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111.
112.
113.
A new infrared-spectroscopic method to characterize acid sites of zeolites using small and weakly basic molecules such as diatomic and monoatomic molecules is reviewed. It has been revealed that N2 is an effective probe molecule to characterize both Brønsted acidity and Lewis acidity of H-form zeolites. The characteristics of the N 2 probe are discussed in detail in comparison with the CO probe. O2 and rare gases have also been applied to monitor the strong acid sites in the H-form zeolites. Further, the studies of the adsorption of water on H-form zeolites are shortly reviewed: a recent IR study of the H2
18O adsorption on H-ZSM-5 has given direct experimental evidence that the main feature of the observed IR bands is due to the hydrogen-bonded adsorption of water on the Brønsted acid sites. 相似文献
114.
《Journal of separation science》2017,40(4):954-961
In this work, we developed a capillary column modified with zeolitic imidazolate framework‐8 as a novel stationary phase for open‐tubular capillary electrochromatography. To immobilize zeolitic imidazolate framework‐8 onto the inner surface of silica capillary, a bio‐inspired polydopamine functionalization was used to functionalize the capillary surface with polydopamine. First, a polydopamine layer was assembled inside the capillary. Second, due to noncovalent adsorption and covalent reaction ability, polydopamine could attract and anchor zeolitic imidazolate framework‐8 onto the inner surface of capillary. It has been demonstrated that zeolitic imidazolate framework‐8 was successfully grafted on the inner wall of the capillary by scanning electron microscopy, and Fourier transform infrared spectroscopy. The electro‐osmotic flow characteristics of capillaries were also investigated by varying the pH value and acetonitrile content of mobile phase. The zeolitic imidazolate framework‐8 coating not only increased the phase ratio of open‐tubular column, but also improved the interactions between tested analytes and the stationary phase. Three groups of isomers including acidic, basic, and neutral compounds were well separated on the zeolitic imidazolate framework‐8 bonded column, with theoretic plate numbers up to 1.9 × 105 N for catechol. The repeatability of the prepared columns was also studied, and the relative standard deviations for intra‐ and interday runs were less than 5%. 相似文献
115.
采用并流共沉淀法制备了不同Zr/Cd原子比(nZr/nCd)的ZrCdOx金属氧化物,并与水热法制备的不同硅铝比(nSiO_(2)/nAl_(2O3))的片状SAPO-18分子筛物理混合制得ZrCdOx/SAPO-18双功能催化剂,研究了其催化CO2加氢直接合成低碳烯烃性能。采用透射电子显微镜(TEM)、X射线衍射(XRD)、N2吸附-脱附、CO2程序升温脱附(CO2-TPD)、NH3程序升温脱附(NH3-TPD)和X射线光电子能谱(XPS)对催化剂进行了分析。与单一ZrO2相比,引入CdO使得ZrCdOx比表面积下降,当nZr/nCd=8时制备的Zr8Cd1氧化物呈现出无定形小颗粒状,Zr与Cd之间较强的协同作用使得Zr Cd Ox氧化物产生了更多的氧空位,有利于CO2的吸附活化。通过对Zr8Cd1金属氧化物与SAPO-18(硅铝比0.1)的质量比、工艺反应温度、压力和空速对催化性能影响的考察,获得了最佳反应条件。研究还发现,当SAPO-18的硅铝比从0.1降为0.01时,Br?nsted酸含量降低,产物中烯烃/烷烃物质的量之比从18.6提高至37.2,但副产物CO含量迅速增加,低碳烯烃时空收率明显下降。 相似文献
116.
Jerzy Podobiski Mariusz Gackowski Grzegorz Mordarski Katarzyna Samson Micha
liwa Dorota Rutkowska-Zbik Jerzy Datka 《Molecules (Basel, Switzerland)》2021,26(15)
The properties of both Cu2+ and Cu+ ions in zeolite CuY were followed with NO and CO as probe molecules. Cu2+ was found to be located in SII, SII*, and SIII sites, whereas Cu+ was found in SII and SII* sites. The fine analysis of the spectra of Cu2+-NO and Cu+-CO adducts suggests that both in SII and in SII* sites two kinds of Cu cations exist. They differ in the positive charge, which may be related to the varying numbers of AlO4− in close proximity. The experiments of NO and CO adsorption and desorption evidenced that both Cu2+ and Cu+ sites of highest positive charge bind probe molecules most strongly but activate them to a lesser extent than the Cu sites of lowest positive charge. The experiments of reduction with hydrogen evidenced that the Cu ions of higher positive charge are first reduced by hydrogen. On the other hand, Cu sites of the lowest positive charge are first oxidized by oxygen. The experiments with CuNaY zeolites of various Cu contents suggest that the first introduced Cu (at low Cu contents) created Cu+, which was the most neutralized by framework oxygens. Such Cu cations are the most stabilized by framework oxygens. 相似文献
117.
Dr. James P. Dombrowski Dr. Micah S. Ziegler Dr. Neelay M. Phadke Erum Mansoor Dr. Daniel S. Levine Dr. Ryan J. Witzke Prof. Dr. Martin Head-Gordon Prof. Dr. Alexis T. Bell Prof. Dr. T. Don Tilley 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(1):307-315
Anionic molecular models for nonhydrolyzed and partially hydrolyzed aluminum and gallium framework sites on silica, M[OSi(OtBu)3]4− and HOM[OSi(OtBu)3]3− (where M=Al or Ga), were synthesized from anionic chlorides Li{M[OSi(OtBu)3]3Cl} in salt metathesis reactions. Sequestration of lithium cations with [12]crown-4 afforded charge-separated ion pairs composed of monomeric anions M[OSi(OtBu)3]4− with outer-sphere [([12]crown-4)2Li]+ cations, and hydroxides {HOM[OSi(OtBu)3]3} with pendant [([12]crown-4)Li]+ cations. These molecular models were characterized by single-crystal X-ray diffraction, vibrational spectroscopy, mass spectrometry and NMR spectroscopy. Upon treatment of monomeric [([12]crown-4)Li]{HOM[OSi(OtBu)3]3} complexes with benzyl alcohol, benzyloxide complexes were formed, modeling a possible pathway for the formation of active sites for Meerwin–Ponndorf–Verley (MPV) transfer hydrogenations with Al/Ga-doped silica catalysts. 相似文献
118.
Fangyan Liu Biao Wang Prof. Dr. Xiaolong Liu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(6):1955-1960
Understanding of crystallization mechanisms of molecular sieves is driven by the broad range of usefulness and unique properties they possess. It is still difficult to obtain information related to the crystallization mechanism of molecular sieves, partly because the materials are generally prepared under hydrothermal conditions and the whole reaction happens in the “black box” autoclave. In this work, 2D 1H DQ-SQ NMR results clearly demonstrate that it is not only the electrostatic interactions between organic structure-directing agents (OSDAs) and the framework, but also the correlation among OSDAs playing the dominant structural directing roles during the crystallization process. Our fundamental understanding of the crystallization mechanism of molecular sieves could be of great value to design and synthesize new molecular sieves with desirable structural properties. 相似文献
119.
Jörg Wolfram Anselm Fischer Andreas Brenig Dr. Daniel Klose Prof. Dr. Jeroen Anton van Bokhoven Dr. Vitaly L. Sushkevich Prof. Dr. Gunnar Jeschke 《Angewandte Chemie (International ed. in English)》2023,62(34):e202303574
Cu-exchanged mordenite (MOR) is a promising material for partial CH4 oxidation. The structural diversity of Cu species within MOR makes it difficult to identify the active Cu sites and to determine their redox and kinetic properties. In this study, the Cu speciation in Cu-MOR materials with different Cu loadings has been determined using operando electron paramagnetic resonance (EPR) and operando ultraviolet-visible (UV/Vis) spectroscopy as well as in situ photoluminescence (PL) and Fourier-transform infrared (FTIR) spectroscopy. A novel pathway for CH4 oxidation involving paired [CuOH]+ and bare Cu2+ species has been identified. The reduction of bare Cu2+ ions facilitated by adjacent [CuOH]+ demonstrates that the frequently reported assumption of redox-inert Cu2+ centers does not generally apply. The measured site-specific reaction kinetics show that dimeric Cu species exhibit a faster reaction rate and a higher apparent activation energy than monomeric Cu2+ active sites highlighting their difference in the CH4 oxidation potential. 相似文献
120.
沸石基纳米材料的水热分散法制备及其发光 总被引:4,自引:0,他引:4
用水热分散法,通过进行分步化学反应,在沸石分子筛的孔道中简便有效地制备了沸石基纳米发光材料.样品的发光表现出纳米粒子的量子尺寸效应 相似文献