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1.
Direct Detection of Supramolecular Reaction Centers in the Methanol‐to‐Olefins Conversion over Zeolite H‐ZSM‐5 by 13C–27Al Solid‐State NMR Spectroscopy
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Dr. Chao Wang Dr. Qiang Wang Prof. Jun Xu Dr. Guodong Qi Pan Gao Weiyu Wang Yunyun Zou Dr. Ningdong Feng Dr. Xiaolong Liu Prof. Feng Deng 《Angewandte Chemie (International ed. in English)》2016,55(7):2507-2511
Hydrocarbon‐pool chemistry is important in methanol to olefins (MTO) conversion on acidic zeolite catalysts. The hydrocarbon‐pool (HP) species, such as methylbenzenes and cyclic carbocations, confined in zeolite channels during the reaction are essential in determining the reaction pathway. Herein, we experimentally demonstrate the formation of supramolecular reaction centers composed of organic hydrocarbon species and the inorganic zeolite framework in H‐ZSM‐5 zeolite by advanced 13C–27Al double‐resonance solid‐state NMR spectroscopy. Methylbenzenes and cyclic carbocations located near Brønsted acid/base sites form the supramolecular reaction centers in the zeolite channel. The internuclear spatial interaction/proximity between the 13C nuclei (associated with HP species) and the 27Al nuclei (associated with Brønsted acid/base sites) determines the reactivity of the HP species. The closer the HP species are to the zeolite framework Al, the higher their reactivity in the MTO reaction. 相似文献
2.
New Insight into the Hydrocarbon‐Pool Chemistry of the Methanol‐to‐Olefins Conversion over Zeolite H‐ZSM‐5 from GC‐MS,Solid‐State NMR Spectroscopy,and DFT Calculations
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Dr. Anmin Zheng Dr. Jun Xu Dr. Qiang Wang Pan Gao Guodong Qi Prof. Yanjun Gong Prof. Dr. Feng Deng 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(39):12432-12443
Over zeolite H‐ZSM‐5, the aromatics‐based hydrocarbon‐pool mechanism of methanol‐to‐olefins (MTO) reaction was studied by GC‐MS, solid‐state NMR spectroscopy, and theoretical calculations. Isotopic‐labeling experimental results demonstrated that polymethylbenzenes (MBs) are intimately correlated with the formation of olefin products in the initial stage. More importantly, three types of cyclopentenyl cations (1,3‐dimethylcyclopentenyl, 1,2,3‐trimethylcyclopentenyl, and 1,3,4‐trimethylcyclopentenyl cations) and a pentamethylbenzenium ion were for the first time identified by solid‐state NMR spectroscopy and DFT calculations under both co‐feeding ([13C6]benzene and methanol) conditions and typical MTO working (feeding [13C]methanol alone) conditions. The comparable reactivity of the MBs (from xylene to tetramethylbenzene) and the carbocations (trimethylcyclopentenyl and pentamethylbenzium ions) in the MTO reaction was revealed by 13C‐labeling experiments, evidencing that they work together through a paring mechanism to produce propene. The paring route in a full aromatics‐based catalytic cycle was also supported by theoretical DFT calculations. 相似文献
3.
Frontispiece: New Insight into the Hydrocarbon‐Pool Chemistry of the Methanol‐to‐Olefins Conversion over Zeolite H‐ZSM‐5 from GC‐MS,Solid‐State NMR Spectroscopy,and DFT Calculations
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Dr. Anmin Zheng Dr. Jun Xu Dr. Qiang Wang Pan Gao Guodong Qi Prof. Yanjun Gong Prof. Dr. Feng Deng 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(39)
4.
Experimental Evidence on the Formation of Ethene through Carbocations in Methanol Conversion over H‐ZSM‐5 Zeolite
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Chao Wang Xianfeng Yi Prof. Dr. Jun Xu Dr. Guodong Qi Pan Gao Weiyu Wang Dr. Yueying Chu Dr. Qiang Wang Dr. Ningdong Feng Dr. Xiaolong Liu Dr. Anmin Zheng Prof. Dr. Feng Deng 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(34):12061-12068
The methanol to olefins conversion over zeolite catalysts is a commercialized process to produce light olefins like ethene and propene but its mechanism is not well understood. We herein investigated the formation of ethene in the methanol to olefins reaction over the H‐ZSM‐5 zeolite. Three types of ethylcyclopentenyl carbocations, that is, the 1‐methyl‐3‐ethylcyclopentenyl, the 1,4‐dimethyl‐3‐ethylcyclopentenyl, and the 1,5‐dimethyl‐3‐ethylcyclopentenyl cation were unambiguously identified under working conditions by both solid‐state and liquid‐state NMR spectroscopy as well as GC‐MS analysis. These carbocations were found to be well correlated to ethene and lower methylbenzenes (xylene and trimethylbenzene). An aromatics‐based paring route provides rationale for the transformation of lower methylbenzenes to ethene through ethylcyclopentenyl cations as the key hydrocarbon‐pool intermediates. 相似文献
5.
Yuxiang Chen Ke Gong Feng Jiao Xiulian Pan Guangjin Hou Rui Si Xinhe Bao 《Angewandte Chemie (International ed. in English)》2020,59(16):6529-6534
Despite significant progress achieved in Fischer–Tropsch synthesis (FTS) technology, control of product selectivity remains a challenge in syngas conversion. Herein, we demonstrate that Zn2+‐ion exchanged ZSM‐5 zeolite steers syngas conversion selectively to ethane with its selectivity reaching as high as 86 % among hydrocarbons (excluding CO2) at 20 % CO conversion. NMR spectroscopy, X‐ray absorption spectroscopy, and X‐ray fluorescence indicate that this is likely attributed to the highly dispersed Zn sites grafted on ZSM‐5. Quasi‐in‐situ solid‐state NMR, obtained by quenching the reaction in liquid N2, detects C2 species such as acetyl (‐COCH3) bonding with an oxygen, ethyl (‐CH2CH3) bonding with a Zn site, and epoxyethane molecules adsorbing on a Zn site and a Brønsted acid site of the catalyst, respectively. These species could provide insight into C?C bond formation during ethane formation. Interestingly, this selective reaction pathway toward ethane appears to be general because a series of other Zn2+‐ion exchanged aluminosilicate zeolites with different topologies (for example, SSZ‐13, MCM‐22, and ZSM‐12) all give ethane predominantly. By contrast, a physical mixture of ZnO‐ZSM‐5 favors formation of hydrocarbons beyond C3+. These results provide an important guide for tuning the product selectivity in syngas conversion. 相似文献
6.
Back Cover: Direct Detection of Supramolecular Reaction Centers in the Methanol‐to‐Olefins Conversion over Zeolite H‐ZSM‐5 by 13C–27Al Solid‐State NMR Spectroscopy (Angew. Chem. Int. Ed. 7/2016)
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Dr. Chao Wang Dr. Qiang Wang Prof. Jun Xu Dr. Guodong Qi Pan Gao Weiyu Wang Yunyun Zou Dr. Ningdong Feng Dr. Xiaolong Liu Prof. Feng Deng 《Angewandte Chemie (International ed. in English)》2016,55(7):2602-2602
7.
Alkane Activation Initiated by Hydride Transfer: Co‐conversion of Propane and Methanol over H‐ZSM‐5 Zeolite
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Si‐Min Yu Dr. Jian‐Feng Wu Chong Liu Dr. Wei Liu Prof. Dr. Shi Bai Dr. Jun Huang Prof. Dr. Wei Wang 《Angewandte Chemie (International ed. in English)》2015,54(25):7363-7366
Co‐conversion of alkane with another reactant over zeolite catalysts has emerged as a new approach to the long‐standing challenge of alkane transformation. With the aid of solid‐state NMR spectroscopy and GC‐MS analysis, it was found that the co‐conversion of propane and methanol can be readily initiated by hydride transfer at temperatures of ≥449 K over the acidic zeolite H‐ZSM‐5. The formation of 13C‐labeled methane and singly 13C‐labeled n‐butanes in selective labeling experiments provided the first evidence for the initial hydride transfer from propane to surface methoxy intermediates. The results not only provide new insight into carbocation chemistry of solid acids, but also shed light on the low‐temperature transformation of alkanes for industrial applications. 相似文献
8.
Identification of tert‐Butyl Cations in Zeolite H‐ZSM‐5: Evidence from NMR Spectroscopy and DFT Calculations
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Dr. Weili Dai Prof.Dr. Chuanming Wang Dr. Xianfeng Yi Prof. Dr. Anmin Zheng Prof. Dr. Landong Li Prof. Dr. Guangjun Wu Prof. Dr. Naijia Guan Prof. Dr. Zaiku Xie Dipl.‐Chem. Michael Dyballa Prof. Dr. Michael Hunger 《Angewandte Chemie (International ed. in English)》2015,54(30):8783-8786
Experimental evidence for the presence of tert‐butyl cations, which are important intermediates in acid‐catalyzed heterogeneous reactions, on solid acids has still not been provided to date. By combining density functional theory (DFT) calculations with 1H/13C magic‐angle‐spinning NMR spectroscopy, the tert‐butyl cation was successfully identified on zeolite H‐ZSM‐5 upon conversion of isobutene by capturing this intermediate with ammonia. 相似文献
9.
Extra‐Framework Aluminum‐Assisted Initial C−C Bond Formation in Methanol‐to‐Olefins Conversion on Zeolite H‐ZSM‐5
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Dr. Chao Wang Dr. Yueying Chu Prof. Dr. Jun Xu Dr. Qiang Wang Dr. Guodong Qi Pan Gao Xue Zhou Prof. Dr. Feng Deng 《Angewandte Chemie (International ed. in English)》2018,57(32):10197-10201
Surface methoxy species bound to an extra‐framework Al (SMS‐EFAL) was unambiguously identified by advanced 13C‐{27Al} double‐resonance solid‐state NMR technique in the methanol‐to‐olefins reaction on H‐ZSM‐5 zeolite. The high reactivity of the SMS‐EFAL leads to the formation of surface ethoxy species and ethanol as the key intermediates for ethene generation in the early reaction stage. A direct route for the initial C?C bond formation in ethene was proposed and corroborated by density functional theory calculations. 相似文献
10.
Following Solid‐Acid‐Catalyzed Reactions by MAS NMR Spectroscopy in Liquid Phase—Zeolite‐Catalyzed Conversion of Cyclohexanol in Water
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Aleksei Vjunov Mary Y. Hu Dr. Ju Feng Dr. Donald M. Camaioni Dr. Donghai Mei Dr. Jian Z. Hu Dr. Chen Zhao Prof. Dr. Johannes A. Lercher 《Angewandte Chemie (International ed. in English)》2014,53(2):479-482
A microautoclave magic angle spinning NMR rotor is developed enabling in situ monitoring of solid–liquid–gas reactions at high temperatures and pressures. It is used in a kinetic and mechanistic study of the reactions of cyclohexanol on zeolite HBEA in 130 °C water. The 13C spectra show that dehydration of 1‐13C‐cyclohexanol occurs with significant migration of the hydroxy group in cyclohexanol and the double bond in cyclohexene with respect to the 13C label. A simplified kinetic model shows the E1‐type elimination fully accounts for the initial rates of 1‐13C‐cyclohexanol disappearance and the appearance of the differently labeled products, thus suggesting that the cyclohexyl cation undergoes a 1,2‐hydride shift competitive with rehydration and deprotonation. Concurrent with the dehydration, trace amounts of dicyclohexyl ether are observed, and in approaching equilibrium, a secondary product, cyclohexyl‐1‐cyclohexene is formed. Compared to phosphoric acid, HBEA is shown to be a more active catalyst exhibiting a dehydration rate that is 100‐fold faster per proton. 相似文献
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12.
Hexameric Capsules Studied by Magic Angle Spinning Solid‐State NMR Spectroscopy: Identifying Solvent Molecules in Pyrogallol[4]arene Capsules
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Dr. Liat Avram Dr. Amir Goldbourt Prof. Dr. Yoram Cohen 《Angewandte Chemie (International ed. in English)》2016,55(3):904-907
Powders of pyrogallol[4]arene hexamers were produced by evaporation from organic solvents and were studied, for the first time, by magic angle spinning solid‐state NMR (MAS ssNMR). Evaporation selectively removed non‐encapsulated solvent molecules leaving stable hexameric capsules encapsulating solvent molecules. After exposure of the powder to solvent vapors, 1H/13C heteronuclear correlation MAS ssNMR experiments were used to assign the signals of the external and encapsulated solvent molecules. The formed capsules were stable for months and the process of solvent encapsulation was reversible. According to the ssNMR experiments, the encapsulated solvent molecules occupy different sites and those sites differ in their mobility. The presented approach paves the way for studying guest exchange, guest affinity, and gas storage in hexamers of this type in the solid state. 相似文献
13.
Analysis of vaporous contaminants including low‐volatility analytes permeating textiles at room temperature using headspace solid‐phase microextraction GC–MS
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W. Bruce Salter Derek D. Lovingood William Creasy Jeffery R. Owens 《Surface and interface analysis : SIA》2016,48(1):47-50
Detection of toxic vapors permeating textiles is an important measure of the efficacy of a protective garment. Here, we demonstrate a method to detect and analyze contaminant vapors as they permeate through cotton textiles. Specifically, we show how this method can be improved upon by the incorporation of solid‐phase microextraction into the sampling process, thereby allowing low‐volatility analytes to be sampled at room temperature without significantly influencing the concentration of the contaminant in the headspace. Furthermore, this technique can be extended to other applications in the development of barrier materials as it lends itself to kinetics as well as direct comparison of materials' total chemical permeation. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
14.
Consuelo Sánchez‐Brunete Ester Miguel José L. Tadeo 《Journal of separation science》2009,32(1):109-117
A method for the determination of 14 polybrominated diphenyl ethers (PBDEs) in sludge from wastewater treatment plants is presented. PBDEs were extracted by matrix solid‐phase dispersion assisted by sonication and determined by isotope dilution gas chromatography with electron impact mass spectrometric detection in the selected ion monitoring mode, using labelled 13C‐PBDEs as internal standards. The limits of detection and quantification for the tri‐ to hepta‐BDEs were in the range of 0.05 to 0.5 ng/g dry weight and 0.15 to 1.8 ng/g dry weight, respectively, and 1.6 ng/g dry weight and 5.6 ng/g dry weight for deca‐BDE‐209. The proposed analytical method was applied to determine PBDE levels in sewage sludge samples collected from 19 water treatment plants located in the province of Madrid (Spain). In all of the examined samples, BDE‐100 and BDE‐154 were the main compounds found with a mean concentration of 3.9 and 2.0 ng/g, respectively. PBDEs were detected in all of the samples, and their total concentrations not considering BDE‐209 were between 3.9 and 23.0 ng/g dry weight. The dominant PBDE congener in sewage sludge was BDE‐209, which constituted 38.7 to 97.3% of the total, and showed concentration levels ranging from 8.1 to 717.2 ng/g dry weight. 相似文献
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16.
Yi Cai Min Zhao Zhibo Guan Xue Han Miao Wang Chunjie Zhao 《Biomedical chromatography : BMC》2019,33(10)
Semen descurainiae oil (SDO) is an important traditional Chinese medicine that was recently discovered to have the function of reducing blood lipids. Metabolomics analyses of plasma, liver and kidney in rats were performed using 1H‐NMR and LC–MS to illuminate the lower blood lipid concentration effect of SDO, and niacin was considered as the active control. The measure of total cholesterol (TC) and low‐density‐lipoprotein cholesterol (LDL‐C) in plasma showed that SDO treatment decreased significantly the content of TC and LDL‐C. An orthogonal partial least squares–discriminant analysis approach was applied to identify the different metabolic profiles of plasma, liver and kidney in rats and to detect related potential biomarkers. The results suggested that the metabolic profiles of the control group and hyperlipidemia group showed significant difference and the SDO and niacin group had effective anti‐hyperlipidemia function. The biomarkers primarily concern lipid metabolism, amino acid metabolism and glycometabolism, and the change in biomarkers indicated that hyperlipidemia could cause the unbalance of these metabolic pathways in vivo. SDO reduced blood lipids by repairing amino acid and lipid metabolism. 相似文献
17.
Reconstitution of the Cytb5–CytP450 Complex in Nanodiscs for Structural Studies using NMR Spectroscopy
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Meng Zhang Rui Huang Dr. Rose Ackermann Dr. Sang‐Choul Im Prof. Lucy Waskell Prof. Anna Schwendeman Prof. Ayyalusamy Ramamoorthy 《Angewandte Chemie (International ed. in English)》2016,55(14):4497-4499
Cytochrome P450s (P450s) are a superfamily of enzymes responsible for the catalysis of a wide range of substrates. Dynamic interactions between full‐length membrane‐bound P450 and its redox partner cytochrome b5 (cytb5) have been found to be important for the enzymatic activity of P450. However, the stability of the circa 70 kDa membrane‐bound complex in model membranes renders high‐resolution structural NMR studies particularly difficult. To overcome these challenges, reconstitution of the P450–cytb5 complex in peptide‐based nanodiscs, containing no detergents, has been demonstrated, which are characterized by size exclusion chromatography and NMR spectroscopy. In addition, NMR experiments are used to identify the binding interface of the P450–cytb5 complex in the nanodisc. This is the first successful demonstration of a protein–protein complex in a nanodisc using NMR structural studies and should be useful to obtain valuable structural information on membrane‐bound protein complexes. 相似文献
18.
Qinhui Wang Tao Yan Wei Jiang Na Hu Song Zhang Peng Yang Wenjuan Zhang Lei Shi Linna Liu 《Biomedical chromatography : BMC》2019,33(10)
The herb couple has special clinical significance in reducing the toxicity and increasing the efficacy of drugs. The combination of Radix Angelicae Dahuricae (Baizhi, BZ) and Rhizoma Chuanxiong (ChuanXiong, CX) is a traditional herb couple. The combination performs better than the CX extract alone in the treatment of migraine and has been used for thousands of years. However, the specific compatibility mechanisms are still unclear. Ligustilide, dl ‐3‐n‐butylphthalide and senkyunolide A are the major active ingredients in CX and BZ–CX decoction. However, a comprehensive study of the pharmacokinetics of CX has not been carried out. A gas chromatography–mass spectroscopy (GC–MS) method with high selectivity, sensitivity and accuracy was developed. An SH‐Rxi‐5Sil (30 m × 0.25 mm i.d., and 0.25 μm film thickness) column was employed in the GC separation. Selectivity, linearity, precision, accuracy, recovery, matrix effect and stability were used to validate the current GC–MS method. Using the validated method, this is the first time to study on the comparative pharmacokinetics of ligustilide, dl ‐3‐n‐butylphthalide and senkyunolide A from CX alone and BZ–CX decoction in rat plasma. The pharmacokinetic parameters (Cmax, Tmax, T1/2, AUC0–t, AUC0–∞ and CLz/F) of all of the detected ingredients showed significant differences between the two groups (P < 0.05). The results are helpful for further investigation of the compatibility mechanism of BZ–CX decoction. 相似文献
19.
《Journal of mass spectrometry : JMS》2017,52(7):417-426
An Open Probe inlet was combined with a low thermal mass ultra‐fast gas chromatograph (GC), in‐vacuum electron ionization ion source and a mass spectrometer (MS) of GC–MS for obtaining real‐time analysis with separation. The Open Probe enables ambient sampling via sample vaporization in an oven that is open to room air, and the ultra‐fast GC provides ~30‐s separation, while if no separation is required, it can act as a transfer line with 2 to 3‐s sample transfer time. Sample analysis is as simple as touching the sample, pushing the sample holder into the Open Probe oven and obtaining the results in 30 s. The Open Probe fast GC was mounted on a standard Agilent 7890 GC that was coupled with an Agilent 5977A MS. Open Probe fast GC–MS provides real‐time analysis combined with GC separation and library identification, and it uses the low‐cost MS of GC–MS. The operation of Open Probe fast GC–MS is demonstrated in the 30‐s separation and 50‐s full analysis cycle time of tetrahydrocannabinol and cannabinol in Cannabis flower, sub 1‐min analysis of trace trinitrotoluene transferred from a finger onto a glass surface, vitamin E in canola oil, sterols in olive oil, polybrominated flame retardants in plastics, alprazolam in Xanax drug pill and free fatty acids and cholesterol in human blood. The extrapolated limit of detection for pyrene is <1 fg, but the concentration is too high and the software noise calculation is untrustworthy. The broad range of compounds amenable for analysis is demonstrated in the analysis of reserpine. The possible use with alternate standard GC–MS and Open Probe fast GC–MS is demonstrated in the analysis of heroin in its street drug powder. The use of Open Probe with the fast GC acting as a transfer line is demonstrated in <10‐s analysis without separation of ibuprofen and estradiol. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
20.
Sugar–Edge Interactions in a DNA–RNA G‐Quadruplex: Evidence of Sequential C−H⋅⋅⋅O Hydrogen Bonds Contributing to RNA Quadruplex Folding
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Jonathan Dickerhoff Dr. Bettina Appel Prof. Dr. Sabine Müller Prof. Dr. Klaus Weisz 《Angewandte Chemie (International ed. in English)》2016,55(48):15162-15165
DNA G‐quadruplexes were systematically modified by single riboguanosine (rG) substitutions at anti‐dG positions. Circular dichroism and NMR experiments confirmed the conservation of the native quadruplex topology for most of the DNA–RNA hybrid structures. Changes in the C8 NMR chemical shift of guanosines following rG substitution at their 3′‐side within the quadruplex core strongly suggest the presence of C8?H???O hydrogen‐bonding interactions with the O2′ position of the C2′‐endo ribonucleotide. A geometric analysis of reported high‐resolution structures indicates that such interactions are a more general feature in RNA quadruplexes and may contribute to the observed preference for parallel topologies. 相似文献