scholarly journals Outstanding Performance of Highly-Dispersed Zinc Species on Zeolites for the Continuous and Selective Dehydrogenation of Ethane with CO2 as Soft Oxidant

2020 ◽  
Author(s):  
Jiaxu Liu ◽  
Ning He ◽  
Zhenmei Zhang ◽  
Jinpeng Yang ◽  
Xiao Jiang ◽  
...  
Keyword(s):  
Heterogeneous Catalysts ◽  
Catalytic Performance ◽  
Ethane Conversion ◽  
Platform Chemicals ◽  
Rate Limiting Step ◽  
Zeolite Support ◽  
Highly Dispersed ◽  
Byproduct Formation ◽  
Soft Oxidant ◽  
Rate Limiting

<div> <div> <div> <p>We report herein the preparation, characterization, and outstanding catalytic performance of a series of heterogeneous catalysts featuring highly-dispersed zinc sites on zeolitic SSZ-13 and ZSM-5 frameworks. The materials were evaluated in the oxidative dehydrogenation of ethane with CO2 as a soft oxidant, a very important reaction for the synthesis of platform chemicals. In particular, we found that Zn2.92/NaS50 exhibits high ethane conversion ability, excellent CO2 transformation ability, and good selectivity. In line with the experimental results, we show that the highly-selective character is due to the characteristic compositional structure of the zeolite support and its topology that can effectively confine CO2. An in-depth molecular analysis via operando studies and DFT calculation showed that the rate-limiting step of reaction with CO2 was the second C-H bond dissociation to give ethene. The addition of CO2 effectively reduced the energy barrier of this step, favoring desorption and limiting byproduct formation. Overall, this work demonstrates the breakthrough potential of novel heterogeneous catalysts made of highly-dispersed zinc species on zeolites in relevant transformations. </p> </div> </div> </div>

scholarly journals Outstanding Performance of Highly-Dispersed Zinc Species on Zeolites for the Continuous and Selective Dehydrogenation of Ethane with CO2 as Soft Oxidant

2020 ◽  
Author(s):  
Jiaxu Liu ◽  
Ning He ◽  
Zhenmei Zhang ◽  
Jinpeng Yang ◽  
Xiao Jiang ◽  
...  
Keyword(s):  
Heterogeneous Catalysts ◽  
Catalytic Performance ◽  
Ethane Conversion ◽  
Platform Chemicals ◽  
Rate Limiting Step ◽  
Zeolite Support ◽  
Highly Dispersed ◽  
Byproduct Formation ◽  
Soft Oxidant ◽  
Rate Limiting

<div> <div> <div> <p>We report herein the preparation, characterization, and outstanding catalytic performance of a series of heterogeneous catalysts featuring highly-dispersed zinc sites on zeolitic SSZ-13 and ZSM-5 frameworks. The materials were evaluated in the oxidative dehydrogenation of ethane with CO2 as a soft oxidant, a very important reaction for the synthesis of platform chemicals. In particular, we found that Zn2.92/NaS50 exhibits high ethane conversion ability, excellent CO2 transformation ability, and good selectivity. In line with the experimental results, we show that the highly-selective character is due to the characteristic compositional structure of the zeolite support and its topology that can effectively confine CO2. An in-depth molecular analysis via operando studies and DFT calculation showed that the rate-limiting step of reaction with CO2 was the second C-H bond dissociation to give ethene. The addition of CO2 effectively reduced the energy barrier of this step, favoring desorption and limiting byproduct formation. Overall, this work demonstrates the breakthrough potential of novel heterogeneous catalysts made of highly-dispersed zinc species on zeolites in relevant transformations. </p> </div> </div> </div>

scholarly journals Single Molecular Catalysis Identifying Activation Energy of Intermediate Product and Rate-Limiting Step in Plasmonic Photocatalysis

2019 ◽  
Author(s):  
Di Li
Keyword(s):  
Activation Energy ◽  
High Performance ◽  
Variable Temperature ◽  
Chemical Conversion ◽  
Catalytic Performance ◽  
Localized Surface Plasmon ◽  
Spatiotemporal Resolution ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

Plasmon mediated photocatalysis provides a novel strategy for harvesting solar energy. Identification of rate determining step and its activation energy in plasmon mediated photocatalysis plays critical roles for understanding the contribution of hot carriers that facilitates rational designing catalysts with integrated high photo-chemical conversion efficiency and catalytic performance. However, it remains a challenge due to a lack of research tools with spatiotemporal resolution that capable of capturing intermediates. In this work, we used a single molecular fluorescence approach to investigate a localized surface plasmon resonance (LSPR) enhanced photocatalytic reaction with sub-turnover resolution. By introducing variable temperature as an independent parameter in plasmonic photocatalysis, the activation energies of tandem reaction steps, including intermediate generation, product generation and product dissociation, were clearly differentiated, and intermediates generation was found to be the rate-limiting step. Remarkably, the cause of plasmon enhanced catalysis performance was found to be its ability of lowering the activation energy of intermediates generation. This study gives new insight into the photo-chemical energy conversion pathways in plasmon enhanced photocatalysis and sheds light on designing high performance plasmonic catalysts.

scholarly journals Single Molecular Catalysis Identifying Activation Energy of Intermediate Product and Rate-Limiting Step in Plasmonic Photocatalysis

2019 ◽  
Author(s):  
Di Li
Keyword(s):  
Activation Energy ◽  
High Performance ◽  
Variable Temperature ◽  
Chemical Conversion ◽  
Catalytic Performance ◽  
Localized Surface Plasmon ◽  
Spatiotemporal Resolution ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

Plasmon mediated photocatalysis provides a novel strategy for harvesting solar energy. Identification of rate determining step and its activation energy in plasmon mediated photocatalysis plays critical roles for understanding the contribution of hot carriers that facilitates rational designing catalysts with integrated high photo-chemical conversion efficiency and catalytic performance. However, it remains a challenge due to a lack of research tools with spatiotemporal resolution that capable of capturing intermediates. In this work, we used a single molecular fluorescence approach to investigate a localized surface plasmon resonance (LSPR) enhanced photocatalytic reaction with sub-turnover resolution. By introducing variable temperature as an independent parameter in plasmonic photocatalysis, the activation energies of tandem reaction steps, including intermediate generation, product generation and product dissociation, were clearly differentiated, and intermediates generation was found to be the rate-limiting step. Remarkably, the cause of plasmon enhanced catalysis performance was found to be its ability of lowering the activation energy of intermediates generation. This study gives new insight into the photo-chemical energy conversion pathways in plasmon enhanced photocatalysis and sheds light on designing high performance plasmonic catalysts.

scholarly journals Exploiting two-dimensional morphology of molybdenum oxycarbide to enable efficient catalytic dry reforming of methane

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Alexey Kurlov ◽  
Evgeniya B. Deeva ◽  
Paula M. Abdala ◽  
Dmitry Lebedev ◽  
Athanasia Tsoukalou ◽  
...  
Keyword(s):  
Contact Time ◽  
Specific Activity ◽  
Catalytic Performance ◽  
Dry Reforming ◽  
Dry Reforming Of Methane ◽  
Two Dimensional ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Oxygen Coverage ◽  
Rate Limiting

Abstract The two-dimensional morphology of molybdenum oxycarbide (2D-Mo2COx) nanosheets dispersed on silica is found vital for imparting high stability and catalytic activity in the dry reforming of methane. Here we report that owing to the maximized metal utilization, the specific activity of 2D-Mo2COx/SiO2 exceeds that of other Mo2C catalysts by ca. 3 orders of magnitude. 2D-Mo2COx is activated by CO2, yielding a surface oxygen coverage that is optimal for its catalytic performance and a Mo oxidation state of ca. +4. According to ab initio calculations, the DRM proceeds on Mo sites of the oxycarbide nanosheet with an oxygen coverage of 0.67 monolayer. Methane activation is the rate-limiting step, while the activation of CO2 and the C–O coupling to form CO are low energy steps. The deactivation of 2D-Mo2COx/SiO2 under DRM conditions can be avoided by tuning the contact time, thereby preventing unfavourable oxygen surface coverages.

Ornithine Decarboxylase Activity in Cultured Endothelial Cells Stimulated by Serum, Thrombin and Serotonin

1978 ◽  
Vol 39 (02) ◽  
pp. 496-503 ◽  
Author(s):  
P A D’Amore ◽  
H B Hechtman ◽  
D Shepro
Keyword(s):  
Endothelial Cells ◽  
Ornithine Decarboxylase ◽  
Decarboxylase Activity ◽  
Aortic Endothelial Cells ◽  
Ornithine Decarboxylase Activity ◽  
Rate Limiting Step ◽  
Bovine Aortic Endothelial Cells ◽  
Limiting Step ◽  
Rate Limiting ◽  
Serum Serotonin

SummaryOrnithine decarboxylase (ODC) activity, the rate-limiting step in the synthesis of polyamines, can be demonstrated in cultured, bovine, aortic endothelial cells (EC). Serum, serotonin and thrombin produce a rise in ODC activity. The serotonin-induced ODC activity is significantly blocked by imipramine (10-5 M) or Lilly 11 0140 (10-6M). Preincubation of EC with these blockers together almost completely depresses the 5-HT-stimulated ODC activity. These observations suggest a manner by which platelets may maintain EC structural and metabolic soundness.

Dynamics of hepatic and peripheral insulin effects suggest common rate-limiting step in vivo

Diabetes ◽  
1993 ◽  
Vol 42 (2) ◽  
pp. 296-306 ◽  
Author(s):  
D. C. Bradley ◽  
R. A. Poulin ◽  
R. N. Bergman
Keyword(s):  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

Cobalt/Lewis Acid Catalysis for Hydrocarbofunctionalization of Alkynes via Cooperative C–H Activation

2020 ◽  
Author(s):  
Chang-Sheng Wang ◽  
Sabrina Monaco ◽  
Anh Ngoc Thai ◽  
Md. Shafiqur Rahman ◽  
Chen Wang ◽  
...  
Keyword(s):  
Catalytic System ◽  
Lewis Acid ◽  
Hydrogen Transfer ◽  
Acid Catalysis ◽  
Rate Limiting Step ◽  
Site Selectivity ◽  
Set Up ◽  
Site Selective ◽  
First Time ◽  
Rate Limiting

A catalytic system comprised of a cobalt-diphosphine complex and a Lewis acid (LA) such as AlMe3 has been found to promote hydrocarbofunctionalization reactions of alkynes with Lewis basic and electron-deficient substrates such as formamides, pyridones, pyridines, and azole derivatives through site-selective C-H activation. Compared with known Ni/LA catalytic system for analogous transformations, the present catalytic system not only feature convenient set up using inexpensive and bench-stable precatalyst and ligand such as Co(acac)3 and 1,3-bis(diphenylphosphino)propane (dppp), but also display distinct site-selectivity toward C-H activation of pyridone and pyridine derivatives. In particular, a completely C4-selective alkenylation of pyridine has been achieved for the first time. Mechanistic stidies including DFT calculations on the Co/Al-catalyzed addition of formamide to alkyne have suggested that the reaction involves cleavage of the carbamoyl C-H bond as the rate-limiting step, which proceeds through a ligand-to-ligand hydrogen transfer (LLHT) mechanism leading to an alkyl(carbamoyl)cobalt intermediate.

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