Bis(2-chloroethoxy)methane degradation by TiO2 photocatalysis: Parameter and reaction pathway investigations

Catalytic enhancement of chemical reactions via heterogeneous materials occurs through stabilization of transition states at designed active sites, but dramatically greater rate acceleration on that same active site is achieved when the surface intermediates oscillate in binding energy. The applied oscillation amplitude and frequency can accelerate reactions orders of magnitude above the catalytic rates of static systems, provided the active site dynamics are tuned to the natural frequencies of the surface chemistry. In this work, differences in the characteristics of parallel reactions are exploited via selective application of active site dynamics (0 < ΔU < 1.0 eV amplitude, 10<sup>-6</sup> < f < 10<sup>4</sup> Hz frequency) to control the extent of competing reactions occurring on the shared catalytic surface. Simulation of multiple parallel reaction systems with broad range of variation in chemical parameters revealed that parallel chemistries are highly tunable in selectivity between either pure product, even when specific products are not selectively produced under static conditions. Two mechanisms leading to dynamic selectivity control were identified: (i) surface thermodynamic control of one product species under strong binding conditions, or (ii) catalytic resonance of the kinetics of one reaction over the other. These dynamic parallel pathway control strategies applied to a host of chemical conditions indicate significant potential for improving the catalytic performance of many important industrial chemical reactions beyond their existing static performance.

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A Paramedic Treatment for Modeling Explicitly Solvated Chemical Reaction Mechanisms

10.26434/chemrxiv.6045422.v1 ◽

2018 ◽

Author(s):

Yasemin Basdogan ◽

John Keith

Keyword(s):

Reaction Mechanism ◽

Chemical Reaction ◽

Reaction Mechanisms ◽

Reaction Pathway ◽

Optimization Procedure ◽

Cost Effective ◽

Chemical Reaction Mechanisms ◽

Solvent Molecules ◽

Dynamics Simulations ◽

Mbh Reaction

<div> <div> <div> <p>We report a static quantum chemistry modeling treatment to study how solvent molecules affect chemical reaction mechanisms without dynamics simulations. This modeling scheme uses a global optimization procedure to identify low energy intermediate states with different numbers of explicit solvent molecules and then the growing string method to locate sequential transition states along a reaction pathway. Testing this approach on the acid-catalyzed Morita-Baylis-Hillman (MBH) reaction in methanol, we found a reaction mechanism that is consistent with both recent experiments and computationally intensive dynamics simulations with explicit solvation. In doing so, we explain unphysical pitfalls that obfuscate computational modeling that uses microsolvated reaction intermediates. This new paramedic approach can promisingly capture essential physical chemistry of the complicated and multistep MBH reaction mechanism, and the energy profiles found with this model appear reasonably insensitive to the level of theory used for energy calculations. Thus, it should be a useful and computationally cost-effective approach for modeling solvent mediated reaction mechanisms when dynamics simulations are not possible. </p> </div> </div> </div>

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Photocatalytic Alkylation of Pyrroles and Indoles with α-Diazo Esters

10.26434/chemrxiv.8230235 ◽

2019 ◽

Author(s):

Łukasz Ciszewski ◽

Jakub Durka ◽

Dorota Gryko

Keyword(s):

Aromatic Compounds ◽

Reaction Pathway ◽

Alkylating Agents ◽

Catalytic Amount ◽

Radical Formation ◽

Reaction Selectivity ◽

Diazo Esters ◽

Electron Withdrawing Substituents

This article describes direct photoalkylation of electron-rich aromatic compounds with diazo compoiunds. C-2 alkylated indoles and pyrroles are obtained with good yields even though the photocatalyst (Ru(bpy)3Cl2) loading is as low as 0.075 mol %. For substrates bearing electron-withdrawing substituents the addition of a catalytic amount of N,N-dimethyl-4-methoxyaniline is required. Both EWG-EWG and EWG-EDG substituted diazo esters are suitable as alkylating agents. The reaction selectivity and mechanistic experiments suggest that carbenes/carbenoid intermediates are not involved in the reaction pathway, instead radical formation is proposed.

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Superior co-catalysis by bimetallic nanostructure for TiO2 photocatalysis

Journal of Photocatalysis ◽

10.2174/2665976x01999201022194257 ◽

2020 ◽

Vol 01 ◽

Author(s):

Bonamali Pal ◽

Anila Monga ◽

Aadil Bathla

Keyword(s):

Visible Light ◽

Catalytic Performance ◽

Transition Metal Catalysts ◽

Core Shell ◽

Structural Morphology ◽

Tio2 Photocatalysis ◽

Co Catalysts ◽

Bimetallic Nanocomposites ◽

Bimetallic Nanostructure ◽

Bimetallic Nanostructures

Background:: Bimetallic nanocomposites have currently gained significant importance for enhanced catalytic applications relative to monometallic analogues. The synergistic interactions modified electronic and optical properties in the bimetallic (M1@M2) structural morphology e.g., core-shell /alloy nanostructures resulted in a better co-catalytic performance for TiO2 photocatalysis. Objective:: Hence, this article discusses the preparation, characterization, and co-catalytic activity of different bimetallic nanostructures namely, Cu@Zn, Pd@Au, Au@Ag, and Ag@Cu, etc. Method:: These bimetallic co-catalysts deposited on TiO2 possess the ability to absorb visible light due to surface plasmonic absorption and are also expected to display the new properties due to synergy between two distinct metals. As a result, they reveal the highest level of activity than the monometal deposited TiO2. Result:: Their optical absorption, emission, charge carrier dynamics, and surface structural morphology are explained for the improved photocatalytic activity of M1@M2 loaded TiO2 for the hydrogenation of certain organic compounds e.g., quinoline, crotonaldehyde, and 1,3-dinitrobenzene, etc. under UV/ visible light irradiation. Conclusion:: It revealed that the use of bimetallic core@shell co-catalyst for hydrogenation of important industrial organics by M1@M2-TiO2 nanocomposite demonstrates beneficial reactivity in many instances relative to conventional transition metal catalysts.

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The mechanism of formation of 2,7-dimethyl-2,6-octadiene in the synthesis of 3-methylene-7-methyl-1,6-octadiene

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19831864 ◽

1983 ◽

Vol 48 (7) ◽

pp. 1864-1866

Author(s):

Jan Bartoň ◽

Ivan Kmínek

Keyword(s):

Mass Spectrometry ◽

Nmr Spectroscopy ◽

Alkali Metal ◽

Chromatographic Analysis ◽

Solid Phase ◽

Reaction Pathway ◽

Mechanism Of Formation ◽

Gas Chromatographic Analysis ◽

C Nmr ◽

Visual Observations

2,7-Dimethyl-2,6-octadiene is formed in the catalytic solution for the dimerization of 2-methyl-1,3-butadiene to β-myrcene (3-methylene-7-methyl-1,6-octadiene), as revealed by mass spectrometry and 13C NMR spectroscopy. Visual observations together with the results of gas chromatographic analysis of the catalytic solution suggest that the formation of 2,7-dimethyl-2,6-octadiene is associated with the transition of the alkali metal (sodium) from the solid phase into the solution. A reaction pathway is suggested accounting for the formation of 2,7-dimethyl-2,6-octadiene in the system.

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