A list of puns related to "Dehydrogenation"
Does anyone have an opinion about whether the "Dehydrogenation of 1,4-Butanediol (1,4-BD) to gamma-Butyrolactone (GBL)" is a better option than "Solvent free permanganate oxidations using (1,4-BD) to GBL" which sythesis requires the least amount of equipment and.... well, a lot of chemistry experience.
Journal of the American Chemical SocietyDOI: 10.1021/jacs.1c03141
Hongliang Chen, Feng Jiang, Chen Hu, Yang Jiao, Su Chen, Yunyan Qiu, Ping Zhou, Long Zhang, Kang Cai, Bo Song, Xiao-Yang Chen, Xingang Zhao, Michael R. Wasielewski, Hong Guo, Wenjing Hong, and J. Fraser Stoddart
https://ift.tt/3fRRyQi
Crystallinity is the key for the design of a new generation of carbon‐based catalysts for the oxidative dehydrogenation of ethanol to acetaldehyde. In their Research Article (DOI: 10.1002/anie.202014862), Bastian J. M. Etzold and co‐workers report the synthesis of a novel carbon catalyst that exhibits a comparatively large particle size (100 μm) while featuring an easily accessible crystalline nanostructure. An order of magnitude higher space‐time yields could be achieved with this new catalyst system compared to carbon nanotubes as benchmark.
https://ift.tt/2YFjSwZ
The direct dehydrogenation of alkanes is among the most efficient ways to access valuable alkene products. Although several catalysts have been designed to promote this transformation, they have unfortunately found limited applications in fine chemical synthesis. Here, we report a conceptually novel strategy for the catalytic, intermolecular dehydrogenation of alkanes using a ruthenium catalyst. The combination of a redox‐active ligand and a sterically hindered aryl radical intermediate has unleashed this novel strategy. Importantly, mechanistic investigations have been performed to provide a conceptual framework for the further development of this new catalytic dehydrogenation system.
https://ift.tt/39lVfe3
Journal of the American Chemical SocietyDOI: 10.1021/jacs.0c12415
Trevor N. Purdy, Min Cheol Kim, Reiko Cullum, William Fenical, and Bradley S. Moore
https://ift.tt/2Py70aT
Non‐oxidative dehydrogenation of propane to propylene plays an important role in light‐olefin chemical industry. However, the conversion and selectivity remain a fundamental challenge at low temperatures. Here we create and engineer high‐density Lewis acid sites at well‐defined surfaces in porous single‐crystalline Mo 2 N and MoN monoliths to enhance non‐oxidative dehydrogenation of propane to propylene. The top‐layer Mo ions with unsaturated Mo‐N 1/6 and Mo‐N 1/3 coordination structures create high‐density Lewis acid sites at surfaces, leading to the effective activation of C‐H bond without over cracking of C‐C bond during the non‐oxidative propane dehydrogenation. We demonstrate ~11% of propane conversion and ~95% of propylene selectivity with porous single‐crystalline Mo 2 N and MoN monoliths at 500 °C.
https://ift.tt/3cZIEAz
The products of methane dehydrogenation by gas‐phase Ta 4 + clusters are structurally characterized using infrared multiple photon dissociation (IRMPD) spectroscopy in conjunction with quantum chemical calculations. The obtained spectra of [4Ta,C,2H] + reveal a dominance of vibrational bands of a H 2 Ta 4 C + carbide dihydride structure over those of indicative for a HTa 4 CH + carbyne hydride one, as is unambiguously verified by studies employing various methane isotopologues. Because methane dehydrogenation by metal cations M + typically leads to the formation of either MCH 2 + carbene or HMCH + carbyne hydride structures, the observation of a H 2 MC + carbide dihydride structure implies that it is imperative to consider this often‐neglected class of carbonaceous intermediates in the reaction of metals with hydrocarbons.
https://ift.tt/3kKp1NE
An amine–borane system has been discovered to deliver a reversible dehydrogenation/regeneration at room temperature. It provides a new way for hydrogen storage under mild conditions.
Amine–borane complexes have been extensively studied as hydrogen storage materials. Herein, we report a new amine–borane system featuring a reversible dehydrogenation and regeneration at room temperature. In addition to high purity H2, the reaction between ethylenediamine bisborane (EDAB) and ethylenediamine (ED) leads to unique boron–carbon–nitrogen 5‐membered rings in the dehydrogenation product where one boron is tricoordinated by three nitrogen atoms. Owing to the unique cyclic structure, the dehydrogenation product can be efficiently converted back to EDAB by NaBH4 and H2O at room temperature. This finding could lead to the discovery of new amine boranes with potential usage as hydrogen storage materials.
https://ift.tt/2PRcYUZ
I've been doing some digging on the dehydrogenation of cyclohexane (and similar molecules with cyclohexane in it...) but haven't found much in the way of amateur synthesis. Has this route been considered? Rare metal catalysts (platinum, rhodium, iridium, rhenium, uranium) are needed for such a reaction. Are they simply not cost effective/obtainable for the average bee or has noone been ambitious enough to try?
In recent years, boron‐containing materials and in particular boron nitride, have been identified as highly selective catalysts for the oxidative dehydrogenation of alkanes such as propane. Until now, no mechanism exists that can explain both the unprecedented selectivity, the observed surface oxyfunctionalization, as well as the peculiar kinetic features of the reaction. In this contribution we combine catalytic activity measurements with quantum chemical calculations to put forward a bold new hypothesis. Based on our results, we argue that the remarkable product distribution can be rationalized by a combination of surface‐mediated formation of radicals over metastable sites, and their sequential propagation in the gas phase. Based on known radical propagation steps, we quantitatively describe the oxygen pressure‐dependent relative formation of the main product propylene and by‐product ethylene. The free radical intermediates are most likely what differentiates this catalytic system from less selective vanadium‐based catalysts. Indeed, although the mechanism of this benchmark catalyst is also not yet unambiguously established, it is generally assumed that radical intermediates are rapidly converted to stable molecular products on the catalyst surface before they can desorb. The new insights obtained in this work highlight the importance of the mechanistic differences between these two catalyst families which could lead to better design principles and improved catalytic systems.
https://ift.tt/2V8PWIw
Journal of the American Chemical SocietyDOI: 10.1021/jacs.0c10369
Wenbin Jiang, Jingxiang Low, Keke Mao, Delong Duan, Shuangming Chen, Wei Liu, Chih-Wen Pao, Jun Ma, Shuaikang Sang, Chang Shu, Xiaoyi Zhan, Zeming Qi, Hui Zhang, Zhi Liu, Xiaojun Wu, Ran Long, Li Song, and Yujie Xiong
https://ift.tt/3aTvgNq
An amorphous/graphitic hybrid material is synthesized by growing nanoscale graphite crystallites in a non‐nano polymer‐derived carbon by catalytic graphitization. An active dehydrogenation catalyst is obtained by creating accessibility to these graphitic domains via selective oxidation. This carbon dehydrogenation catalyst offers a 10‐fold increase in space‐time‐yield in the oxidative dehydrogenation of ethanol compared to a carbon nanotube benchmark.
A new strategy affords “non‐nano” carbon materials as dehydrogenation catalysts that perform similarly to nanocarbons. Polymer‐based carbon precursors that combine a soft‐template approach with ion adsorption and catalytic graphitization are key to this synthesis strategy, thus offering control over macroscopic shape, texture, and crystallinity and resulting in a hybrid amorphous/graphitic carbon after pyrolysis. From this intermediate the active carbon catalyst is prepared by removing the amorphous parts of the hybrid carbon materials via selective oxidation. The oxidative dehydrogenation of ethanol was chosen as test reaction, which shows that fine‐tuning the synthesis of the new carbon catalysts allows to obtain a catalytic material with an attractive high selectivity (82 %) similar to a carbon nanotube reference, while achieving 10 times higher space–time yields at 330 °C. This new class of carbon materials is accessible via a technically scalable, reproducible synthetic pathway and exhibits spherical particles with diameters around 100 μm, allowing unproblematic handling similar to classic non‐nano catalysts.
https://ift.tt/3sXExdN
Core‐shell nanocatalysts are particularly attractive due to their versatility and stability. Here, we describe cobalt nanoparticles encapsulated within graphitic shells prepared via the pyrolysis of a cationic polymer ionic liquid (PIL) with a cobalt(II) chloride anion. The resulting material has a core‐shell structure that displays excellent activity and selectivity in the self‐dehydrogenation and hetero‐dehydrogenation of primary amines to their corresponding imines. Furthermore, the catalyst exhibits excellent activity in the synthesis of secondary imines from substrates with various reducible functional groups (C=C, C≡C and C≡N) and amino acid derivatives.
https://ift.tt/2UMr367
Detection and characterization of fleeting reaction intermediates and active sites are crucial for molecular‐level knowledge of catalysis; insight that is required to understand the catalytic mechanisms, and to design novel high performance catalysts. We report a mass spectrometric study of the reactions of 3d early transition metal (vanadium, [Ar]3d 3 4s 2 ) cationic clusters with methanol in a low‐pressure collision cell. For comparison, the reaction of methanol with 3d late transition metal (cobalt, [Ar]3d 7 4s 2 ) cationic clusters were studied as well. In the vanadium case, the main reaction products are fully dehydrogenated species, and partial dehydrogenation and non‐dehydrogenation species are observed as minors, for which the relative intensities increase with cluster size and also at low cluster source temperature cooled by liquid nitrogen; while no dehydrogenation products have been observed for cobalt clusters. That demonstrates the strikingly different reactivity of vanadium and cobalt cationic clusters towards methanol. Quantum chemical calculations explored the reaction pathways and revealed that the fully dehydrogenation products of the reaction between V n + and methanol are V n (C)(O) + , in which C and O are separated due to the high oxophilicity of vanadium. The partial dehydrogenation and non‐dehydrogenation species observed in the experiment are verified to be reaction intermediates along the reaction pathway, and their most probable structures have been proposed.
https://ift.tt/2IHt2Vl
Chemical looping provides an energy and cost effective route for alkane utilization. However, there is considerable CO 2 co‐production caused by kinetically mismatched O 2‐ bulk diffusion in current chemical looping oxidative dehydrogenation systems, rendering a decreased olefin productivity. This paper describes the successful construction of sub‐monolayer or monolayer vanadia nanostructures to suppress CO 2 production in oxidative dehydrogenation of propane by evading the interference of O 2‐ bulk diffusion (monolayer versus multi‐layer). The highly dispersed vanadia nanostructures on titanium dioxide support showed over 90% propylene selectivity at 500 °C, exhibiting highest turnover frequency of 1.9×10 ‐2 s ‐1 , which is over 20 times greater than that of conventional crystalline V 2 O 5 oxygen carriers. Combining in situ spectroscopic characterizations and density functional theory calculation, we revealed the loading–reaction barrier relationship through the vanadia/titanium interfacial interaction. This work demonstrates that sub‐monolayer or monolayer nanostructures have the potential to serve as a general oxygen carrier materials platform for redox reactions.
https://ift.tt/2YyCYWa
A lean, mean, propylene machine: Subnanometer bimetallic Pt–Zn clusters are encapsulated inside silicalite‐1 (S‐1) zeolite via a ligand‐protected direct hydrogen reduction method. In the propane dehydrogenation (PDH) reaction, the PtZn4@S‐1‐H catalyst exhibited a very high propylene selectivity of 99.3 % and specific activity of propylene formation of 65.5 mol gPt−1 h−1 at 550 °C. Moreover, no obvious deactivation was observed over catalyst even after 13000 min on stream.
Propane dehydrogenation (PDH) has great potential to meet the increasing global demand for propylene, but the widely used Pt‐based catalysts usually suffer from short‐term stability and unsatisfactory propylene selectivity. Herein, we develop a ligand‐protected direct hydrogen reduction method for encapsulating subnanometer bimetallic Pt–Zn clusters inside silicalite‐1 (S‐1) zeolite. The introduction of Zn species significantly improved the stability of the Pt clusters and gave a superhigh propylene selectivity of 99.3 % with a weight hourly space velocity (WHSV) of 3.6–54 h−1 and specific activity of propylene formation of 65.5 mol gPt−1 h−1 (WHSV=108 h−1) at 550 °C. Moreover, no obvious deactivation was observed over PtZn4@S‐1‐H catalyst even after 13000 min on stream (WHSV=3.6 h−1), affording an extremely low deactivation constant of 0.001 h−1, which is 200 times lower than that of the PtZn4/Al2O3 counterpart under the same conditions. We also show that the introduction of Cs+ ions into the zeolite can improve the regeneration stability of catalysts, and the catalytic activity kept unchanged after four continuous cycles.
https://ift.tt/2Xkkc4Q
The small print : Co‐N‐C single‐atom catalysts were derived from metal– organic frameworks and compared with related nanoparticles in the selective dehydrogenation of formic acid. The highly dispersed single CoIIN x sites demonstrated improved reactivity and resistance to acid, constituting the current state‐of‐the‐art in low‐cost earth‐abundant catalyst for this transformation.
Metal–organic framework (MOF)‐derived Co‐N‐C catalysts with isolated single cobalt atoms have been synthesized and compared with cobalt nanoparticles for formic acid dehydrogenation. The atomically dispersed Co‐N‐C catalyst achieves superior activity, better acid resistance, and improved long‐term stability compared with nanoparticles synthesized by a similar route. High‐angle annular dark‐field–scanning transmission electron microscopy, X‐ray photoelectron spectroscopy, electron paramagnetic resonance, and X‐ray absorption fine structure characterizations reveal the formation of CoIINx centers as active sites. The optimal low‐cost catalyst is a promising candidate for liquid H2 generation.
https://ift.tt/2AiPSy1
Overcoming the mismatch between the rapid formation of nanoclusters and the slow crystallization of zeolites allows the in situ encapsulation of metal nanoclusters into zeolites in just a few minutes. The resultant Pt/Sn‐ZSM‐5 shows excellent activity and stability in the dehydrogenation propane to propylene.
Encapsulating metal nanoclusters into zeolites combines the superior catalytic activity of the nanoclusters with high stability and unique shape selectivity of the crystalline microporous materials. The preparation of such bifunctional catalysts, however, is often restricted by the mismatching in time scale between the fast formation of nanoclusters and the slow crystallization of zeolites. We herein demonstrate a novel strategy to overcome the mismatching issue, in which the crystallization of zeolites is expedited so as to synchronize it with the rapid formation of nanoclusters. The concept was demonstrated by confining Pt and Sn nanoclusters into a ZSM‐5 (MFI) zeolite in the course of its crystallization, leading to an ultrafast, in situ encapsulation within just 5 min. The Pt/Sn‐ZSM‐5 exhibited exceptional activity and selectivity with stability in the dehydrogenation of propane to propene. This method of ultrafast encapsulation opens up a new avenue for designing and synthesizing composite zeolitic materials with structural and compositional complexity.
https://ift.tt/2NX1Lh3
https://pubs.acs.org/doi/10.1021/acscatal.0c00556#
The requirement of caustic soda 20 wt% for those unit is seriously high. Something like 6 MT/hr. For what purpose will so much of NaOH be used. Also the Ethylene cracker and Propane unit then produce component feed for LDPE and PP units.
CO2‐mediated hydrogen storage energy cycle is a promising way to implement the hydrogen economy, but the exploration of efficient catalysts to achieve this process remains challenging. Herein, sub‐nanometer Pd‐Mn clusters were encaged within silicalite‐1 (S‐1) zeolites by a ligand‐protected method under direct hydrothermal conditions. The obtained zeolite‐encaged metallic nanocatalysts exhibited extraordinary catalytic activity and durability in both CO2 hydrogenation into formate and formic acid (FA) dehydrogenation back to CO2 and hydrogen. Thanks to the formation of ultrasmall metal clusters and the synergic effect of bi‐metallic components, the PdMn0.6@S‐1 catalyst afforded a formate generation rate of 2151 molformate molPd‐1 h‐1 at 353 K, and an initial turnover frequency of 6860 molH2 molPd‐1 h‐1 for CO‐free FA decomposition at 333 K without any additive. Both values represent the top levels among the state‐of‐the‐art heterogeneous catalysts under similar conditions. This work demonstrates that zeolite‐encaged metallic catalysts hold great promise to realize CO2‐mediated hydrogen energy cycles in the future featuring fast charging and releasing kinetics.
https://ift.tt/3aiSSc1
Journal of the American Chemical SocietyDOI: 10.1021/jacs.0c07792
https://ift.tt/3mbGsrK
I'm working with some dehydrogenation catalysts which are essentially supported Pd on Cu. I've finished up some work on another reaction, so now I've moved on to this and started looking for protocols. All of them that I've seen so far for, say, propane dehydrogenation are for example, 5:20:75 Propane:Hydrogen:Helium or something including the corresponding alkene like 5:20:75 Propane:Hydrogen:Propene, and I was wondering about the purpose of the hydrogen and propene.
I can say that without them, conversions are much lower than expected, basically none detectable. I'm assuming that these are both used to suppress side reactions and keep conversions low. Propene primarily to keep the conversion down since this is an equilibrium? And for hydrogen I'm assuming this is to help prevent deep dehydrogenation and coking? It seems like high H2 concentrations will ensure a significant amount of H remains adsorbed to the Pd domains to reduce the catalytically active ensemble size to avoid these problems.
Any insight is appreciated!
Although hexagonal boron nitride (h‐BN) has recently been identified as a highly efficient catalyst for the oxidative dehydrogenation of propane (ODHP) reaction, the reaction mechanisms, especially regarding radical chemistry of this system, remain elusive. Herein we report the first direct experimental evidence of gas‐phase methyl radicals (CH 3 ∙) in the ODHP reaction over boron‐based catalysts by using an online synchrotron vacuum ultraviolet photoionization mass spectroscopy (SVUV‐PIMS), which uncovers the existence of gas‐phase radical pathways. Combined with density functional theory (DFT) calculations, our results demonstrate that propene is mainly generated on the catalyst surface from the C‐H activation of propane while C 2 and C 1 products can be formed via both surface‐mediated and gas‐phase pathways. These observations provide new insights towards understanding the ODHP reaction mechanisms over boron‐based catalysts.
https://ift.tt/2xW7LSb
Journal of the American Chemical SocietyDOI: 10.1021/jacs.9b13865
https://ift.tt/2Tg4TaY
Does anyone have an opinion about whether the "Dehydrogenation of 1,4-Butanediol (1,4-BD) to gamma-Butyrolactone (GBL)" is a better option than "Solvent free permanganate oxidations using (1,4-BD) to GBL" which sythesis requires the least amount of equipment and.... well, a lot of chemistry experience.
An approach to the catalytic dehydrogenation of alkanes and heterocycles uses Ru and redox‐active ligands. A wide range of functionalized substrates afforded dehydrogenated products in good yields. Preliminary mechanistic studies suggest that a redox‐active ligand‐assisted intermolecular hydrogen atom transfer is crucial to this process.
The direct dehydrogenation of alkanes is among the most efficient ways to access valuable alkene products. Although several catalysts have been designed to promote this transformation, they have unfortunately found limited applications in fine chemical synthesis. Here, we report a conceptually novel strategy for the catalytic, intermolecular dehydrogenation of alkanes using a ruthenium catalyst. The combination of a redox‐active ligand and a sterically hindered aryl radical intermediate has unleashed this novel strategy. Importantly, mechanistic investigations have been performed to provide a conceptual framework for the further development of this new catalytic dehydrogenation system.
https://ift.tt/3ln0pMa
An approach to the catalytic dehydrogenation of alkanes and heterocycles uses Ru and redox‐active ligands. A wide range of functionalized substrates afforded dehydrogenated products in good yields. Preliminary mechanistic studies suggest that a redox‐active ligand‐assisted intermolecular hydrogen atom transfer is crucial to this process.
The direct dehydrogenation of alkanes is among the most efficient ways to access valuable alkene products. Although several catalysts have been designed to promote this transformation, they have unfortunately found limited applications in fine chemical synthesis. Here, we report a conceptually novel strategy for the catalytic, intermolecular dehydrogenation of alkanes using a ruthenium catalyst. The combination of a redox‐active ligand and a sterically hindered aryl radical intermediate has unleashed this novel strategy. Importantly, mechanistic investigations have been performed to provide a conceptual framework for the further development of this new catalytic dehydrogenation system.
https://ift.tt/39lVfe3
Strikingly different reactivity of vanadium and cobalt cationic clusters towards methanol in a low‐pressure collision cell is observed by mass spectrometry. Metastable or kinetically trapped reaction intermediates of the methanol reaction with vanadium cationic clusters are verified, and their structures are proposed by exploring the reaction pathways using density functional theory calculations.
A mass spectrometric study of the reactions of vanadium cationic clusters with methanol in a low‐pressure collision cell is reported. For comparison, the reaction of methanol with cobalt cationic clusters was studied. For vanadium, the main reaction products are fully dehydrogenated species, and partial dehydrogenation and non‐dehydrogenation species are observed as minors, for which the relative intensities increase with cluster size and also at low cluster source temperature cooled by liquid nitrogen; no dehydrogenation products were observed for cobalt clusters. Quantum chemical calculations explored the reaction pathways and revealed that the fully dehydrogenation products of the reaction between V n+ and methanol are V n (C)(O)+, in which C and O are separated owing to the high oxophilicity of vanadium. The partial dehydrogenation and non‐dehydrogenation species were verified to be reaction intermediates along the reaction pathway, and their most probable structures were proposed.
https://ift.tt/2IHt2Vl
Tantalum carbide dihydride cations are identified as products in the reaction of methane with gas‐phase Ta4+ clusters by IR spectroscopy, in conjunction with density‐functional theory calculations.
The products of methane dehydrogenation by gas‐phase Ta4+ clusters are structurally characterized using infrared multiple photon dissociation (IRMPD) spectroscopy in conjunction with quantum chemical calculations. The obtained spectra of [4Ta,C,2H]+ reveal a dominance of vibrational bands of a H2Ta4C+ carbide dihydride structure over those indicative for a HTa4CH+ carbyne hydride one, as is unambiguously verified by studies employing various methane isotopologues. Because methane dehydrogenation by metal cations M+ typically leads to the formation of either MCH2+ carbene or HMCH+ carbyne hydride structures, the observation of a H2MC+ carbide dihydride structure implies that it is imperative to consider this often‐neglected class of carbonaceous intermediates in the reaction of metals with hydrocarbons.
https://ift.tt/3kKp1NE
The loading–reaction‐barrier relationship over VO x /TiO2 catalysts is investigated for chemical looping oxidative dehydrogenation of propane. Sub‐monolayer or monolayer vanadia nanostructures, compared with conventional crystalline V2O5 oxygen carriers, dramatically suppress the CO2 co‐production by evading O2− bulk diffusion and subsequent evolution into surface electrophilic oxygen species.
Chemical looping provides an energy‐ and cost‐effective route for alkane utilization. However, there is considerable CO2 co‐production caused by kinetically mismatched O2− bulk diffusion and surface reaction in current chemical looping oxidative dehydrogenation systems, rendering a decreased olefin productivity. Sub‐monolayer or monolayer vanadia nanostructures are successfully constructed to suppress CO2 production in oxidative dehydrogenation of propane by evading the interference of O2− bulk diffusion (monolayer versus multi‐layers). The highly dispersed vanadia nanostructures on titanium dioxide support showed over 90 % propylene selectivity at 500 °C, exhibiting turnover frequency of 1.9×10−2 s−1, which is over 20 times greater than that of conventional crystalline V2O5. Combining in situ spectroscopic characterizations and DFT calculations, we reveal the loading–reaction barrier relationship through the vanadia/titanium interfacial interaction.
https://ift.tt/2YyCYWa
The loading–reaction‐barrier relationship over VO x /TiO2 catalysts is investigated for chemical looping oxidative dehydrogenation of propane. Sub‐monolayer or monolayer vanadia nanostructures, compared with conventional crystalline V2O5 oxygen carriers, dramatically suppress the CO2 co‐production by evading O2− bulk diffusion and subsequent evolution into surface electrophilic oxygen species.
Chemical looping provides an energy‐ and cost‐effective route for alkane utilization. However, there is considerable CO2 co‐production caused by kinetically mismatched O2− bulk diffusion and surface reaction in current chemical looping oxidative dehydrogenation systems, rendering a decreased olefin productivity. Sub‐monolayer or monolayer vanadia nanostructures are successfully constructed to suppress CO2 production in oxidative dehydrogenation of propane by evading the interference of O2− bulk diffusion (monolayer versus multi‐layers). The highly dispersed vanadia nanostructures on titanium dioxide support showed over 90 % propylene selectivity at 500 °C, exhibiting turnover frequency of 1.9×10−2 s−1, which is over 20 times greater than that of conventional crystalline V2O5. Combining in situ spectroscopic characterizations and DFT calculations, we reveal the loading–reaction barrier relationship through the vanadia/titanium interfacial interaction.
https://ift.tt/2YyCYWa
High propylene selectivity during oxidative dehydrogenation catalyzed by hexagonal boron nitride originates from surface‐initiated radical reactions that propagate via gas‐phase chemistry. This reaction network contrasts with previously studied vanadium‐based catalysts where surface reactions predominate and lower selectivity. An experimental and computational approach was used to probe this complex surface–gas‐phase reaction network.
Boron‐containing materials, and in particular boron nitride, have recently been identified as highly selective catalysts for the oxidative dehydrogenation of alkanes such as propane. To date, no mechanism exists that can explain both the unprecedented selectivity, the observed surface oxyfunctionalization, and the peculiar kinetic features of this reaction. We combine catalytic activity measurements with quantum chemical calculations to put forward a bold new hypothesis. We argue that the remarkable product distribution can be rationalized by a combination of surface‐mediated formation of radicals over metastable sites, and their sequential propagation in the gas phase. Based on known radical propagation steps, we quantitatively describe the oxygen pressure‐dependent relative formation of the main product propylene and by‐product ethylene. Free radical intermediates most likely differentiate this catalytic system from less selective vanadium‐based catalysts.
https://ift.tt/2V8PWIw
MOF‐derived Co‐N‐C catalysts with isolated single cobalt atoms have been synthesized and compared with cobalt nanoparticles for formic acid dehydrogenation. The atomically dispersed Co‐N‐C catalyst achieves superior activity, better acid resistance and improved long‐term stability compared with nanoparticles synthesized by a similar route. HAADF‐STEM, XPS, EPR and XAFS characterizations reveal the formation of Co(II)Nx centers as active sites. The optimal low‐cost catalyst is a promising candidate for liquid H2 generation.
https://ift.tt/2AiPSy1
Journal of the American Chemical SocietyDOI: 10.1021/jacs.9b12706
https://ift.tt/2tiDCdY
High propylene selectivity during oxidative dehydrogenation catalyzed by hexagonal boron nitride originates from surface‐initiated radical reactions that propagate via gas‐phase chemistry. This reaction network contrasts with previously studied vanadium‐based catalysts where surface reactions predominate and lower selectivity. An experimental and computational approach was used to probe this complex surface–gas‐phase reaction network.
Boron‐containing materials, and in particular boron nitride, have recently been identified as highly selective catalysts for the oxidative dehydrogenation of alkanes such as propane. To date, no mechanism exists that can explain both the unprecedented selectivity, the observed surface oxyfunctionalization, and the peculiar kinetic features of this reaction. We combine catalytic activity measurements with quantum chemical calculations to put forward a bold new hypothesis. We argue that the remarkable product distribution can be rationalized by a combination of surface‐mediated formation of radicals over metastable sites, and their sequential propagation in the gas phase. Based on known radical propagation steps, we quantitatively describe the oxygen pressure‐dependent relative formation of the main product propylene and by‐product ethylene. Free radical intermediates most likely differentiate this catalytic system from less selective vanadium‐based catalysts.
https://ift.tt/2V8PWIw
The self‐dehydrogenation and hetero‐dehydrogenation of primary amines to their corresponding imines was achieved employing carbon supported cobalt nanoparticles coated with nitrogen‐doped graphene shell. The catalyst is obtained via pyrolysis of a polymer ionic liquid with a CoCl42− counter‐anion on a carbon support and shows unprecedented activity in these reactions.
Core–shell nanocatalysts are attractive due to their versatility and stability. Here, we describe cobalt nanoparticles encapsulated within graphitic shells prepared via the pyrolysis of a cationic poly‐ionic liquid (PIL) with a cobalt(II) chloride anion. The resulting material has a core–shell structure that displays excellent activity and selectivity in the self‐dehydrogenation and hetero‐dehydrogenation of primary amines to their corresponding imines. Furthermore, the catalyst exhibits excellent activity in the synthesis of secondary imines from substrates with various reducible functional groups (C=C, C≡C and C≡N) and amino acid derivatives.
https://ift.tt/2UMr367
Propane dehydrogenation (PDH) has great potential to meet the increasing global demand for propylene, but the widely‐used Pt‐based catalysts usually suffer from short‐term stability and unsatisfactory propylene selectivity. Here, we developed a ligand‐protected direct hydrogen reduction method for encapsulating subnanometer bimetallic Pt‐Zn clusters inside silicalite‐1 (S‐1) zeolite. The introduction of Zn species significantly improved the stability of the Pt clusters and exhibited a superhigh propylene selectivity of 99.3% with a weight hourly space velocity (WHSV) of 3.6~54 h ‐1 and specific activity of propylene formation of 65.5 mol C3H6 g Pt ‐1 h ‐1 (WHSV=108 h ‐1 ) at 550 °C. Moreover, no obvious deactivation was observed over PtZn4@S‐1‐H catalyst even after 13000 min on stream (WHSV=3.6 h ‐1 ), affording an extremely low deactivation constant of 0.001 h ‐1 , which is 200 times lower than that of the PtZn4/Al 2 O 3 counterpart under the same conditions. Significantly, the introduction of Cs + ions into the zeolite can improve the regeneration stability of catalysts, and the catalytic activity kept unchanged after four continuous cycles. These zeolite‐encaged Pt‐Zn catalysts represent the best performance s to date for PDH conversions, promising their practical industrial applications.
https://ift.tt/2Xkkc4Q
The self‐dehydrogenation and hetero‐dehydrogenation of primary amines to their corresponding imines was achieved employing carbon supported cobalt nanoparticles coated with nitrogen‐doped graphene shell. The catalyst is obtained via pyrolysis of a polymer ionic liquid with a CoCl42− counter‐anion on a carbon support and shows unprecedented activity in these reactions.
Core–shell nanocatalysts are attractive due to their versatility and stability. Here, we describe cobalt nanoparticles encapsulated within graphitic shells prepared via the pyrolysis of a cationic poly‐ionic liquid (PIL) with a cobalt(II) chloride anion. The resulting material has a core–shell structure that displays excellent activity and selectivity in the self‐dehydrogenation and hetero‐dehydrogenation of primary amines to their corresponding imines. Furthermore, the catalyst exhibits excellent activity in the synthesis of secondary imines from substrates with various reducible functional groups (C=C, C≡C and C≡N) and amino acid derivatives.
https://ift.tt/2UMr367
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