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Related Concept Videos

Heterogeneous Catalysis01:22

Heterogeneous Catalysis

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...
Passive Diffusion: Overview and Kinetics01:17

Passive Diffusion: Overview and Kinetics

Passive diffusion is a critical process that allows small lipophilic drugs to cross the cell membrane along a concentration gradient. This mechanism's efficiency depends on four primary factors: the membrane's surface area, the drug's lipid-water partition coefficient, the concentration gradient, and the membrane's thickness.
When administered orally, drugs establish a substantial concentration gradient between the gastrointestinal (GI) lumen and the bloodstream, expediting their diffusion into...
Diffusion01:21

Diffusion

Diffusion is a type of passive transport. In passive transport, a substance tends to move from an area of high concentration to an area of low concentration until the concentration is equal across the space. For example, take the diffusion of substances through the air. When someone opens a perfume bottle in a room filled with people, the perfume is at its highest concentration in the bottle and is at its lowest at the edges of the room. The perfume vapor will diffuse, or spread away, from the...
Diffusion01:12

Diffusion

Diffusion is the passive movement of substances down their concentration gradients—requiring no expenditure of cellular energy. Substances, such as molecules or ions, diffuse from an area of high concentration to an area of low concentration in the cytosol or across membranes. Eventually, the concentration will even out, with the substance moving randomly but causing no net change in concentration. Such a state is called dynamic equilibrium, which is essential for maintaining overall...
Catalysis02:50

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.
Catalysis01:27

Catalysis

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...

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Related Experiment Video

Updated: Jun 15, 2026

In Situ Monitoring of Diffusion of Guest Molecules in Porous Media Using Electron Paramagnetic Resonance Imaging
06:34

In Situ Monitoring of Diffusion of Guest Molecules in Porous Media Using Electron Paramagnetic Resonance Imaging

Published on: September 2, 2016

Surface diffusion in porous catalysts.

Daniel Weber1, Andrew J Sederman, Michael D Mantle

  • 1Department of Chemical Engineering and Biotechnology, University of Cambridge, Pembroke Street, Cambridge, UK CB2 3RA.

Physical Chemistry Chemical Physics : PCCP
|March 5, 2010
PubMed
Summary
This summary is machine-generated.

Pulsed field gradient nuclear magnetic resonance (NMR) uniquely identifies surface diffusion of 1-octene in porous catalysts. This method reveals molecular dynamics influenced by surface hydroxyl groups, advancing understanding of transport in heterogeneous catalysis.

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Synthesis and Catalytic Performance of Gold Intercalated in the Walls of Mesoporous Silica
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Last Updated: Jun 15, 2026

In Situ Monitoring of Diffusion of Guest Molecules in Porous Media Using Electron Paramagnetic Resonance Imaging
06:34

In Situ Monitoring of Diffusion of Guest Molecules in Porous Media Using Electron Paramagnetic Resonance Imaging

Published on: September 2, 2016

Imine Metathesis by Silica-Supported Catalysts Using the Methodology of Surface Organometallic Chemistry
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Imine Metathesis by Silica-Supported Catalysts Using the Methodology of Surface Organometallic Chemistry

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Synthesis and Catalytic Performance of Gold Intercalated in the Walls of Mesoporous Silica
11:02

Synthesis and Catalytic Performance of Gold Intercalated in the Walls of Mesoporous Silica

Published on: July 9, 2015

Area of Science:

  • Physical Chemistry
  • Materials Science
  • Catalysis

Background:

  • Understanding molecular transport in porous materials is crucial for heterogeneous catalysis.
  • Pore surface diffusion significantly impacts reaction rates and selectivity.
  • Characterizing surface diffusion dynamics requires advanced analytical techniques.

Purpose of the Study:

  • To apply pulsed field gradient nuclear magnetic resonance (PFG-NMR) for observing surface diffusion of 1-octene.
  • To unambiguously identify and quantify surface diffusion in porous catalysts.
  • To investigate the influence of surface properties on molecular transport.

Main Methods:

  • Utilizing PFG-NMR spectroscopy to probe molecular motion.
  • Applying a two-site exchange model to analyze diffusion regimes.
  • Comparing diffusion in untreated and silane-coated Pd/theta-Al(2)O(3) catalyst trilobes.

Main Results:

  • Distinct bulk pore and pore surface diffusion regimes of 1-octene were identified.
  • Diffusion coefficients for bulk and surface diffusion were determined (1.3 x 10(-9) and 1.7 x 10(-11) m(2) s(-1)).
  • Silane coating eliminated surface diffusion, indicating strong interaction with hydroxyl groups.

Conclusions:

  • PFG-NMR is a powerful technique for studying surface diffusion in porous media.
  • Surface diffusion is strongly influenced by interactions with hydroxyl groups on catalyst surfaces.
  • This method enhances understanding of liquid-phase heterogeneous catalytic processes.