Generating Parahydrogen-Induced Polarization Using Immobilized Iridium Complexes in the Gas-Phase Hydrogenation of Carbon–Carbon Double and Triple Bonds

Immobilized iridium complexes synthesized using [Ir(COD)Cl]₂ by anchoring on hydrous and anhydrous silica gels were studied in terms of generating parahydrogen-induced polarization (PHIP) in the gas-phase hydrogenation of propylene and propyne. Distinguishing differences in the hydrogenations of carbon–carbon double and triple bonds were found. It has been shown that in the double bond hydrogenation both catalysts are very active even at 25 °C. The reaction yield in continuous flow experiments is more than 70 %, whereas the obtained PHIP degrees are very low. In the case of the triple bond hydrogenation, a more or less active hydrogenation reaction was observed at relatively high temperatures (≈70–80 °C) for the catalyst immobilized on anhydrous silica, while the catalyst immobilized on hydrous silica was inactive at these temperatures. Contrary to the double bond hydrogenation, the triple bond hydrogenation provided significant signal enhancements observed in ¹H nuclear magnetic resonance spectra for the signals corresponding to protons of vinyl fragments of product propylene in both PASADENA and ALTADENA experiments. The catalyst, however, is not stable under the triple bond hydrogenation reaction conditions, and deactivates within several minutes. It was also found that at higher temperatures (100–120 °C), this catalyst demonstrates a reactivation most likely associated with the reduction of Ir(I) that results in the formation of Ir(0) surface metal nanoparticles.     

Parahydrogen-Induced Polarization in Heterogeneous Hydrogenations over Silica-Immobilized Rh Complexes

The use of heterogeneous catalysts for parahydrogen-induced polarization (PHIP) of nuclear spins opens new horizons for production of hyperpolarized substances. Immobilization of homogeneous hydrogenation catalysts is a promising approach for designing the efficient heterogeneous catalytic systems capable of PHIP generation. Herein, we study the formation of PHIP in the gas-phase and in the liquid-phase hydrogenations of propyne and propylene catalyzed by silica-immobilized Rh complexes synthesized by the ligand-exchange anchoring of the Wilkinson’s complex RhCl(PPh₃)₃, the binuclear complex Rh₂Cl₂(C₈H₁₂)₂ and the cationic complex [Rh(C₈H₁₂)₂]⁺[BF₄]^? to the phosphine-modified silica gel. We consider the stability and the mechanistic aspects of the hydrogenation over the immobilized Wilkinson’s catalyst in terms of PHIP observation. Using a PASADENA (parahydrogen and synthesis allow dramatically enhanced nuclear alignment) effect, it is found, in particular, that liquid-phase propyne hydrogenation over the immobilized Wilkinsons’s catalyst at 70°C proceeds in a stable regime with a stereoselective cis addition of a hydrogen molecule, while in the gas phase at the same temperature the hydrogenation stereoselectivity is observed only for a short time after the reaction is started, and then the catalyst rapidly loses its activity. The reasons of the catalyst deactivation are discussed based on the literature data, the results of infrared spectroscopy study, and the comparison to the behavior of the immobilized binuclear and cationic Rh complexes. In addition, it is shown that the immobilized Wilkinson’s catalyst is reduced as temperature increases in the range of 90–130°C, as confirmed by X-ray photoelectron spectroscopy.     

New investigations of technical rhodium and iridium catalysts in homogeneous phase employing para-hydrogen induced polarization

It is shown that the para-hydrogen induced polarization (PHIP) phenomenon in homogenous solution containing the substrate styrene is also observable employing simple inorganic systems of the form MCl₃·xH₂O (M=Rh, Ir) as catalyst. Such observation confirms that already very simple metal complexes enable the creation of PHIP signal enhancement in solution. This opens up new pathways to increase the sensitivity of NMR and MRT by PHIP enhancement using cost-effective catalysts and will be essential for further mechanistic studies of simple transition metal systems.     

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.     

Dipolar induced Para-Hydrogen-Induced Polarization

Analytical expressions for the signal enhancement in solid-state PHIP NMR spectroscopy mediated by homonuclear dipolar interactions and single pulse or spin-echo excitation are developed and simulated numerically. It is shown that an efficient enhancement of the proton NMR signal in solid-state NMR studies of chemisorbed hydrogen on surfaces is possible. Employing typical reaction efficacy, enhancement-factors of ca. 30–40 can be expected both under ALTADENA and under PASADENA conditions. This result has important consequences for the practical application of the method, since it potentially allows the design of an in-situ flow setup, where the para-hydrogen is adsorbed and desorbed from catalyst surfaces inside the NMR magnet.     

1H and 13C solution- and solid-state NMR investigation into wax products from the Fischer-Tropsch process

(1)H and (13)C solid- and solution-state NMR have been used to characterise waxes produced in the Fischer-Tropsch reaction, using Co-based catalysts either unpromoted or promoted with approximately 1 wt% of either cerium or rhenium. The aim was to measure average structural information at the submolecular level of the hydrocarbon waxes produced, along with identification of the minor products, such as oxygenates and olefins, which are typically observed in these waxes. A parameter of key interest is the average number of carbon atoms within the hydrocarbon chain (N(C)). A wax prepared using an unpromoted Co/Al(2)O(3) catalyst had N(C)～20, whilst waxes made using rhenium- or cerium-promoted Co/Al(2)O(3) catalysts were found to have N(C)～21. All three samples contained small amounts of oxygenates and alkenes. The subtle differences found in the waxes, in particular the minor species produced, demonstrate that the different promoters have different effects during the reaction, with the Re-promoted catalyst producing the fewest by-products. It is shown in (13)C solid-state NMR spectra that for that for longer chain (compared to the lengths of chain in previous studies) waxes that the lack of resolution and the complexities added by the differential cross-polarisation (CP) dynamics mean that it is difficult to accurately determine N(C) from this approach. However the N(C) determined by (13)C CP magic angle spinning NMR is broadly consistent with the more accurate solution approaches used and suggest that the wax characteristics do not change in solution. On this basis an alternative approach for determining N(C) is suggested based on (1)H solution state NMR that provides a higher degree of accuracy of the chain length as well as information on the minor constituents.     

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.     

Solid-state NMR concepts for the investigation of supported transition metal catalysts and nanoparticles

In recent years, solid-state NMR spectroscopy has evolved into an important characterization tool for the study of solid catalysts and chemical processes on their surface. This interest is mainly triggered by the need of environmentally benign organic transformations (“green chemistry”), which has resulted in a large number of new catalytically active hybrid materials, which are organized on the meso- and nanoscale. Typical examples of these catalysts are supported homogeneous transition metal catalysts or transition metal nanoparticles (MNPs). Solid-state NMR spectroscopy is able to characterize both the structures of these materials and the chemical processes on the catalytic surface. This article presents recent trends both on the characterization of immobilized homogeneous transition metal catalysts and on the characterization of surface species on transition metal surfaces.     

仲氢诱导极化增强的核磁共振实验条件优化

仲氢诱导极化(Parahydrogen Induced Polarization, PHIP)技术能够极大地增强核磁共振信号,在化学、生物、医学等多方面具有广阔的应用前景．但在实际应用中,通过PHIP技术获得的核磁共振(NMR)信号增强倍数往往受到实际反应条件的影响．该文中以己炔的加氢反应为例,考察了氢气通入方式、反应温度和反应压强对PHIP实验中核磁共振信号增强倍数的影响．     

Effect of ultrasound in enantioselective hydrogenation of 1-phenyl-1,2-propanedione: comparison of catalyst activation, solvents and supports

The enantioselective hydrogenation of 1-phenyl-1,2-propanedione was carried out over Pt/Al2O3, Pt/SiO2, Pt/SF (silica fiber), Pt/C catalysts modified with cinchonidine under ultrasonic irradiation. The initial rate, regioselectivity and enantioselectivity were investigated for different catalyst pretreatments, solvents and ultrasonic powers. The ultrasound effects were very catalyst dependent. The sonication significantly enhanced enantioselectivity and activity of the Pt/SF (silica fiber) catalyst. For the other Pt supported catalysts the reaction rate, enantioselectivity and regioselectivity increased moderately. The choice of solvent influenced the impact of ultrasound effect, namely in mesitylene, which has the lowest vapor pressure, the highest ultrasound enhancement was observed. The effect of sonication on catalysts surface was studied by transmission electron microscopy and scanning electron microscopy (SEM). No significant change in the metal particle size distribution due to sonication was observed. However, in the case of the Pt/SF catalyst, acoustic irradiation induced morphological changes on the catalyst particle surface (SEM), which might be the cause for enhancement of the initial reaction rate and enantioselectivity.     

Immobilizing a single pybox ligand onto a library of solid supports

Chiral pyridinebis(oxazoline) (pybox) ligands can be efficiently immobilized onto silica through position 4 of the pyridine ring. The crucial intermediate in this strategy is 4-chloropybox, which is prepared in good yield from chelidamic acid. 4-Chloropybox reacts with p-hydroxybenzaldehyde and p-aminophenol to give two intermediates (pybox-CHO and pybox-NH2) that allow to introduce the formyl and amino groups able to link to spacers with triethoxysilyl groups. The modified ligands and their ruthenium complexes are immobilized by grafting onto preformed silicas or, alternatively, the support is created by sol-gel synthesis using the functionalized chiral ligand as a silica monomer. In this way it is possible to create a library where the variation involves the support rather than the catalyst. The aim of this approach is to study the influence of different parameters, such as the textural properties of the support and the immobilization method, on the functionalization and catalytic performance. Some of the immobilized complexes are compared as heterogeneous catalysts in the cyclopropanation reaction of styrene with ethyl diazoacetate.     

Diagnosis of deactivation sources for vanadium catalysts used in SO2 oxidation reaction and optimization of vanadium extraction from deactivated catalysts

Physico-chemical analysis (X-ray, FTIR) and/or methanol oxidation reaction test were performed on fresh and deactivated vanadium catalysts used in H₂SO₄ manufacturing. It allowed the diagnosis of catalyst deactivation sources, as well as the processes of regenerating and recycling the worn out catalyst in converter. One of these processes is hydrometallurgical method. It consists in treating the deactivated catalyst with alkaline or acidic reagents and forming vanadate solution. A simple and non-costly operation of chemical attack permits the extraction of vanadium from silica in deactivated catalyst. The extracted vanadium can be used for the confection of regenerated catalysts or metallic tools. After optimization, this method can be used for industrial application.     

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...     

2H-solid-state-NMR study of hydrogen adsorbed on catalytically active ruthenium coated mesoporous silica materials

²H solid-state NMR measurements were performed on three samples of ruthenium nanoparticles synthesized inside two different kinds of mesoporous silica, namely SBA-3 silica materials and SBA-15 functionalized with –COOH groups and loaded with deuterium gas. The line-shape analyses of the spectra reveal the different deuteron species. In all samples a strong –OD signal is found, which shows the catalytic activity of the metal, which activates the D–D bond and deuterates the –SiOH groups through the gas phase, corroborating their usability as catalysts for hydrogenation reactions. At room temperature the mobility of the –Si–OD groups depends on the sample preparation. In addition to the –Si–OD deuterons, the presence of different types of deuterons bound to the metal is revealed. The singly coordinated –Ru–D species exhibit several different quadrupolar couplings, which indicate the presence of several non-equivalent binding sites with differing binding strength. In addition to the dissociated hydrogen species there is also a dihydrogen species –Ru–D₂, which is attributed to defect sites on the surface. It exhibits a fast rotational dynamics at all temperatures. Finally there are also indications of three-fold coordinated surface deuterons and octahedrally coordinated deuterons inside the metal.     

Electrochemical behaviour of oxygen at nickel nest cathodic material with catalyst La1−xSrxCoO3

The reduction of oxygen in the three phases gas–liquid–solid using a nickel nest as electrode with a La_1−xSr_xCoO₃ (x=0, 0.3, 0.5, 0.7, 1) series of combined oxides as a catalyst in different electrolytes of acidic H₃PO₄ or alkaline KOH, NaOH or LiOH solution at a fixed optimum oxygen flow-rate at room temperature was studied by the electrochemical method. The electrochemical parameters, such as electron transfer coefficient and exchange current density, were also determined. The La_1−xSr_xCoO₃ series of catalysts was synthesized by a solid-state reaction. XRD was used to confirm the structure of the catalyst. BET, EDS and resistivity measurements were used to investigated the electrochemical behaviour of the cathodic reduction of oxygen in the presence of the catalyst. SEM was also used to inspect the change before and after the reaction with the catalyst. The electron transfer coefficients, β, from the experiments with the various catalysts in the different alkaline electrolytes were determined as follows:

β(in KOH)>β(in NaOH)>β(in LiOH).

It was discovered that La_0.7Sr_0.3CoO₃ as a catalyst has a higher catalytic activity, a higher specific surface area, lower electrical resistivity, better stability and less agglomeration. Therefore, the above catalyst is the best catalyst for oxygen reduction of those studied.     

Solid-state NMR studies of the adsorption and photooxidation of ethanol on mixed TiO2--SnO2 photocatalysts

In situ solid-state NMR methodologies have been used to investigate the photocatalytic oxidation of ethanol (CH₃CH₂OH) over a series of SnO₂-based photocatalysts. The adsorption of ethanol on commercially available SnO₂ powder was studied using both cross-polarization ¹³C NMR and REDOR experiments, and showed the formation of two surface ethanol species, hydrogen-bonded ethanol at surface hydroxyl groups and ethanol chemisorbed to the SnO₂ surface (Sn–OCH₂CH₃). ¹³C NMR of the adsorbed ethanol was used to characterize the surface of monolayer SnO₂–TiO₂ coupled photocatalysts supported on porous Vycor glass. In situ solid-state NMR studies showed that the photooxidation of ethanol over the monolayer photocatalysts was slower than that over a supported TiO₂ monolayer photocatalyst due to the build-up of reaction intermediates such as acetic acid on the catalyst surface. ¹¹⁹Sn NMR experiments characterized the tin species on the porous Vycor glass support.     

改性VOx/Al2O3催化剂催化氧化甲醇的固体核磁共振研究

采用固体核磁共振研究了NaOH 和HNO₃改性的VO_x/Al₂O₃上甲醇选择性催化氧化反应. 实验结果表明: 在甲醇的氧化反应中, 酸位对二甲氧基甲烷的生成起了重要作用. 与VO_x/Al₂O₃催化剂相比, 酸改性的VO_x/Al₂O₃上的强的Bronsted酸位对二甲氧基甲烷的选择性较高, 没有Bronsted酸位的碱改性的VO_x/Al₂O₃上生成的不是二甲氧基甲烷而是甲酸盐.     

Quadrupolar magic angle spinning NMR spectra fitted using the Pearson IV function

The Pearson IV function was used to fit the asymmetric solid-state ²⁷Al NMR spectra of alumina based catalysts. A high convergence (correlation coefficient is no less than 0.997) between experimental and simulated spectra was achieved. The decomposition of the ²⁷Al NMR spectra of zinc/aluminum mixed oxides with different Zn/Al molar ratio revealed an increased fraction (6–9%) of pentacoordinated aluminum atoms in these oxides as compared to γ-Al₂O₃. As the Zn/Al ratio is raised, the fraction of [AlO₆] octahedral units decreases, while the fraction of [AlO₄] tetrahedra increases.     

Solid-state nuclear magnetic resonance investigations of the nature, property, and activity of acid sites on solid catalysts

Further progress in the field of heterogeneous catalysis depends on our knowledge of the nature and behavior of surface sites on solid catalysts and of the mechanisms of chemical reactions catalyzed by these materials. In the past decades, solid-state NMR spectroscopy has been developed to an important tool for routine characterization of solid catalysts. The present work gives a review on experimental approaches and applications of solid-state NMR spectroscopy for investigating Brønsted and Lewis sites on solid acids. Studies focusing on the generation of surface sites via post-synthesis modification routes of microporous and mesoporous materials support the development of new and the improvement of existing catalyst systems. High-temperature and flow techniques of in situ solid-state NMR spectroscopy allow a deeper insight into the mechanisms of heterogeneously catalyzed reactions and open the way for studying the activity of acidic surface sites. They help to clarify the activation of reactants on Brønsted and Lewis acid sites and improve our understanding of mechanisms affecting the selectivity of acid-catalyzed reactions.     

天然焦-H2O气化反应特性

在加压热重分析仪上研究了气化温度和催化剂种类对沛城煤矿天然焦-H2O的气化反应特性的影响,用扫描电镜(SEM)观察不同温度下焦样的孔隙结构,并计算了动力学参数.结果表明,气化温度是影响天然焦-H2O气化反应性的一个主要因素,随着温度的升高,天然焦的孔隙越发达,碳转化率明显增大;K基、Ni基、Fe基三种催化剂均能有效地促进气化反应,其中K基催化剂效果最好,其次是Ni基和Fe基催化剂;天然焦的活化能为Eα=147.25 kJ/mol.