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Related Concept Videos

Factors Affecting Solubility04:01

Factors Affecting Solubility

Compared with pure water, the solubility of an ionic compound is less in aqueous solutions containing a common ion (one also produced by dissolution of the ionic compound). This is an example of a phenomenon known as the common ion effect, which is a consequence of the law of mass action that may be explained using Le Chȃtelier’s principle. Consider the dissolution of silver iodide:
Metal-Ligand Bonds02:51

Metal-Ligand Bonds

The hemoglobin in the blood, the chlorophyll in green plants, vitamin B-12, and the catalyst used in the manufacture of polyethylene all contain coordination compounds. Ions of the metals, especially the transition metals, are likely to form complexes.
In these complexes, transition metals form coordinate covalent bonds, a kind of Lewis acid-base interaction in which both of the electrons in the bond are contributed by a donor (Lewis base) to an electron acceptor (Lewis acid). The Lewis acid in...
Ionic Strength: Effects on Chemical Equilibria01:19

Ionic Strength: Effects on Chemical Equilibria

The addition of an inert ionic compound increases the solubility of a sparingly soluble salt. For example, adding potassium nitrate to a saturated solution of calcium sulfate significantly enhances the solubility of calcium sulfate. Le Châtelier's principle cannot predict this shift in the equilibrium. Instead, this could be explained in terms of changes in the effective concentration of the ions in solution in the presence of added inert salt.
In this solution, the primary cation—the calcium...
Potentiometry: Membrane Electrodes01:15

Potentiometry: Membrane Electrodes

Membrane electrodes, also known as p-ion electrodes, use membranes that selectively interact with free analyte ions, generating a potential difference across the membrane. The resulting membrane potential, known as the asymmetry potential, is not zero even when analyte concentrations on both sides of the membrane are equal. The membrane's response is typically not selective to a single analyte but proportional to the concentration of all ions in the sample solution capable of interacting at the...
Imperfections in Crystal Structure: Stoichiometric Point Defects01:26

Imperfections in Crystal Structure: Stoichiometric Point Defects

Schottky defects arise when some lattice points in a crystal, such as those in NaCl, remain unoccupied, creating lattice vacancies without disturbing the overall electrical neutrality of the crystal. This defect is common in ionic crystals where the positive and negative ions are similar in size, as seen in sodium chloride and cesium chloride. The presence of Schottky defects enables the crystal to conduct electricity to a small extent through an ionic mechanism. Electric fields cause nearby...
Imperfections in Crystal Structure: Non-Stoichiometric Defects01:29

Imperfections in Crystal Structure: Non-Stoichiometric Defects

Non-stoichiometric defects refer to a type of defect in the crystal structure of a compound where the ratio of its constituent elements deviates from the ideal stoichiometric ratio. There are two main types of non-stoichiometric defects: metal excess defects and metal deficiency defects.Metal excess defects occur when there is a slight surplus of metal ions than what is required by the stoichiometric ratio of the compound. For example, heating a sodium chloride crystal in sodium vapor results...

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Hydrophobic Salt-modified Nafion for Enzyme Immobilization and Stabilization
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Solid-state defect mechanism in vanadyl pyrophosphate catalysts: implications for selective oxidation.

P L Gai, K Kourtakis

    Science (New York, N.Y.)
    |February 3, 1995
    PubMed
    Summary

    Vanadyl pyrophosphate catalysts undergo surface structure modifications, forming defects via a glide shear mechanism. These defects, featuring anion vacancies, are crucial for activating alkanes like n-butane in catalytic dehydrogenation reactions.

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    Area of Science:

    • Materials Science
    • Catalysis
    • Surface Chemistry

    Background:

    • Vanadyl pyrophosphate is a key catalyst for alkane dehydrogenation.
    • Understanding catalyst surface modifications is crucial for optimizing performance.
    • Previous studies lacked detailed insights into defect formation mechanisms.

    Purpose of the Study:

    • To investigate the in situ structural modifications of vanadyl pyrophosphate catalysts.
    • To elucidate the mechanism of defect formation during alkane reaction.
    • To identify the role of these defects in alkane activation.

    Main Methods:

    • High-resolution in situ electron microscopy was employed.
    • Catalysts were reacted under alkane (n-butane) and reducing environments.
    • Defect analysis was performed using advanced microscopy techniques.

    Main Results:

    • Observed surface structure modifications with two sets of symmetry-related extended defects.
    • Identified defect formation via a pure (glide) shear mechanism.
    • Revealed basal anion vacancies linked to Lewis acid centers in the active plane.

    Conclusions:

    • The identified glide shear mechanism explains defect formation in vanadyl pyrophosphate.
    • Basal anion vacancies associated with Lewis acid centers are implicated in alkane activation.
    • These in-plane defect sites are potentially key to catalytic dehydrogenation of alkanes.