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Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation

Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation

Introduction
Like alkenes, alkynes can be reduced to alkanes in the presence of transition metal catalysts such as Pt, Pd, or Ni. The reaction involves two sequential syn additions of hydrogen via a cis-alkene intermediate.

Reduction of Alkenes: Asymmetric Catalytic Hydrogenation

Reduction of Alkenes: Asymmetric Catalytic Hydrogenation

Catalytic hydrogenation of alkenes is a transition-metal catalyzed reduction of the double bond using molecular hydrogen to give alkanes. The mode of hydrogen addition follows syn stereochemistry.
The metal catalyst used can be either heterogeneous or homogeneous. When hydrogenation of an alkene generates a chiral center, a pair of enantiomeric products is expected to form. However, an enantiomeric excess of one of the products can be facilitated using an enantioselective reaction or an...

Reduction of Alkenes: Catalytic Hydrogenation

Reduction of Alkenes: Catalytic Hydrogenation

Alkenes undergo reduction by the addition of molecular hydrogen to give alkanes. Because the process generally occurs in the presence of a transition-metal catalyst, the reaction is called catalytic hydrogenation.
Metals like palladium, platinum, and nickel are commonly used in their solid forms — fine powder on an inert surface. As these catalysts remain insoluble in the reaction mixture, they are referred to as heterogeneous catalysts.
The hydrogenation process takes place on the...

[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction

[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction

The Diels–Alder reaction is an example of a thermal pericyclic reaction between a conjugated diene and an alkene or alkyne, commonly referred to as a dienophile. The reaction involves a concerted movement of six π electrons, four from the diene and two from the dienophile, forming an unsaturated six-membered ring. As a result, these reactions are classified as [4+2] cycloadditions.

Catalysis

Catalysis

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.

Resonance and Hybrid Structures

Resonance and Hybrid Structures

According to the theory of resonance, if two or more Lewis structures with the same arrangement of atoms can be written for a molecule, ion, or radical, the actual distribution of electrons is an average of that shown by the various Lewis structures.
Resonance Structures and Resonance Hybrids
The Lewis structure of a nitrite anion (NO2−) may actually be drawn in two different ways, distinguished by the locations of the N–O and N=O bonds.

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Synthesis and Performance Characterizations of Transition Metal Single Atom Catalyst for Electrochemical CO2 Reduction

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Decoding reactive structures in dilute alloy catalysts.

Nicholas Marcella¹, Jin Soo Lim², Anna M Płonka¹

¹Department of Materials Science and Chemical Engineering, Stony Brook University, Stony Brook, NY, 11794, USA.

Nature Communications

|February 12, 2022

Summary

This summary is machine-generated.

Researchers identified that small palladium (Pd) ensembles on gold (Au) nanoparticles are key active sites for hydrogen-deuterium exchange reactions. Catalyst pretreatment allows tuning of these Pd ensembles, optimizing catalytic activity for sustainable processes.

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Area of Science:

Materials Science
Catalysis
Surface Chemistry

Background:

Rational catalyst design is essential for energy-efficient and sustainable chemical processes.
Understanding dynamic active sites at the atomic level is critical for modeling catalytic reactions.
Dilute palladium-in-gold (Pd-in-Au) alloy nanoparticles are a model system for studying complex alloy catalysts.

Purpose of the Study:

To identify the specific active species responsible for catalysis in dilute Pd-in-Au alloy nanoparticles.
To correlate atomic-level structures with observed catalytic activity and spectroscopic data.
To demonstrate a method for tuning catalytic activity by controlling active site composition.

Main Methods:

Combines experimental catalytic activity measurements with advanced spectroscopic analysis.
Utilizes machine learning for spectroscopic data interpretation.
Employs first-principles based kinetic modeling to understand reaction pathways.
Investigates the effect of catalyst pretreatment on active site structure and performance.

Main Results:

Identifies small palladium ensembles (1-3 atoms) on the surface as the active sites for hydrogen-deuterium exchange.
Successfully explains observed X-ray spectra and apparent activation energy using these Pd ensembles.
Demonstrates that catalytic activity can be precisely tuned by controlling the size of Pd ensembles via pretreatment.
Confirms the dynamic nature of active sites in alloy catalysts.

Conclusions:

A data-driven, multimodal approach can decode reactive structures in complex alloy catalysts.
Precisely controlling the size of metal ensembles in alloy nanoparticles offers a pathway for on-demand tuning of catalytic activity.
This work provides fundamental insights into structure-activity relationships in heterogeneous catalysis, paving the way for more efficient catalyst design.