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1.
Bridging the Gap between the Direct and Hydrocarbon Pool Mechanisms of the Methanol‐to‐Hydrocarbons Process 下载免费PDF全文
Dr. Abhishek Dutta Chowdhury Alessandra Lucini Paioni Dr. Klaartje Houben Dr. Gareth T. Whiting Prof. Dr. Marc Baldus Prof. Dr. Bert M. Weckhuysen 《Angewandte Chemie (International ed. in English)》2018,57(27):8095-8099
After a prolonged effort over many years, the route for the formation of a direct carbon?carbon (C?C) bond during the methanol‐to‐hydrocarbon (MTH) process has very recently been unveiled. However, the relevance of the “direct mechanism”‐derived molecules (that is, methyl acetate) during MTH, and subsequent transformation routes to the conventional hydrocarbon pool (HCP) species, are yet to be established. This important piece of the MTH chemistry puzzle is not only essential from a fundamental perspective, but is also important to maximize catalytic performance. The MTH process was probed over a commercially relevant H‐SAPO‐34 catalyst, using a combination of advanced solid‐state NMR spectroscopy and operando UV/Vis diffuse reflectance spectroscopy coupled to an on‐line mass spectrometer. Spectroscopic evidence is provided for the formation of (olefinic and aromatic) HCP species, which are indeed derived exclusively from the direct C?C bond‐containing acetyl group of methyl acetate. New mechanistic insights have been obtained from the MTH process, including the identification of hydrocarbon‐based co‐catalytic organic reaction centers. 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 下载免费PDF全文
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.
Mustafa alayan Alessandra Lucini Paioni Edy Abou‐Hamad Genrikh Shterk Alexey Pustovarenko Marc Baldus Abhishek Dutta Chowdhury Jorge Gascon 《Angewandte Chemie (International ed. in English)》2020,59(38):16741-16746
Methane dehydroaromatization (MDA) is among the most challenging processes in catalysis science owing to the inherent harsh reaction conditions and fast catalyst deactivation. To improve this process, understanding the mechanism of the initial C?C bond formation is essential. However, consensus about the actual reaction mechanism is still to be achieved. In this work, using advanced magic‐angle spinning (MAS) solid‐state NMR spectroscopy, we study in detail the early stages of the reaction over a well‐dispersed Mo/H‐ZSM‐5 catalyst. Simultaneous detection of acetylene (i.e., presumably the direct C?C bond‐forming product from methane), methylidene, allenes, acetal, and surface‐formate species, along with the typical olefinic/aromatic species, allow us to conclude the existence of at least two independent C?H activation pathways. Moreover, this study emphasizes the significance of mobility‐dependent host–guest chemistry between an inorganic zeolite and its trapped organic species during heterogeneous catalysis. 相似文献
4.
Direct Detection of Supramolecular Reaction Centers in the Methanol‐to‐Olefins Conversion over Zeolite H‐ZSM‐5 by 13C–27Al Solid‐State NMR Spectroscopy 下载免费PDF全文
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
5.
Direct N‐Methylation Reaction Using DMSO as One‐Carbon Bridge: Convenient Access to Heterocycle‐Containing β‐Amino Ketones 下载免费PDF全文
Dr. Kai Sun Dr. Xin Wang Yongqing Jiang Yunhe Lv Prof. Liping Zhang Beibei Xiao Donghui Li Zhonghong Zhu Prof. Lin Liu 《化学:亚洲杂志》2015,10(3):536-539
A novel oxidative C? S bond cleavage reaction of DMSO for dual C? C and C? N bond formation is described. A series of acetyl heteroarenes could be selectively converted into the corresponding β‐amino ketones, which are frequently found in biologically active compounds and pharmaceuticals. DMSO acted in this reaction not only as the solvent but also as a one‐carbon bridge. 相似文献
6.
Effects of Coke Deposits on the Catalytic Performance of Large Zeolite H‐ZSM‐5 Crystals during Alcohol‐to‐Hydrocarbon Reactions as Investigated by a Combination of Optical Spectroscopy and Microscopy 下载免费PDF全文
Dr. Emily C. Nordvang Dr. Elena Borodina Dr. Javier Ruiz‐Martínez Prof. Dr. Rasmus Fehrmann Prof. Dr. Bert M. Weckhuysen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(48):17324-17335
The catalytic activity of large zeolite H‐ZSM‐5 crystals in methanol (MTO) and ethanol‐to‐olefins (ETO) conversions was investigated and, using operando UV/Vis measurements, the catalytic activity and deactivation was correlated with the formation of coke. These findings were related to in situ single crystal UV/Vis and confocal fluorescence micro‐spectroscopy, allowing the observation of the spatiotemporal formation of intermediates and coke species during the MTO and ETO conversions. It was observed that rapid deactivation at elevated temperatures was due to the fast formation of aromatics at the periphery of the H‐ZSM‐5 crystals, which are transformed into more poly‐aromatic coke species at the external surface, preventing the diffusion of reactants and products into and out of the H‐ZSM‐5 crystal. Furthermore, we were able to correlate the operando UV/Vis spectroscopy results observed during catalytic testing with the single crystal in situ results. 相似文献
7.
《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(31):9167-9171
In the past two decades, the reaction mechanism of C−C bond formation from either methanol or dimethyl ether (DME) in the methanol‐to‐hydrocarbons (MTH) process has been a highly controversial issue. Described here is the first observation of a surface methyleneoxy analogue, originating from the surface‐activated DME, by in situ solid‐state NMR spectroscopy, a species crucial to the first C−C bond formation in the MTH process. New insights into the first C−C bond formation were provided, thus suggesting DME/methanol activation and direct C−C bond formation by an interesting synergetic mechanism, involving C−H bond breakage and C−C bond coupling during the initial methanol reaction within the chemical environment of the zeolite catalyst. 相似文献
8.
Inherent Conformational Preferences of Ac‐Gln‐Gln‐NHBn: Sidechain Hydrogen Bonding Supports a β‐Turn in the Gas Phase 下载免费PDF全文
Dr. Patrick S. Walsh Karl N. Blodgett Carl McBurney Prof. Samuel H. Gellman Prof. Timothy S. Zwier 《Angewandte Chemie (International ed. in English)》2016,55(47):14618-14622
Gas‐phase single‐conformation spectroscopy is used to study Ac‐Gln‐Gln‐NHBn in order to probe the interplay between sidechain hydrogen bonding and backbone conformational preferences. This small, amide‐rich peptide offers many possibilities for backbone–backbone, sidechain–backbone, and sidechain–sidechain interactions. The major conformer observed experimentally features a type‐I β‐turn with a canonical 10‐membered ring C=O—H?N hydrogen bond between backbone amide groups. In addition, the C=O group of each Gln sidechain participates in a seven‐membered ring hydrogen bond with the backbone NH of the same residue. Thus, sidechain hydrogen‐bonding potential is satisfied in a manner that is consistent with and stabilizes the β‐turn secondary structure. This turn‐forming propensity may be relevant to pathogenic amyloid formation by polyglutamine segments in human proteins. 相似文献
9.
Yajun Zhao Yong Wang Xingping Zhou Zhigang Xue Xianhong Wang Xiaolin Xie Rinaldo Poli 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(40):14449-14456
Switchable polymerization provides the opportunity to regulate polymer sequence and structure in a one‐pot process from mixtures of monomers. Herein we report the use of O2 as an external stimulus to switch the polymerization mechanism from the radical polymerization of vinyl monomers mediated by (Salen)CoIII?R [Salen=N,N′‐bis(3,5‐di‐tert‐butylsalicylidene)‐1,2‐cyclohexanediamine; R=alkyl] to the ring‐opening copolymerization (ROCOP) of CO2/epoxides. Critical to this process is unprecedented monooxygen insertion into the Co?C bond, as rationalized by DFT calculations, leading to the formation of (Salen)CoIII?O?R as an active species to initiate ROCOP. Diblock poly(vinyl acetate)‐b‐polycarbonate could be obtained by ROCOP of CO2/epoxides with preactivation of (Salen)Co end‐capped poly(vinyl acetate). Furthermore, a poly(vinyl acetate)‐b‐poly(methyl acrylate)‐b‐polycarbonate triblock copolymer was successfully synthesized by a (Salen)cobalt‐mediated sequential polymerization with an O2‐triggered switch in a one‐pot process. 相似文献
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11.
Formation Mechanism of the First Carbon–Carbon Bond and the First Olefin in the Methanol Conversion into Hydrocarbons 下载免费PDF全文
Dr. Yue Liu Dr. Sebastian Müller Dr. Daniel Berger Dr. Jelena Jelic Prof. Dr. Karsten Reuter Dr. Markus Tonigold Dr. Maricruz Sanchez‐Sanchez Prof. Dr. Johannes A. Lercher 《Angewandte Chemie (International ed. in English)》2016,55(19):5723-5726
The elementary reactions leading to the formation of the first carbon–carbon bond during early stages of the zeolite‐catalyzed methanol conversion into hydrocarbons were identified by combining kinetics, spectroscopy, and DFT calculations. The first intermediates containing a C?C bond are acetic acid and methyl acetate, which are formed through carbonylation of methanol or dimethyl ether even in presence of water. A series of acid‐catalyzed reactions including acetylation, decarboxylation, aldol condensation, and cracking convert those intermediates into a mixture of surface bounded hydrocarbons, the hydrocarbon pool, as well as into the first olefin leaving the catalyst. This carbonylation based mechanism has an energy barrier of 80 kJ mol?1 for the formation of the first C?C bond, in line with a broad range of experiments, and significantly lower than the barriers associated with earlier proposed mechanisms. 相似文献
12.
Hannes Kulla Sebastian Haferkamp Irina Akhmetova Mathias Röllig Dr. Christiane Maierhofer Prof. Dr. Klaus Rademann Dr. Franziska Emmerling 《Angewandte Chemie (International ed. in English)》2018,57(20):5930-5933
We present an in situ triple coupling of synchrotron X‐ray diffraction with Raman spectroscopy, and thermography to study milling reactions in real time. This combination of methods allows a correlation of the structural evolution with temperature information. The temperature information is crucial for understanding both the thermodynamics and reaction kinetics. The reaction mechanisms of three prototypical mechanochemical syntheses, a cocrystal formation, a C?C bond formation (Knoevenagel condensation), and the formation of a manganese‐phosphonate, were elucidated. Trends in the temperature development during milling are identified. The heat of reaction and latent heat of crystallization of the product contribute to the overall temperature increase. A decrease in temperature occurs via release of, for example, water as a by‐product. Solid and liquid intermediates are detected. The influence of the mechanical impact could be separated from temperature effects caused by the reaction. 相似文献
13.
Activation of α‐Diazocarbonyls by Organic Catalysts: Diazo Group Acting as a Strong N‐Terminal Electrophile 下载免费PDF全文
Lei Li Jia‐Jia Chen Yi‐Jin Li Xiu‐Bin Bu Qun Liu Yu‐Long Zhao 《Angewandte Chemie (International ed. in English)》2015,54(41):12107-12111
For the first time α‐diazocarbonyls have been used as highly active N‐terminal electrophiles in the presence of bicyclic amidine catalysts. The C? N bond‐forming reactions of active methylene compounds as C nucleophiles with α‐diazocarbonyls as N‐terminal electrophiles proceed quickly under ambient conditions, in the presence of 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU), because of the formation of the reactive N‐terminal electrophilic intermediates. DBU activates both the active methylene and α‐diazocarbonyl. Importantly, this reaction is general for both active methylenes and α‐diazocarbonyls, and the activation mode will lead to new synthetic applications of α‐diazocarbonyls. 相似文献
14.
Prof. Susana Blanco Pablo Pinacho Prof. Juan Carlos López 《Angewandte Chemie (International ed. in English)》2016,55(32):9331-9335
The rotational spectrum of formamide2–H2O formed in a supersonic jet has been characterized by Fourier‐transform microwave spectroscopy. This adduct provides a simple model of water‐mediated interaction involving the amide linkages, as occur in protein folding or amide‐association processes, showing the interplay between self‐association and solvation. Mono‐substituted 13C, 15N, 18O, and 2H isotopologues have been observed and their data used to investigate the structure. The adduct forms an almost planar three‐body sequential cycle. The two formamide molecules link on one side through an N?H???O hydrogen bond and on the other side through a water‐mediated interaction with the formation of C=O???H?O and O???H?N hydrogen bonds. The analysis of the quadrupole coupling effects of two 14N‐nuclei reveals the subtle inductive forces associated to cooperative hydrogen bonding. These forces are involved in the changes in the C=O and C?N bond lengths with respect to pure formamide. 相似文献
15.
A DFT Study on the Conversion of Aryl Iodides to Alkyl Iodides: Reductive Elimination of R−I from Alkylpalladium Iodide Complexes with Accessible β‐Hydrogens 下载免费PDF全文
Wei Hao Junnian Wei Yue Chi Prof. Dr. Patrick J. Walsh Prof. Dr. Zhenfeng Xi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(10):3422-3429
DFT calculations have been performed on the palladium‐catalyzed carboiodination reaction. The reaction involves oxidative addition, alkyne insertion, C?N bond cleavage, and reductive elimination. For the alkylpalladium iodide intermediate, LiOtBu stabilizes the intermediate in non‐polar solvents, thus promoting reductive elimination and preventing β‐hydride elimination. The C?N bond cleavage process was explored and the computations show that PPh3 is not bound to the Pd center during this step. Experimentally, it was demonstrated that LiOtBu is not necessary for the oxidative addition, alkyne insertion, or C?N bond cleavage steps, lending support to the conclusions from the DFT calculations. The turnover‐limiting steps were found to be C?N bond cleavage and reductive elimination, whereas oxidative addition, alkyne insertion, and formation of the indole ring provide the driving force for the reaction. 相似文献
16.
Olefin Cyclopropanation by Radical Carbene Transfer Reactions Promoted by Cobalt(II)/Porphyrinates: Active‐Metal‐Template Synthesis of [2]Rotaxanes 下载免费PDF全文
Arthur F. P. Alcântara Liniquer A. Fontana Vitor H. Rigolin Yuri F. S. Andrade Dr. Marcos A. Ribeiro Prof. Wdeson P. Barros Prof. Catia Ornelas Prof. Jackson D. Megiatto Jr. 《Angewandte Chemie (International ed. in English)》2018,57(29):8979-8983
A CoII/porphyrinate‐based macrocycle in the presence of a 3,5‐diphenylpyridine axial ligand functions as an endotopic ligand to direct the assembly of [2]rotaxanes from diazo and styrene half‐threads, by radical‐carbene‐transfer reactions, in excellent 95 % yield. The method reported herein applies the active‐metal‐template strategy to include radical‐type activation of ligands by the metal‐template ion during the organometallic process which ultimately yields the mechanical bond. A careful quantitative analysis of the product distribution afforded from the rotaxane self‐assembly reaction shows that the CoII/porphyrinate subunit is still active after formation of the mechanical bond and, upon coordination of an additional diazo half‐thread derivative, promotes a novel intercomponent C?H insertion reaction to yield a new rotaxane‐like species. This unexpected intercomponent C?H insertion illustrates the distinct reactivity brought to the CoII/porphyrinate catalyst by the mechanical bond. 相似文献
17.
Qingyun Qian Dr. Javier Ruiz‐Martínez Prof. Dr. Mohamed Mokhtar Prof. Dr. Abdullah M. Asiri Prof. Dr. Shaeel A. Al‐Thabaiti Prof. Dr. Suliman N. Basahel Hendrik E. van der Bij Dr. Jan Kornatowski Prof. Dr. Bert M. Weckhuysen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(34):11204-11215
The formation of hydrocarbon pool (HCP) species during methanol‐to‐olefin (MTO) and ethanol‐to‐olefin (ETO) processes have been studied on individual micron‐sized SAPO‐34 crystals with a combination of in situ UV/Vis, confocal fluorescence, and synchrotron‐based IR microspectroscopic techniques. With in situ UV/Vis microspectroscopy, the intensity changes of the λ=400 nm absorption band, ascribed to polyalkylated benzene (PAB) carbocations, have been monitored and fitted with a first‐order kinetics at low reaction temperatures. The calculated activation energy (Ea) for MTO, approximately 98 kJ mol?1, shows a strong correlation with the theoretical values for the methylation of aromatics. This provides evidence that methylation reactions are the rate‐determining steps for the formation of PAB. In contrast for ETO, the Ea value is approximately 60 kJ mol?1, which is comparable to the Ea values for the condensation of light olefins into aromatics. Confocal fluorescence microscopy demonstrates that during MTO the formation of the initial HCP species are concentrated in the outer rim of the SAPO‐34 crystal when the reaction temperature is at 600 K or lower, whereas larger HCP species are gradually formed inwards the crystal at higher temperatures. In the case of ETO, the observed egg‐white distribution of HCP at 509 K suggests that the ETO process is kinetically controlled, whereas the square‐shaped HCP distribution at 650 K is indicative of a diffusion‐controlled process. Finally, synchrotron‐based IR microspectroscopy revealed a higher degree of alkylation for aromatics for MTO as compared to ETO, whereas high reaction temperatures favor dealkylation processes for both the MTO and ETO processes. 相似文献
18.
One‐Pot Tandem Photoredox and Cross‐Coupling Catalysis with a Single Palladium Carbodicarbene Complex 下载免费PDF全文
Yu‐Cheng Hsu Vincent C.‐C. Wang Ka‐Chun Au‐Yeung Chung‐Yu Tsai Chun‐Chi Chang Bo‐Chao Lin Prof. Yi‐Tsu Chan Prof. Chao‐Ping Hsu Prof. Glenn P. A. Yap Prof. Titel Jurca Prof. Tiow‐Gan Ong 《Angewandte Chemie (International ed. in English)》2018,57(17):4622-4626
The combination of conventional transition‐metal‐catalyzed coupling (2 e? process) and photoredox catalysis (1 e? process) has emerged as a powerful approach to catalyze difficult cross‐coupling reactions under mild reaction conditions. Reported is a palladium carbodicarbene (CDC) complex that mediates both a Suzuki–Miyaura coupling and photoredox catalysis for C?N bond formation upon visible‐light irradiation. These two catalytic pathways can be combined to promote both conventional transition‐metal‐catalyzed coupling and photoredox catalysis to mediate C?H arylation under ambient conditions with a single catalyst in an efficient one‐pot process. 相似文献
19.
A Single‐Molecule‐Level Mechanistic Study of Pd‐Catalyzed and Cu‐Catalyzed Homocoupling of Aryl Bromide on an Au(111) Surface 下载免费PDF全文
Dr. Jinne Adisoejoso Tao Lin Xue Song Shang Ke Ji Shi Aditi Gupta Prof. Dr. Pei Nian Liu Prof. Dr. Nian Lin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(14):4111-4116
On‐surface Pd‐ and Cu‐catalyzed C?C coupling reactions between phenyl bromide functionalized porphyrin derivatives on an Au(111) surface have been investigated under ultra‐high vacuum conditions by using scanning tunneling microscopy and kinetic Monte Carlo simulations. We monitored the isothermal reaction kinetics by allowing the reaction to proceed at different temperatures. We discovered that the reactions catalyzed by Pd or Cu can be described as a two‐phase process that involves an initial activation followed by C?C bond formation. However, the distinctive reaction kinetics and the C?C bond‐formation yield associated with the two catalysts account for the different reaction mechanisms: the initial activation phase is the rate‐limiting step for the Cu‐catalyzed reaction at all temperatures tested, whereas the later phase of C?C formation is the rate‐limiting step for the Pd‐catalyzed reaction at high temperature. Analysis of rate constants of the Pd‐catalyzed reactions allowed us to determine its activation energy as (0.41±0.03) eV. 相似文献
20.
Synergic Effect of Active Sites in Zinc‐Modified ZSM‐5 Zeolites as Revealed by High‐Field Solid‐State NMR Spectroscopy 下载免费PDF全文
Dr. Guodong Qi Dr. Qiang Wang Prof. Jun Xu Dr. Julien Trébosc Prof. Olivier Lafon Dr. Chao Wang Prof. Jean‐Paul Amoureux Prof. Feng Deng 《Angewandte Chemie (International ed. in English)》2016,55(51):15826-15830
Understanding the nature of active sites in metal‐supported catalysts is of great importance towards establishing their structure–property relationships. The outstanding catalytic performance of metal‐supported catalysts is frequently ascribed to the synergic effect of different active sites, which is however not well spectroscopically characterized. Herein, we report the direct detection of surface Zn species and 1H–67Zn internuclear interaction between Zn2+ ions and Brønsted acid sites on Zn‐modified ZSM‐5 zeolites by high‐field solid‐state NMR spectroscopy. The observed promotion of C?H bond activation of methane is rationalized by the enhanced Brønsted acidity generated by synergic effects arising from the spatial proximity/interaction between Zn2+ ions and Brønsted acidic protons. The concentration of synergic active sites is determined by 1H–67Zn double‐resonance solid‐state NMR spectroscopy. 相似文献