Catalyst Activation and Kinetics for Propylene Metathesis by Supported WOx/SiO2 Catalysts

ACS Catalysis ◽  
2016 ◽  
Vol 7 (1) ◽  
pp. 573-580 ◽  
Author(s):  
Soe Lwin ◽  
Israel E. Wachs
Keyword(s):  
Catalyst Activation ◽  
Propylene Metathesis

Mechanistic Insights into Fe Catalyzed α-C-H Oxidations of Tertiary Amines

2019 ◽  
Author(s):  
Christopher J. Legacy ◽  
Frederick T. Greenaway ◽  
Marion Emmert
Keyword(s):  
Free Radical ◽  
Catalytic Mechanism ◽  
Catalyst System ◽  
Oxidation Products ◽  
Tertiary Amines ◽  
Catalyst Activation ◽  
Rate Determining Step ◽  
Fe Catalyst ◽  
Ligand Coordination ◽  
Rate Kinetics

We report detailed mechanistic investigations of an iron-based catalyst system, which allows the α-C-H oxidation of a wide variety of amines, including acyclic tertiary aliphatic amines, to afford dealkylated or amide products. In contrast to other catalysts that affect α-C-H oxidations of tertiary amines, the system under investigation employs exclusively peroxy esters as oxidants. More common oxidants (e.g. tBuOOH) previously reported to affect amine oxidations via free radical pathways do not provide amine α-C-H oxidation products in combination with the herein described catalyst system. Motivated by this difference in reactivity to more common free radical systems, the investigations described herein employ initial rate kinetics, kinetic profiling, Eyring studies, kinetic isotope effect studies, Hammett studies, ligand coordination studies, and EPR studies to shed light on the Fe catalyst system. The obtained data suggest that the catalytic mechanism proceeds through C-H abstraction at a coordinated substrate molecule. This rate-determining step occurs either at an Fe(IV) oxo pathway or a 2-electron pathway at a Fe(II) intermediate with bound oxidant. We further show via kinetic profiling and EPR studies that catalyst activation follows a radical pathway, which is initiated by hydrolysis of PhCO3 tBu to tBuOOH in the reaction mixture. Overall, the obtained mechanistic data support a non-classical, Fe catalyzed pathway that requires substrate binding, thus inducing selectivity for α-C-H functionalization.<br>

scholarly journals Low Temperature Water-Gas Shift: Enhancing Stability through Optimizing Rb Loading on Pt/ZrO2

Catalysts ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 210
Author(s):  
Caleb Daniel Watson ◽  
Michela Martinelli ◽  
Donald Charles Cronauer ◽  
A. Jeremy Kropf ◽  
Gary Jacobs
Keyword(s):  
Low Temperature ◽  
Hydrogen Transfer ◽  
Water Gas Shift ◽  
Significant Shift ◽  
Catalyst Activation ◽  
X Ray ◽  
Temperature Programmed ◽  
Water Gas ◽  
X Ray Absorption ◽  
Temperature Water

Recent studies have shown that appropriate levels of alkali promotion can significantly improve the rate of low-temperature water gas shift (LT-WGS) on a range of catalysts. At sufficient loadings, the alkali metal can weaken the formate C–H bond and promote formate dehydrogenation, which is the proposed rate determining step in the formate associative mechanism. In a continuation of these studies, the effect of Rb promotion on Pt/ZrO2 is examined herein. Pt/ZrO2 catalysts were prepared with several different Rb loadings and characterized using temperature programmed reduction mass spectrometry (TPR-MS), temperature programmed desorption (TPD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), an X-ray absorption near edge spectroscopy (XANES) difference procedure, extended X-ray absorption fine structure spectroscopy (EXAFS) fitting, TPR-EXAFS/XANES, and reactor testing. At loadings of 2.79% Rb or higher, a significant shift was seen in the formate ν(CH) band. The results showed that a Rb loading of 4.65%, significantly improves the rate of formate decomposition in the presence of steam via weakening the formate C–H bond. However, excessive rubidium loading led to the increase in stability of a second intermediate, carbonate and inhibited hydrogen transfer reactions on Pt through surface blocking and accelerated agglomeration during catalyst activation. Optimal catalytic performance was achieved with loadings in the range of 0.55–0.93% Rb, where the catalyst maintained high activity and exhibited higher stability in comparison with the unpromoted catalyst.

scholarly journals Towards High Efficacy of Pd-Au/C Catalyst for Tetrachloromethane Hydrodechlorination

Chemistry ◽  
2021 ◽  
Vol 3 (1) ◽  
pp. 338-359
Author(s):  
Magdalena Bonarowska ◽  
Zbigniew Kaszkur ◽  
Krzysztof Matus ◽  
Alicja Drelinkiewicz ◽  
Tomasz Szumełda ◽  
...  
Keyword(s):  
Microwave Irradiation ◽  
Gas Phase ◽  
Thermal Activation ◽  
Supported Catalysts ◽  
Carbon Support ◽  
Thermal Reduction ◽  
Microwave Oven ◽  
Optimal Conditions ◽  
Catalyst Activation ◽  
Critical Part

We present an efficient strategy for synthesising the PdAu catalysts with a homogeneous PdAu alloy phase for environmentally important hydrodechlorination of tetrachloromethane in the gas phase. The synthesis of carbon-supported catalysts involved two major steps: (i) incorporation of palladium and gold nanoparticles into carbon support and (ii) activation of the catalysts. The critical part of this work was to find the optimal conditions for both steps. Thus, the incorporation of the nanoparticles was carried out in two ways, by impregnation and direct redox reaction method using acetone solutions of metal precursor salts. The activation was performed either by a conventional thermal reduction in hydrogen or flash irradiation in a microwave oven. The homogeneity and structure of the PdAu alloy were found to depend on the catalyst activation method critically. In all cases, we observed better homogeneity for catalysts that were subject to microwave irradiation. Moreover, the flash microwave irradiation of prepared catalysts provided catalysts of better stability and selectivity towards the desired products (hydrocarbons) in the hydrodechlorination of tetrachloromethane as compared to the catalyst obtained by conventional thermal activation in hydrogen.

scholarly journals Robust and efficient hydrogenation of carbonyl compounds catalysed by mixed donor Mn(I) pincer complexes

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Wenjun Yang ◽  
Ivan Yu. Chernyshov ◽  
Robin K. A. van Schendel ◽  
Manuela Weber ◽  
Christian Müller ◽  
...  
Keyword(s):  
Noble Metal ◽  
Crucial Role ◽  
Carbonyl Compounds ◽  
Catalytic Performance ◽  
Hydrogen Atmosphere ◽  
Pincer Complexes ◽  
Catalyst Activation ◽  
Hydrogenation Catalysts ◽  
Induction Times

AbstractAny catalyst should be efficient and stable to be implemented in practice. This requirement is particularly valid for manganese hydrogenation catalysts. While representing a more sustainable alternative to conventional noble metal-based systems, manganese hydrogenation catalysts are prone to degrade under catalytic conditions once operation temperatures are high. Herein, we report a highly efficient Mn(I)-CNP pre-catalyst which gives rise to the excellent productivity (TOF° up to 41 000 h−1) and stability (TON up to 200 000) in hydrogenation catalysis. This system enables near-quantitative hydrogenation of ketones, imines, aldehydes and formate esters at the catalyst loadings as low as 5–200 p.p.m. Our analysis points to the crucial role of the catalyst activation step for the catalytic performance and stability of the system. While conventional activation employing alkoxide bases can ultimately provide catalytically competent species under hydrogen atmosphere, activation of Mn(I) pre-catalyst with hydride donor promoters, e.g. KHBEt3, dramatically improves catalytic performance of the system and eliminates induction times associated with slow catalyst activation.

scholarly journals Identifying the Catalytic Active Site for Propylene Metathesis by Supported ReOx Catalysts

ACS Catalysis ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 1962-1976
Author(s):  
Bin Zhang ◽  
Israel E. Wachs
Keyword(s):  
Active Site ◽  
Catalytic Active Site ◽  
Propylene Metathesis

scholarly journals Steam reforming of ethanol for hydrogen production: influence of catalyst composition (Ni/Al2O3, Ni/Al2O3–CeO2, Ni/Al2O3–ZnO) and process conditions

2021 ◽  
Vol 132 (2) ◽  
pp. 907-919
Author(s):  
O. Shtyka ◽  
Z. Dimitrova ◽  
R. Ciesielski ◽  
A. Kedziora ◽  
G. Mitukiewicz ◽  
...  
Keyword(s):  
Hydrogen Production ◽  
Steam Reforming ◽  
Catalyst Stability ◽  
Feed Ratio ◽  
Ethanol Conversion ◽  
Process Conditions ◽  
Catalyst Activation ◽  
Catalyst Composition ◽  
Activity Measurements ◽  
Steam Reforming Of Ethanol

AbstractEthanol steam reforming was studied over Ni supported catalysts. The effects of support (Al2O3, Al2O3–ZnO, and Al2O3–CeO2), metal loading, catalyst activation method, and steam-to-ethanol molar feed ratio were investigated. The properties of catalysts were studied by N2 physisorption, TPD-CO2, X-ray diffraction, and temperature programmed reduction. After activity tests, the catalysts were analyzed by TOC analysis. The catalytic activity measurements showed that the addition either of ZnO SSor CeO2 to alumina enhances both ethanol conversion and promotes selectivity towards hydrogen formation. The same effects were observed for catalysts with higher metal loadings. High process temperature and high water-to-ethanol ratio were found to be beneficial for hydrogen production. An extended catalyst stability tests showed no loss of activity over 50 h on reaction stream. The TOC analysis of spent catalysts revealed only insignificant amounts of carbon deposit.

Propylene Metathesis by Use of Novel TiCl4or Ti(O-i-Pr)4-treated Low Valent Lanthanide Particles (Sm and Yb)

1989 ◽  
Vol 18 (1) ◽  
pp. 171-172 ◽  
Author(s):  
Hayao Imamura ◽  
Kazuyoshi Koda ◽  
Hiroshi Miura ◽  
Susumu Tsuchiya
Keyword(s):  
Low Valent ◽  
Propylene Metathesis

scholarly journals Anatomy of gold catalysts: facts and myths

2015 ◽  
Vol 13 (26) ◽  
pp. 7103-7118 ◽  
Author(s):  
Beatrice Ranieri ◽  
Imma Escofet ◽  
Antonio M. Echavarren
Keyword(s):  
Organic Synthesis ◽  
Gold Catalysts ◽  
Review Article ◽  
Catalyst Activation

This review article covers the main types of gold(i) complexes used as precatalysts under homogeneous conditions in organic synthesis and discusses the different ways of catalyst activation as well as ligand, silver, and anion effects.

Peculiarities of propylene metathesis over catalysts prepared by anchoring of Mo(V) oxalate to γ-Al2O3

1990 ◽  
Vol 41 (1) ◽  
pp. 135-139 ◽  
Author(s):  
O. V. Klimov ◽  
A. N. Startsev
Keyword(s):  
Propylene Metathesis

scholarly journals Inside Back Cover: Copper Catalyst Activation Driven by Photoinduced Electron Transfer: A Prototype Photolatent Click Catalyst (Angew. Chem. Int. Ed. 29/2012)

2012 ◽  
Vol 51 (29) ◽  
pp. 7333-7333
Author(s):  
Lydie Harmand ◽  
Sarah Cadet ◽  
Brice Kauffmann ◽  
Luca Scarpantonio ◽  
Pinar Batat ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Photoinduced Electron Transfer ◽  
Copper Catalyst ◽  
Catalyst Activation ◽  
Back Cover
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