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Related Concept Videos

Catalysis02:50

Catalysis

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Reduction of Alkenes: Catalytic Hydrogenation02:13

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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.
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Heterogeneous Catalysis01:22

Heterogeneous Catalysis

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Heterogeneous catalysis involves a catalyst in a different phase from the reactants. It is a process where the catalyst and the reactants are in distinct phases, typically solid and gas or liquid.Most heterogeneous catalysts are metals, metal oxides, or acids. The list includes transition metals like iron (Fe), cobalt (Co), nickel (Ni), palladium (Pd), platinum (Pt), chromium (Cr), manganese (Mn), tungsten (W), silver (Ag), and copper (Cu). These metals possess partially vacant d orbitals that...
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Reduction of Alkenes: Asymmetric Catalytic Hydrogenation02:17

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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.
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Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation02:24

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Introduction
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Reduction of Benzene to Cyclohexane: Catalytic Hydrogenation01:28

Reduction of Benzene to Cyclohexane: Catalytic Hydrogenation

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Unlike the easy catalytic hydrogenation of an alkene double bond, hydrogenation of a benzene double bond under similar reaction conditions does not take place easily. For example, in the reduction of stilbene, the benzene ring remains unaffected while the alkene bond gets reduced. Hydrogenation of an alkene double bond is exothermic and a favorable process. In contrast, to hydrogenate the first unsaturated bond of benzene, an energy input is needed; that is, the process is endothermic. This is...
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A Simple, Low-cost, and Robust System to Measure the Volume of Hydrogen Evolved by Chemical Reactions with Aqueous Solutions
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Catalyst support effects on hydrogen spillover.

Waiz Karim1,2,3, Clelia Spreafico4, Armin Kleibert5

  • 1Institute for Chemical and Bioengineering, ETH Zurich, 8093 Zurich, Switzerland.

Nature
|January 6, 2017
PubMed
Summary
This summary is machine-generated.

Hydrogen spillover, the movement of activated hydrogen atoms, occurs rapidly on reducible titanium oxide supports but is significantly slower and limited on nonreducible aluminium oxide supports. This study quantizes spillover efficiency on different catalyst supports.

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Area of Science:

  • Materials Science
  • Surface Chemistry
  • Catalysis

Background:

  • Hydrogen spillover is the migration of activated hydrogen from metal catalysts to supports.
  • Its occurrence on reducible supports like titanium oxide is known, but its behavior on nonreducible supports like aluminium oxide remains unclear.

Purpose of the Study:

  • To quantify the efficiency and spatial extent of hydrogen spillover on both reducible (titanium oxide) and nonreducible (aluminium oxide) supports.
  • To investigate the mechanisms of hydrogen spillover on different catalyst supports using precisely engineered model systems.

Main Methods:

  • Fabrication of model catalyst systems with controlled nanoparticle spacing (0-45 nm) using top-down nanofabrication.
  • In situ X-ray absorption spectromicroscopy to observe the reduction of iron oxide nanoparticles by hydrogen generated on platinum nanoparticles.
  • Density functional theory calculations to elucidate spillover mechanisms.

Main Results:

  • Fast hydrogen spillover was observed on titanium oxide, reducing remote iron oxide nanoparticles via proton-electron transfer.
  • Spillover on aluminium oxide is ten orders of magnitude slower and spatially restricted, mediated by interactions with three-coordinated aluminium centers and water.
  • Desorption competes with hydrogen mobility on aluminium oxide.

Conclusions:

  • The study clarifies the differing mechanisms and efficiencies of hydrogen spillover on reducible versus nonreducible oxide supports.
  • Findings enhance understanding of hydrogen storage and catalytic reactions, providing insights into synergistic effects in multi-functional catalysts.
  • The developed model system approach offers a platform for studying supported catalyst functionalities.