Video Experimental Relacionado
Updated: Jul 20, 2026
07:28
Ethylene Polymerizations Using Parallel Pressure Reactors and a Kinetic Analysis of Chain Transfer Polymerization
Published on: November 27, 2015
Catalizadores de titanio de un solo sitio con soporte de sílice para la epoxidación de olefinas. Una estrategia de
Jonggol Jarupatrakorn1, T Don Tilley
1Department of Chemistry, University of California, Berkeley, California 94720-1460, USA.
Journal of the American Chemical Society
|July 11, 2002
Resumen
Los investigadores desarrollaron catalizadores de epoxidación soportados por titanio altamente activos y selectivos utilizando un método de injerto de precursores moleculares. Los soportes de sílice mesoporosa como el SBA-15 mejoran el rendimiento del catalizador para la epoxidación del ciclohexeno.
Área de la Ciencia:
- Ciencia de los materiales Ciencia de los materiales.
- La catálisis es la catálisis.
- Nanotecnología La nanotecnología es la nanotecnología.
Sus antecedentes:
- El desarrollo de catalizadores eficientes y selectivos es crucial para la síntesis química.
- Los catalizadores a base de titanio son prometedores para las reacciones de oxidación.
- El aislamiento del sitio de las especies activas en soportes puede mejorar el rendimiento catalítico.
Objetivo del estudio:
- Para sintetizar catalizadores de epoxidación apoyados en titanio aislados en el sitio.
- Investigar la estructura y las propiedades catalíticas de estos nuevos catalizadores.
- Evaluar la influencia de los precursores moleculares y soportes de sílice en la actividad catalítica y la selectividad.
Principales métodos:
- Se empleó un enfoque de precursores moleculares utilizando complejos de titanio tris ((tert-butoxi) siloxi.
- Complejos de titanio injertados en soportes de Aerosil amorfo, MCM-41 mesoporoso y SBA-15 de sílice.
- Caracterizó las especies de titanio soportadas utilizando difracción de rayos X en polvo, adsorción / desorción de nitrógeno, espectroscopias infrarrojas y espectroscopias ultravioletas de reflectancia difusa.
Principales resultados:
- Produjo con éxito especies de titanio aisladas en el sitio, predominantemente coordinadas tetraédricamente en soportes de sílice.
- La actividad y la selectividad del catalizador aumentaron con la disminución de los ligandos de siloxido en el precursor.
- Las silicas mesoporosas (MCM-41, SBA-15) superaron a la sílice amorfa como soportes.
- TiSi3 apoyado en SBA-15 produjo catalizadores de epoxidación de ciclohexeno altamente activos con frecuencias de giro (TOF) de 500-1500 h{-1}.
Conclusiones:
- Los complejos de silóxido de titanio ricos en oxígeno son precursores moleculares efectivos para catalizadores de epoxidación con soporte.
- El aislamiento del sitio y la elección de soportes mesoporosos son factores clave para un alto rendimiento catalítico.
- Los catalizadores desarrollados muestran un potencial significativo para una epoxidación eficiente del ciclohexeno.
Videos de Conceptos Relacionados
02:50Catalysis
The presence of a catalyst affects the rate of a chemical reaction. A catalyst is a substance that can increase the reaction rate without being consumed during the process. A basic comprehension of a catalysts’ role during chemical reactions can be understood from the concept of reaction mechanisms and energy diagrams.
01:11ortho–para-Directing Activators: –CH3, –OH, –NH2, –OCH3
All ortho–para directors, excluding halogens, are activating groups. These groups donate electrons to the ring, making the ring carbons electron-rich. Consequently, the reactivity of the aromatic ring towards electrophilic substitution increases. For instance, the nitration of anisole is about 10,000 times faster than the nitration of benzene. The electron-donating effect of the methoxy group in anisole activates the ortho and para positions on the ring and stabilizes the corresponding...
01:13Olefin Metathesis Polymerization: Overview
Recently, the development of olefin metathesis polymerization advanced the field of polymer synthesis. Simply put, the reorganization of substituents on their double bonds between two olefins in the presence of a catalyst is known as the olefin metathesis reaction. The use of metathesis reaction for polymer synthesis is called olefin metathesis polymerization.
Ruthenium-based Grubbs catalyst is the most commonly used catalyst for olefin metathesis polymerization. Grubbs catalyst consists of a...
Ruthenium-based Grubbs catalyst is the most commonly used catalyst for olefin metathesis polymerization. Grubbs catalyst consists of a...
01:16Olefin Metathesis Polymerization: Ring-Opening Metathesis Polymerization (ROMP)
Ring-opening metathesis polymerization or ROMP involves strained cycloalkenes as starting materials. The mechanism of ROMP proceeds by reacting cycloalkene with Grubbs catalyst to give metallacyclobutane intermediate which undergoes a ring-opening reaction to form new carbene. The new carbene reacts with another molecule of cycloalkene. Repetition of these steps leads to the formation of an unsaturated open-chain polymer product. All these steps are reversible, however, relieving the ring...
00:53Olefin Metathesis Polymerization: Acyclic Diene Metathesis (ADMET)
Acyclic diene metathesis polymerization or ADMET polymerization involves cross-metathesis of terminal dienes, such as 1,8-nonadiene, to give linear unsaturated polymer and ethylene. As ADMET is a reversible process, the formed ethylene gas must be removed from the reaction mixture to complete the polymerization process.
Similar to cross-metathesis, ADMET also involves the formation of metallacyclobutane intermediate by [2+2] cycloaddition of one of the double bonds of a terminal diene with...
Similar to cross-metathesis, ADMET also involves the formation of metallacyclobutane intermediate by [2+2] cycloaddition of one of the double bonds of a terminal diene with...
01:27Catalysis
Catalysis influences the rate of chemical reactions by providing an alternative reaction pathway with lower activation energy. A catalyst speeds up a reaction, but it is not consumed during the process. The fundamental principle of catalysis is the ability of a catalyst to alter the reaction mechanism, often introducing a more efficient pathway than the uncatalyzed process.In a catalyzed reaction, the catalyst participates directly in the reaction mechanism. It interacts with reactants to form...