In Situ and Ex Situ Microscopic Study of Propylene Polymerization With Heterogeneous Mgcl2-Supported Ziegler-Natta Catalysts

The large-scale commercial production of polyolefins by catalytic Ziegler-Natta polymerization have stimulated the development of the third, fourth and fifth generation heterogeneous catalysts comprising high surface area defective MgCl2 with TiCl4, electron donors, and AlR3-co-catalysts. In spite of intensive research over the years, the present level of understanding of the catalysts is still incomplete because of their complex composition leading to a multitude of local active site environments. The aim of this work is to provide a new insight into the process via in situ video microscopy of gas phase propylene polymerization over MgCl2-supported Ziegler-Natta catalysts combined with ex situ characterization by light and electron microscopy techniques (SEM, TEM, HRTEM, STEM, PEELS and windowless EDX). Procedures for catalyst synthesis are described elsewhere. The catalysts were stored in a dry box under a He atmosphere (<lppm H2O/O2). Samples were transferred to specimen holders in the dry box and then transferred into the microscopes under high purge N2 conditions to prevent poisoning of the catalysts by air and moisture.

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Electrochemically scrambled nanocrystals are catalytically active for CO2-to-multicarbons

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1918602117 ◽

2020 ◽

Vol 117 (17) ◽

pp. 9194-9201 ◽

Cited By ~ 9

Author(s):

Yifan Li ◽

Dohyung Kim ◽

Sheena Louisia ◽

Chenlu Xie ◽

Qiao Kong ◽

...

Keyword(s):

Structural Characteristics ◽

High Surface ◽

High Surface Area ◽

High Mobility ◽

Ex Situ ◽

Intrinsic Activity ◽

Air Exposure ◽

Disordered Structures ◽

Catalytically Active

Promotion of C–C bonds is one of the key fundamental questions in the field of CO2 electroreduction. Much progress has occurred in developing bulk-derived Cu-based electrodes for CO2-to-multicarbons (CO2-to-C2+), especially in the widely studied class of high-surface-area “oxide-derived” copper. However, fundamental understanding into the structural characteristics responsible for efficient C–C formation is restricted by the intrinsic activity of these catalysts often being comparable to polycrystalline copper foil. By closely probing a Cu nanoparticle (NP) ensemble catalyst active for CO2-to-C2+, we show that bias-induced rapid fusion or “electrochemical scrambling” of Cu NPs creates disordered structures intrinsically active for low overpotential C2+ formation, exhibiting around sevenfold enhancement in C2+ turnover over crystalline Cu. Integrating ex situ, passivated ex situ, and in situ analyses reveals that the scrambled state exhibits several structural signatures: a distinct transition to single-crystal Cu2O cubes upon air exposure, low crystallinity upon passivation, and high mobility under bias. These findings suggest that disordered copper structures facilitate C–C bond formation from CO2 and that electrochemical nanocrystal scrambling is an avenue toward creating such catalysts.

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Ex Situ and In Situ Synthesis and Characterization of Nickel Nanoparticles on High Surface Area Silica Support

Microscopy and Microanalysis ◽

10.1017/s1431927608085796 ◽

2008 ◽

Vol 14 (S2) ◽

pp. 282-283 ◽

Cited By ~ 1

Author(s):

R Banerjee ◽

PA Crozier

Keyword(s):

New Mexico ◽

Nickel Nanoparticles ◽

High Surface ◽

High Surface Area ◽

In Situ Synthesis ◽

Ex Situ ◽

Synthesis And Characterization ◽

Silica Support

Extended abstract of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008

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In situ and ex situ Moessbauer spectroscopy studies of iron phthalocyanine adsorbed on high surface area carbon

The Journal of Physical Chemistry ◽

10.1021/j100229a008 ◽

1983 ◽

Vol 87 (6) ◽

pp. 932-943 ◽

Cited By ~ 34

Author(s):

D. A. Scherson ◽

S. B. Yao ◽

E. B. Yeager ◽

J. Eldridge ◽

M. E. Kordesch ◽

...

Keyword(s):

Surface Area ◽

High Surface ◽

High Surface Area ◽

Ex Situ ◽

Iron Phthalocyanine ◽

Moessbauer Spectroscopy ◽

Spectroscopy Studies

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Atomic Layer Deposition of ZnO on Mesoporous Silica: Insights into Growth Behavior of ZnO via In-Situ Thermogravimetric Analysis

Nanomaterials ◽

10.3390/nano10050981 ◽

2020 ◽

Vol 10 (5) ◽

pp. 981 ◽

Cited By ~ 2

Author(s):

Piyush Ingale ◽

Kristian Knemeyer ◽

Mar Piernavieja Hermida ◽

Raoul Naumann d’Alnoncourt ◽

Arne Thomas ◽

...

Keyword(s):

Thermogravimetric Analysis ◽

Atomic Layer Deposition ◽

Reaction Mechanisms ◽

High Surface ◽

High Surface Area ◽

Atomic Layer ◽

Ex Situ ◽

Direct Access ◽

Layer Deposition

ZnO is a remarkable material with many applications in electronics and catalysis. Atomic layer deposition (ALD) of ZnO on flat substrates is an industrially applied and well-known process. Various studies describe the growth of ZnO layers on flat substrates. However, the growth characteristics and reaction mechanisms of atomic layer deposition of ZnO on mesoporous powders have not been well studied. This study investigates the ZnO ALD process based on diethylzinc (DEZn) and water with silica powder as substrate. In-situ thermogravimetric analysis gives direct access to the growth rates and reaction mechanisms of this process. Ex-situ analytics, e.g., N2 sorption analysis, XRD, XRF, HRTEM, and STEM-EDX mapping, confirm deposition of homogenous and thin films of ZnO on SiO2. In summary, this study offers new insights into the fundamentals of an ALD process on high surface area powders.

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Synthesis of heterogeneous catalysts with well shaped platinum particles to control reaction selectivity

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.0805691105 ◽

2008 ◽

Vol 105 (40) ◽

pp. 15241-15246 ◽

Cited By ~ 198

Author(s):

Ilkeun Lee ◽

Ricardo Morales ◽

Manuel A. Albiter ◽

Francisco Zaera

Keyword(s):

Surface Area ◽

Heterogeneous Catalysts ◽

Colloidal Particles ◽

Supported Catalysts ◽

High Surface ◽

Sol Gel ◽

High Surface Area ◽

Metal Particles ◽

Platinum Particles

Colloidal and sol-gel procedures have been used to prepare heterogeneous catalysts consisting of platinum metal particles with narrow size distributions and well defined shapes dispersed on high-surface-area silica supports. The overall procedure was developed in three stages. First, tetrahedral and cubic colloidal metal particles were prepared in solution by using a procedure derived from that reported by El-Sayed and coworkers [Ahmadi TS, Wang ZL, Green TC, Henglein A, El-Sayed MA (1996) Science 272:1924–1926]. This method allowed size and shape to be controlled independently. Next, the colloidal particles were dispersed onto high-surface-area solids. Three approaches were attempted: (i) in situ reduction of the colloidal mixture in the presence of the support, (ii) in situ sol-gel synthesis of the support in the presence of the colloidal particles, and (iii) direct impregnation of the particles onto the support. Finally, the resulting catalysts were activated and tested for the promotion of carbon–carbon double-bond cis-trans isomerization reactions in olefins. Our results indicate that the selectivity of the reaction may be controlled by using supported catalysts with appropriate metal particle shapes.

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Recent Catalysts Used in the Synthesis of 1,4-Disubstituted 1,2,3-Triazoles by Heterogeneous and Homogeneous Methods

Current Organic Chemistry ◽

10.2174/1385272824666200226120135 ◽

2020 ◽

Vol 24 (5) ◽

pp. 536-549

Author(s):

Saúl Noriega ◽

Elisa Leyva ◽

Edgar Moctezuma ◽

Luisa Flores ◽

Silvia Loredo-Carrillo

Keyword(s):

Heterogeneous Catalysts ◽

Phase Transfer ◽

High Surface ◽

High Surface Area ◽

Reducing Agent ◽

Dual Function ◽

Green Solvents ◽

Disubstituted Derivative ◽

Material Sciences

1,2,3-triazoles are popular heterocycles employed in material sciences and medicinal chemistry as they show antiviral, antibacterial, anti-HIV, antitubercular, and antifungal activities. Triazoles are appealing due to their stability and interesting click chemistry properties. The Cu(I) catalyzed reaction between azides and alkynes affords the 1,4- disubstituted derivative exclusively becoming a useful synthetic tool. However, one of the main drawbacks of the catalyzed reaction is the need to use Cu(I), which is unstable at standard conditions and rapidly oxidizes to the non-active Cu(II). The most common approach when synthesizing 1,4-disubstituted-1,2,3-triazoles is to reduce Cu in situ employing inorganic Cu salts and a reducing agent. The resulting Cu(I) needs to be further stabilized with organic ligands for the reaction to take place. The aim of homogeneous catalysis is to produce a ligand with a dual function both in reducing and stabilizing Cu(I) without interfering in the overall reaction. Instead, heterogeneous catalysis offers more options when supporting Cu on nanoparticles, complexes, and composites yielding the desired 1,2,3-triazoles in most cases without the need of a reducing agent under green solvents such as ethanol and water. The catalytic activity of Ag, Ru, and Ce is also discussed. This review exemplifies how the use of homogeneous and heterogeneous catalysts offers new and green methodologies for the synthesis of 1,2,3-triazole derivatives. The materials supporting Cu show catalytic properties like high surface area, acid-base sites or phase transfer. Although there is no ideal catalyst, Cu remains the most effective metal since it is economical, abundant and readily available.

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In Situ Nanoscale Studies of Liquid Polymerization Reactions in the Manufacture of Polyamides and.Combinatorial Catalysis

Microscopy and Microanalysis ◽

10.1017/s1431927600031378 ◽

2001 ◽

Vol 7 (S2) ◽

pp. 1060-1061

Author(s):

Pratibha L. Gai ◽

K. Kourtakis ◽

S. Ziemecki

Keyword(s):

Low Temperature ◽

Heterogeneous Catalysts ◽

High Surface ◽

Sol Gel ◽

High Surface Area ◽

Single Step ◽

Heterogeneous Catalytic ◽

Rutile Titania ◽

Real Time Information

Low temperature heterogeneous catalytic routes for polymers are of considerable interest in the chemical sciences and technology because they are economical and environmentally beneficial. However such routes have been difficult because of an incomplete understanding of process control and low yields. Currently, hydrogenation of aliphatic dintriles in solvents is used in the chemical industry to manufacture the corresponding diamenes which are subsequently reacted with adipic acid solutions and polymerized to produce the polyamide, nylon (6,6).Here we report an alternative, low temperature heterogeneous catalytic process for the polymerization reactions using novel environmental-HRTEM (EHREM) in liquid environments. EHREM under simulated reaction conditions provides direct, in situ real-time information on the dynamic structural and chemical changes and reaction modes of operation. We prepared high surface area heterogeneous catalysts including cobalt-ruthenium nanoclusters supported on rutile titania using a single step sol-gel technique, (shown in Fig. 1).

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Electron holography of catalysts

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100138452 ◽

1995 ◽

Vol 53 ◽

pp. 416-417

Author(s):

A. K. Datye ◽

D. S. Kalakkad ◽

L. F. Allard ◽

E. Völkl

Keyword(s):

Heterogeneous Catalysts ◽

High Surface ◽

High Surface Area ◽

Atomic Scale ◽

Nano Particles ◽

Phase Image ◽

Electron Holography ◽

Specimen Thickness ◽

Phase Information ◽

Particle Structure

The active phase in heterogeneous catalysts consists of nanometer-sized metal or oxide particles dispersed within the tortuous pore structure of a high surface area matrix. Such catalysts are extensively used for controlling emissions from automobile exhausts or in industrial processes such as the refining of crude oil to produce gasoline. The morphology of these nano-particles is of great interest to catalytic chemists since it affects the activity and selectivity for a class of reactions known as structure-sensitive reactions. In this paper, we describe some of the challenges in the study of heterogeneous catalysts, and provide examples of how electron holography can help in extracting details of particle structure and morphology on an atomic scale.Conventional high-resolution TEM imaging methods permit the image intensity to be recorded, but the phase information in the complex image wave is lost. However, it is the phase information which is sensitive at the atomic scale to changes in specimen thickness and composition, and thus analysis of the phase image can yield important information on morphological details at the nanometer level.

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