NMR研究超稳Y分子筛水热老化过程中结构与酸性的变化

利用固体核磁共振（NMR）结合探针分子技术,探讨了超稳Y分子筛在水热老化过程中酸中心结构和酸性的变化规律.结果表明,水热老化初期,大量的骨架铝脱出最终形成了非骨架五配位铝,使得丙酮探测到的Brønsted酸（B酸）酸量随着老化时间的增加而减少.而非骨架五配位铝会向表面迁移并形成多聚铝,使得分子筛中Lewis酸（L酸）酸量也随老化时间的增加而减少.在老化过程的前3 h内,酸量的变化幅度较大.整体硅/铝原子比相等的分子筛,其B酸酸量的变化幅度与新鲜剂的晶胞大小呈正比;随着老化时间的继续增加,不同配位的铝物种的含量趋于稳定,B酸和L酸的酸量变化幅度很小.在整个水热老化过程中,超稳Y分子筛中B酸和L酸的协同效应一直存在,由协同效应产生的一种酸性增强的B酸位的稳定性最好.     

SSZ-13分子筛上甲醇转化过程中甲氧基物种的生成与活性研究

本文使用固体核磁共振（NMR）技术研究了SSZ-13分子筛上甲醇制烯烃反应过程中表面甲氧基物种的生成以及反应活性.通过二维¹³C-²⁷Al HMQC NMR方法确证了甲醇在分子筛骨架Brønsted酸位上生成的甲氧基物种,以及在Lewis酸位上生成的另外一种表面甲氧基物种.¹³C NMR结合气相色谱-质谱（GC-MS）实验结果表明,这两种甲氧基物种在甲醇制烯烃反应中均具有较高的反应活性,既可以导致烃池物种的生成,也可以参与烃池反应生成碳氢化合物.     

Probing the evolution of water clusters during hydration of the solid acid catalyst H-ZSM-5

A technique developed recently for in situ solid-state ¹H NMR studies of adsorption processes has been used to probe hydration of the solid acid catalyst H-ZSM-5, yielding information on the interaction between the adsorbed water molecules and Brønsted acid sites on the H-ZSM-5 host material. Quantitative analysis of the results from the in situ experiment allows the average size of water clusters associated with the Brønsted acid sites to be determined directly, and suggests that there is a preference to form clusters comprising five–six water molecules. The in situ ¹H NMR data also provide insights into kinetic aspects of the adsorption process.     

Crystallization of metallic nanoparticles on short DNA oligonucleotides in alkaline aqueous solution

Journal of Nanoparticle Research - A series of nickel phosphide catalysts with adjustable Brønsted acid sites and Lewis acid sites has been prepared by liquid-phase method using...     

六氟硅酸铵后处理对H-ZSM-5分子筛酸性影响的固体NMR研究

本文利用固体核磁共振（NMR）实验对六氟硅酸铵（AHFS）溶液洗涤前后H-ZSM-5分子筛上铝物种变化引起的酸性改变进行了研究.结果显示经AHFS洗涤处理后，分子筛上构成Brøsted酸的骨架四配位铝物种会部分减少；具有Lewis酸性的骨架三配位铝量在经AHFS脱铝处理后少量降低；同时AHFS温和脱铝的方式主要会引起分子筛上另一类具有Lewis酸性且含Al-OH的铝物种大量减少，从而导致处理后分子筛整体酸性的显著改变.     

Investigation on the Beckmann rearrangement reaction catalyzed by porous solids: MAS NMR and theoretical calculations

In the last years, ‘in situ’ solid-state NMR has been applied to investigate the Beckmann rearrangement of oximes into amides using zeolites and mesoporous materials of different structure containing Brønsted acids or silanol groups as active sites. DFT methods have been applied to model the geometry of the complexes resulting from adsorption of reactants, reaction intermediates and products on clusters representing the zeolite centers, and their ¹⁵N and ¹³C NMR chemical shift calculated theoretically. This article reviews the results reported in the bibliography on the Beckmann rearrangement of various oximes (acetophenone oxime, cyclohexanone oxime and cyclododecanone oxime) mainly using ‘in situ’ ¹⁵N NMR spectroscopy and theoretical calculations, and are compared with those obtained by ‘in situ’ infrared spectroscopy. The combination of experiment and theory has been shown to be very useful for the interpretation of the NMR spectra and the identification of the species present at different reaction temperatures.     

五配位铝强化硅铝固体酸的固体核磁共振研究

Brønsted酸（B酸）是无定型硅铝（ASAs）表面最重要的催化活性位点.通常认为B酸位的形成只依赖于不饱和四配位铝（Al^IV）,且仅具有弱B酸性.通过合成五配位铝（Al^V）富集的ASAs能够大幅提升高铝硅比（Al/Si）时的B酸含量及强度,克服传统Al^IV富集的ASAs的酸性强化瓶颈.本文介绍了Al^V在ASAs酸性强化及合成单原子催化剂中的重要作用.通过采用多种二维固体核磁共振（SSNMR）及原位质子NMR技术,证明了Al^V能够大量富集在ASAs表面,着重介绍了两种基于Al^V的新B酸位的形成机制,并阐明了Al^V诱导单原子催化剂在ASAs表面形成的机理.     

Changes in the functional chemical composition of the surfaces and microhardness of kimberlite minerals under the action of nanosecond high voltage pulses

Using a set of physicochemical methods (XPS, analytical electron microscopy, the adsorption of acid–base indicators, and measuring microhardness), the effectiveness of nonthermal action produced by nanosecond high voltage pulses for targeted changes in the phase (functional chemical) composition and technological properties of rock-forming minerals of kimberlites and diamonds is shown. According to data obtained via XPS and SEM-EDX analyses, pulse energy actions damage the surface microstructure of dielectric minerals with the subsequent formation of traces of surface breakdowns and microcracks, softening rockforming minerals, and reducing their microhardness by 40–66% overall. The following changes in the functional chemical composition of a geomaterial surface are established through the adsorption of acid–base indicators: mutual transformations of the Brønsted base, Lewis base, and Brønsted acid sites on a calcite surface under the action of an electromagnetic pulse and the hydroxylation and/or formation of carbonyl groups on a diamond surface, doubling the diamond electrokinetic potential in the negative range.     

Mass spectrometric study of the mechanism of the ionization of nitrogen-containing organic compounds on the surface of a molybdenum microalloyed alloy

Experimental studies of the mechanism of surface ionization of amines on the surface of a microalloyed molybdenum alloy in the air at atmospheric pressure were performed. The products of surface ionization of triethanolamine, Dimedrol, and papaverine were studied using a high-resolution mass spectrometer. The physicochemical parameters of surface ionization of some organic nitrogen compounds were measured. It was shown experimentally that the ionization of organic compounds of this type on the surface of the heated molybdenum alloy in air at atmospheric pressure occurs by a mechanism involving Brønsted sites (Brønsted).     

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.     

Comparative studies of Zr-based MCM-41 and MCM-48 mesoporous molecular sieves: Synthesis and physicochemical properties

Two surfactant-templated synthetic routes are developed for the preparation of new types of mesoporous molecular sieves, Zr-MCM-41 and Zr-MCM-48, using different Si sources but keeping the same zirconium precursor (zirconium-n-propoxide). When fumed silica was used as Si precursor, a Zr-MCM-48 material of cubic structure was formed with a surface area of 654.8 m²/g and an unimodal pore diameter distribution. It shows low stability: after calcination at 600 °C, the ordered structure was transformed into a relatively disordered worm-like mesostructure with many defects and silanol groups. The use of tetraethyl orthosilicate as Si source led to the formation of a Zr-MCM-41 mesoporous solid, which had good thermal stability and a highly ordered hexagonal arrangement, with a surface area 677.9 m²/g and an uniform pore diameter distribution. Fourier transform infrared (FT-IR) characterization and ²⁹Si NMR analysis confirm that zirconium ions indeed incorporated into the framework of the solid. The in situ FT-IR spectroscopy of pyridine adsorption reveals that both, Lewis and Brönsted acid sites, were formed on the surface of these mesoporous materials. The strength and number of the Brönsted acid sites of the Zr-MCM-48 solid were greater than those of the Zr-MCM-41, due to a lower degree of condensation reaction during the synthesis that led to more structural defects in the framework and more silanol groups stretching from the solid surface.     

固体核磁共振研究固体酸催化剂酸性进展

酸性直接与固体酸催化剂的活性相关,因此研究固体酸催化剂的酸性受到了科研工作者的广泛关注. 固体核磁共振技术已经成为研究固体酸催化剂酸性的一种强有力的工具. 该文介绍了固体核磁共振的特点和各种常用技术,着重综述了固体核磁共振研究固体酸催化剂酸性的进展.     

Effect of substitution of oxygen by sulfur in the nonleaving group of a carbonate: kinetics of the phenolysis and benzenethiolysis of S‐methyl aryl thiocarbonates

The phenolysis and benzenethiolysis of S‐methyl 4‐nitrophenyl thiocarbonate ( 1 ) and S‐methyl 2,4‐dinitrophenyl thiocarbonate ( 2 ) in water are studied kinetically. The Brønsted plots (log k _N versus nucleophile basicity) are linear for all reactions. The Brønsted slopes for 1 and 2 are, 0.51 and 0.66 (phenolysis) and 0.55 and 0.70 (benzenethiolysis), respectively. These values suggest a concerted mechanism for these reactions, as found in the corresponding carbonates. Namely, substitution of OMe by SMe in the nonleaving group does not change the mechanism. Copyright © 2007 John Wiley & Sons, Ltd.     

Proton transfer rate‐equilibria in apolar aprotic solvents: a historical perspective

Low dielectric constant apolar aprotic solvents, although employed on a limited scale for studying proton transfer reactions as compared with commonly used polar protic or dipolar aprotic ones, offer some particular advantages, namely, specific solute–solvent interactions are virtually eliminated and proton transfer occurs directly in an apolar aprotic solvent. An intriguing feature of these reactions is their general acid‐catalyzed/base‐catalyzed kinetics with a time scale over microseconds to minutes. In fact, the true or intrinsic relative strengths of acids/bases when measured in such solvents come to the fore much more clearly than those obtained in other classes of solvents. Recently, a review documenting the post‐1980 developments relating to proton transfer reactions in apolar aprotic solvents has been published. The present article is a commentary of the pre‐1980 developments in this area since the 1920s Brønsted–Lowry's “proton cult” of acid–base theory. Copyright © 2016 John Wiley & Sons, Ltd.     

Conduction and diffusion in exchanged montmorillonite clays

The temperature dependences for conductivities and ¹H NMR relaxation times are reported for homionic (exchanged) montmorillonite clays. Ionic conductivity in the interlayer region is primarily protonic (H⁺), arising from the Brønsted acidity of hydrated interlayer cations. Hydrogens outside the hydration shell appear to undergo translation by chemical exchange.     

Complexability of o-bisguanidinobenzenes with arsenic and phosphoric acids in solution and solid states, and the potential use of their immobilized derivatives as solid base ligands for metal salts and arsenic acid

The role of o-bisguanidinobenzenes (BGBs) as new Brønsted base ligands for arsenic and phosphoric acids was examined. In solution state, complexation was evaluated by Job’s plot in ¹H NMR experiment, indicating a 1:1 complex formation, whereas in solid state crystalline structures of complexes obtained were addressed by X-ray crystallographic analysis and/or solid state ¹³C NMR experiment, in which 1:2 complexes between the BGB and the acid components were normally formed. Based on these results, Merrifield and Hypogel^® resin-anchored BGBs were designed and prepared as the corresponding polymer-supported host ligands. Evaluation of their coordination ability with metal salts (ZnCl₂ and CoCl₂) and arsenic acid in aqueous media by ICP-MS showed that the latter Hypogel^® resin-anchored BGBs acted as effective immobilized base ligands.     

Chiral poly-rare earth metal complexes in asymmetric catalysis

Asymmetric catalysis is a powerful component of modern synthetic organic chemistry. To further broaden the scope and utility of asymmetric catalysis, new basic concepts for the design of asymmetric catalysts are crucial. Because most chemical reactions involve bond-formation between two substrates or moieties, high enantioselectivity and catalyst activity should be realized if an asymmetric catalyst can activate two reacting substrates simultaneously at defined positions. Thus, we proposed the concept of bifunctional asymmetric catalysis, which led us to the design of new asymmetric catalysts containing two functionalities (e.g. a Lewis acid and a Brønsted base or a Lewis acid and a Lewis base). These catalysts demonstrated broad reaction applicability with excellent substrate generality. Using our catalytic asymmetric reactions as keys steps, efficient total syntheses of pharmaceuticals and their biologically active lead natural products were achieved.     

Further experimental evidences of thermal spreading of tungsten oxide on zirconia

The effects brought about by the time of thermal treatment as well as the water content in the gas phase during the thermal spreading of WO₃ on zirconia were investigated. Diffuse reflectance UV-vis spectroscopy evidenced the thermal spreading phenomenon and revealed the formation of polymeric tungsten dispersed species. Neither the thermal treatment time nor the water content showed to influence the nature of the dispersed species, which reveal to present thermodynamically preferential molecular structures. Infrared spectroscopy analysis of adsorbed pyridine evidenced that the polytungstate species lead to the generation of Brönsted acid sites. Lewis acid sites stronger than those naturally present on zirconia could also be detected in addition to weaker Lewis sites, which were associated to the WO₃ still present in the catalysts as showed by X-ray diffraction.     

Assessment of surface acidity in mesoporous materials containing aluminum and titanium

The surface acidity of mesoporous molecular sieves of aluminum and titanium was evaluated using four different techniques: n-butylamine volumetry, cyclohexylamine thermodesorption, temperature-programmed desorption of ammonia and adsorption of pyridine. The nature, strength and concentration of the acid sites were determined and correlated to the results of a probe reaction of anthracene oxidation to 9,10-anthraquinone (in liquid phase). In general, the surface acidity was highly influenced by the nature, location and coordination of the metal species (Al and Ti) in the mesoporous samples. Moderate to strong Brönsted acid sites were identified for the Al-MCM-41 sample in a large temperature range. For mesoporous materials containing Ti, the acidity was represented by a combination of weak to moderate Brönsted and Lewis acid sites. The Ti-HMS sample exhibits a higher acidity of moderate strength together with a well-balanced concentration of Brönsted and Lewis acid sites, which enhanced both conversion and selectivity in the oxidation reaction of anthracene.