光催化甲醇重整机理的原位核磁共振研究

本文利用原位核磁共振技术在真实固液反应环境中对光催化甲醇重整过程进行了研究.研究发现，体系中甲醇重整的液态中间产物主要有四种：HOCH₂OH、CH₃OCH₂OH、HCOOH和HCOOCH₃.不同晶型的二氧化钛催化剂会影响这四种产物的生成趋势.随光照时间的增加，上述四种产物的含量均会增加.Pd负载对一级中间产物CH₃OCH₂OH和HOCH₂OH的产率影响较大，其产率为无Pd负载的2~3个数量级；对二级中间产物HCOOCH₃和HCOOH的产率影响较小.     

原位核磁共振技术研究反应环境对光催化甲醇重整过程的影响

本文利用原位核磁共振技术,系统研究了在真实反应体系中反应环境（气氛、压强、气体量等）对甲醇光催化重整反应产物的影响.发现不同气氛对甲醇光催化重整的反应产物有着不同的抑制作用,而环境压强及气体量对于甲醇光催化重整反应产物产率的影响较小.在此基础上,本文进一步讨论了气体在催化剂表面的吸附方式和环境气氛影响甲醇光催化重整反应产物的机理.     

Pd-Cu双金属催化剂上加氢反应的仲氢诱导超极化研究

本文通过多相催化-仲氢诱导超极化（HET-PHIP）核磁共振（NMR）技术研究了Pd-Cu/SiO₂双金属催化剂上丙炔选择性加氢反应.首先利用等体积浸渍法和连续浸渍法合成了一系列不同Pd/Cu比例和形貌的Pd-Cu/SiO₂双金属催化剂.通过ALTADENA（Adiabatic Longitudinal Transport After Dissociation Engenders Net Alignment）方法发现,催化剂的Pd/Cu比例和形貌均对PHIP的极化效率有较大影响.随着Pd-Cu双金属催化剂中Pd比例的增大,PHIP极化效率降低,同时反应活性增强.在同Pd/Cu比例下,相对于等体积浸渍法,连续浸渍法制备的层叠形貌催化剂具有较弱的极化效率以及较强的催化活性,这是由于催化剂表面暴露出的Pd数量增多,导致催化活性增强;同时单个Pd集簇表面积增大,使得氢原子移动范围扩大,从而造成极化效率降低.     

原位核磁共振技术研究共催化剂类型以及光照波长对甲醇光催化重整产物的影响

本文采用原位核磁共振的方法研究了在真实固-液环境中共催化剂类型以及光照波长对甲醇光催化重整产物及光解水产氢产率的影响.结果发现,不同贵金属担载的锐钛矿型二氧化钛催化剂对甲醇光催化重整产物的产量和产率有着不同程度的影响,但是对其动力学特征影响不大.光照波长对甲醇光催化重整产物的产量也影响较大.通过对比甲醇氧化产率与产氢产率,发现共催化剂的种类对光催化反应速率及氧化还原能力起重要作用,且共催化剂的种类会影响体系氧化和还原能力之间的协同性.     

Pd-Sn双金属催化剂催化1,3-丁二烯加氢反应的仲氢诱导极化研究

本文首先利用等体积共浸渍法合成了一系列Pd/Sn比(原子比)不同的Pd₁-Sn_x/Al₂O₃双金属催化剂,然后通过多相催化仲氢诱导极化(PHIP)技术研究了Pd-Sn/Al₂O₃双金属催化剂上1,3-丁二烯选择性加氢反应．结果发现催化剂的Pd/Sn比会影响1,3-丁二烯反应活性和丁烯选择性：随着Pd/Sn比的下降,反应中1,3-丁二烯转化率降低,丁烯选择性提高．利用PASADENA(parahydrogen and synthesis allow for dramatically enhanced nuclear alignment)技术,发现Pd/Sn比的变化影响了1-丁烯与2-丁烯之间的异构化过程：随着Pd/Sn比的下降,1-丁烯异构化率降低,这是由于Sn组分含量的提高减少了表面暴露的Pd组分,使得催化剂反应活性降低;Sn组分含量的提高同时导致了Pd电子密度的上升,使得选择性还原产物丁烯更易脱附,阻止其进一步加氢生成丁烷,并抑制了1-丁烯异构化反应过程...     

固体核磁共振技术在甲醇制烯烃反应中的应用

甲醇制烯烃过程是由非石油路线生成低碳烯烃的重要途径之一.分子筛因具备独特的孔结构和可调变的酸性质,而成为甲醇制烯烃过程的核心催化剂.固体核磁共振(NMR)是鉴定物质结构、阐释催化反应机理的强有力的工具,在甲醇制烯烃的研究中被广泛应用.本文主要总结了近年来利用原位固体NMR、多维多核NMR、脉冲梯度场NMR等固体NMR技术研究甲醇制烯烃反应机理取得的重要进展.原位固体NMR可以在真实反应条件下监测催化反应中反应物、中间体和产物的动态演变过程;多维多核NMR可以在不破坏催化剂结构情况下确定反应中间体结构信息,特别是¹²⁹Xe NMR可以很灵敏探测反应中催化剂的孔道结构变化;脉冲梯度场NMR可用于测定孔道内分子的扩散系数,阐明分子筛的扩散机制.     

复合管道气液固三相流浆体水击压强和水击波速计算

浆体中的含气量对水击压强和波速产生重要的影响。提出了考虑含气量的浆体即气液固三相流浆体水击波速计算公式,分析了考虑气泡的存在对浆体水击波速的影响,对某一复合管道内气液固三相流浆体水击压强进行了计算.     

高分辨魔角旋转核磁共振技术（HR/MAS）在固相合成中的应用

使用微量探头分析了不同树脂、溶剂、温度对¹H NMR线宽的影响，并运用高分辨魔角旋转核磁共振技术跟踪固相载体上羟基氨基酸的糖基化反应. 该研究表明使用高分辨魔角旋转核磁共振探头可以快速、直接鉴定树脂上的产物，是固相合成中重要的分析工具.     

Rh基催化剂上氢甲酰化反应过程的原位高压NMR研究

制备了用于丙烯氢甲酰化反应的Rh/SBA-15 和PPh₃修饰的PPh₃-Rh/SBA-15催化剂. 应用原位变温高压核磁共振技术,对比研究了丙烯在Rh/SBA-15 和PPh₃修饰的多相催化剂PPh₃ Rh/SBA-15上的氢甲酰化反应,实现了高压条件下催化反应的原位固体核磁共振表征. ¹³C MAS NMR研究结果表明：在1.0 MPa的反应压力下,随着反应温度升高丙烯与合成气在Rh/SBA-15催化剂上可转化生成丁醛,而PPh₃配体修饰的PPh₃-Rh/SBA-15催化剂上丁醛产物的正异比显著提高.     

CO吸附和加氢反应过程的原位高压MAS NMR研究

应用原位变温高压MAS核磁共振技术,对比研究了CO在不同Rh基催化剂上的吸附和加氢反应过程. ²⁹Si MAS NMR研究结果表明：Rh基催化剂中加入金属助剂后,载体Silicate-1上的表面硅羟基减少,助剂金属与硅羟基作用锚锭在载体表面.¹³C MAS NMR研究结果表明：当引入CO/H2混合气后,在Rh/Silicate-1催化剂上只能观测到气相CO、线式吸附CO和孪式吸附CO的快速交换信号;而在Rh-Mn/Silicate-1和Rh-Mn-Li/Silicate-1催化剂上,还观测到了倾斜式吸附的CO共振信号,表明助剂Mn或Mn-Li的加入促进了CO的吸附. 随着反应温度升高,CO/H₂在Rh/Silicate-1催化剂上转化生成CO_²,进一步升高温度会有CH₄生成;而CO/H₂在RhMnLi/Silicate-1催化剂上反应活性更高,在较低的温度下就会转化生成CO₂,但未观测到甲烷的生成. ¹H MAS NMR 谱显示,反应后载体Silicate-1上硅羟基的量会减少,表明CO与载体部分表面硅羟基反应生成了CO₂.     

Understanding the leaching properties of heterogenized catalysts: a combined solid-state and PHIP NMR study

Para-hydrogen induced polarization (PHIP) NMR in solution, combined with solid-state NMR, can be efficiently employed for the highly sensitive in-situ detection of the leaching properties of immobilized catalysts. The knowledge of this property is important for possible applications of PHIP experiments in medicine, biology or industry, where leached catalysts poison the solution of hyperpolarized products. As experimental example Wilkinson's catalyst RhCl(PPh(3))(3) (1) immobilized on mesoporous silica is chosen. As model reaction the hydrogenation of styrene in solvents with different polarities (methanol-d(4), acetone-d(6) and benzene-d(6)) is used. A (31)P solid-state MAS-NMR study reveals that there are two different species of catalysts on the silica, namely coordinatively bound catalysts and physisorbed catalyst. Only the second species exhibits substantial leaching, which is visible in a strong PHIP enhancement of the reaction product.     

原位低场核磁共振弛豫法定量监测光催化Cr(Ⅵ)还原反应

本文利用原位低场核磁共振（LF-NMR）技术在真实固液反应环境中对光催化还原Cr（Ⅵ）反应进行了定量研究,并对Ag纳米颗粒负载量不同的Ag担载石墨相氮化碳复合光催化剂（Ag/g-C₃N₄）在可见光照射下催化Cr（Ⅵ）还原为Cr（Ⅲ）的性能进行了研究.研究发现,Ag纳米颗粒负载（负载量分别为1 wt.%、2 wt.%、5 wt.%和10 wt.%）可以有效提高g-C₃N₄的光催化性能;且负载量为5 wt.%时光催化性能最优,为无Ag负载的g-C₃N₄的4倍.此外,本文还通过横向弛豫时间（T₂）定量分析了反应体系中顺磁性Cr（Ⅲ）离子的浓度,证实了采用LF-NMR弛豫法评价光催化Cr（Ⅵ）还原反应性能的可行性.     

Metal–Organic Framework Supported Palladium Nanoparticles: Applications and Mechanisms

Heterogeneous palladium (Pd)‐based catalysts are extensively applied to improve the catalytic performance and/or expand the reaction scope in many catalytic processes, involving the cross‐coupling, hydrogenation, reduction, and oxidation reactions. Among them, metal–organic framework (MOF)‐supported Pd nanoparticles (Pd NPs) are becoming the most popular one for their excellent catalytic performance and reusable property. To motivate the development of this technology, the applications of MOF‐supported Pd NPs (Pd NPs/MOFs) in heterogeneous catalysis are critically summarized herein, including the hydrogenation reduction of nitro‐ and polyunsaturated compounds, synthesis of carbon–carbon (C? C) bonds compounds, chromium (Cr(VI)) reduction, dehalogenation, alcohol oxidation, CO₂ conversion, and CO oxidation. The influences of base, solvents, electron character of substitutes, and type of halogen on the catalytic performance are comprehensively discussed. Finally, the application prospects of Pd NPs/MOFs and existing shortcomings in the catalytic field are proposed.     

Pd/C催化剂在乙炔选择加氢反应中的催化性能：载体效应

Pd/C catalysts were prepared by deposited Pd nanoparticles (NPs) on different carbon supports including activated carbon (AC), graphite oxide (GO), and reduced graphite oxide (rGO) using sol-immobilization method. Through transmission electron microscopy, powder X-ray di raction, and X-ray photoelectron spectroscopy, the role of the carbon supports for the catalytic performances of Pd/C catalysts was examined in selective hydrogenation of acetylene. The results indicate that Pd/AC exhibited higher activity and selectivity than Pd/GO and Pd/rGO in the gas phase selective hydrogenation of acetylene. Thermal and chemical treatment of AC supports also have some effect on the catalytic performance of Pd/AC catalysts. The differences in the activity and selectivity of various Pd/C catalysts were partly attributed to the metal-support interaction.     

Ultrasonically improved semi-hydrogenation of alkynes to (Z-)alkenes over novel lead-free Pd/Boehmite catalysts

This paper reports the application of ultrasound in the semi-hydrogenation of alkynes over two novel Pd/Boehmite catalysts. The semi-hydrogenations of phenylacetylene, diphenylacetylene and 2-butyne-1,4-diol have either been investigated in an ultrasonic bath under atmospheric hydrogen pressure, or in an ultrasonic horn reactor under 0.1–0.5 MPa hydrogen pressure. Alkyne hydrogenation was suppressed by sonication under atmospheric hydrogen pressure, but promoted by sonication under 0.1 MPa of hydrogen pressure. Sonication increased selectivity towards the semi-hydrogenated products in both cases. Catalyst loading, hydrogen pressure, temperature and the presence of quinoline, all impacted on hydrogenation rate, activity and selectivity to semi-hydrogenated products. Palladium leaching from the catalyst was evaluated in ethanol and hexane both under plain stirring and sonication.