced Glycation End Products (AGEs) are the causative substances of lifestyle‐habit illness. To elucidate the glycation mechanism of the protein, the reaction of lysozyme with D ‐glucose was analyzed by the fluorescence, TOF‐MS, and ¹³C‐NMR spectroscopy under the physiological condition. The fluorescence intensity of lysozyme in the glycation solution increased proportionally with a reaction time of ten weeks. The MALDI‐TOF‐MS spectra of the reaction solution after two weeks showed a peak at m/z 15066, which indicated the presence of a larger molecule than the native lysozyme (m/z 14331), and new peaks at m/z 30105 (dimer) and 45000 (trimer) were also observed. The spectral analysis supported the assumption of a continuous glycation reaction of D ‐glucose with lysozyme and a 30% transformation of lysozyme to the dimeric form during ten weeks. The ¹³C‐NMR spectra of lysozyme showed six [¹³C]‐labeled signals by the glycation reaction with [¹³C]‐glucose after two weeks of reaction. The combined analysis of TOF‐MS and ¹³C‐NMR spectra uncovered that first products of the glycation reaction of lysozyme with D ‐glucose can be observed already three hours after starting the reaction and that nine D ‐glucose units are attached during ten weeks at 37°.     

固体核磁共振高速魔角旋转条件下对称性脉冲零量子同核重耦技术

The considerable demand of robust solid-state nuclear magnetic resonance (NMR) sequences has been met by the development in solid-state NMR hardware and probe design, particularly for fast magic angle spinning (MAS). Fast MAS enhances spectral resolution, however, it makes many conventional methods unusable because of the need of significantly high radiofrequency (RF) field strength and the intrinsic inefficiencies under such condition. Dipolar-based homonuclear recoupling sequences are widely used for structural analysis, and radio-frequency driven recoupling (RFDR) is one of the most popular zero-quantum (ZQ) homonuclear recoupling sequence. Previous studies demonstrated that RFDR efficiency strongly depends on factors such as MAS frequency, resonance offset, RF field inhomogeneity, and chemical shift anisotropy (CSA). To alleviate these dependencies, different RFDR phase cycles have been proposed. To completely understand the principle of ZQ recoupling sequences and achieve uniform broadband homonuclear recoupling under fast MAS conditions, we herein utilize the theory of symmetry sequences and propose a series of RN_N¹ (N ≥ 4, N is even) sequences with various phase cycles under both moderate and fast MAS conditions. We simulated the influence of MAS rate, resonance offset, RF field strength, RF mismatch, and heteronuclear decoupling on ZQ homonuclear polarization transfer efficiency. We verified the ZQ dipolar recoupling efficiencies of various RN symmetry sequences using U-¹³C, ¹⁵N-labeled L-histidine and microcrystalline U-¹³C, ¹⁵N-labeled dynein light chain (LC8) protein. The basic R4 sequence showed the worst broadband ZQ polarization transfer performance theoretically and experimentally, while the basic R6 sequence could efficiently achieve ZQ dipolar recoupling within moderate bandwidth. Under low to moderate MAS conditions, high-power ¹H decoupling could considerably enhance the polarization transfer efficiency, while homonuclear recoupling sans heteronuclear decoupling is recommended under fast MAS conditions. Super phase cycling enhanced ZQ polarization transfer efficiency and bandwidth and resulted in significantly reduced sensitivity to RF mismatch. RN_ixy3 and RN_ixy4 sequences with 6^*N and 8^*N phase cycling steps, respectively, were preferred. The R4_ixy3 sequence with fewer phase cycling steps showed comparable, or even slightly better, performance to the R4_ixy4 sequence. As shown in the simulations, by choosing proper RF field strengths, 1.5^*ω_r < ω₁ < 3^*ω_r, uniform broadband ZQ recoupling with R4_ixy3 or R4_ixy4 sequences could be achieved under fast MAS conditions, which would be significant for the accurate determination of spatial proximities and internuclear distances. By prolonging the mixing time, the RN ZQ scheme could provide more cross peaks, where medium- to long-range spatial correlations could be included; these correlations are essential for structural determination in complex systems.