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Metal Oxide

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Metal oxides are fundamentally important as heterogeneous industrial catalysts - either as stand alone catalysts or in combination with other oxides or metals. Metal oxides interfaces have been in the focus of applied and fundamental research for many years due to their relevance in many different fields such as material science, catalysis, sensors and microelectronics.

In recent years numerous types of metal oxides in particulate film or composite forms have become key components in catalysis, solid oxide fuel cells and sensing devices. More recently metal oxides nanoparticles have been used in a variety of biomedical applications due to the high surface area and enhanced magnetic and catalytic activity. 

Definition

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Many synthetic routes for preparing transition metal oxide catalysts produce a supported metal oxide structure consisting of an active metal oxide phase dispersed on a second high surface area oxide. IUPAC defines the surface density as mass per unit area. For supported metal oxides this is vaguely interpreted as the amount of supported metal oxide active phase per surface area underlying oxide support.

This broad definition allows considerable latitude in whether total or exposed surface area is of the uncovered support or final catalyst. The surface oxide generally exists in several different molecular and nano scale structures depending on the surface density range. The formation of these structures depends on the supported metal oxide content of the catalyst and the support layer interactions and also on the synthesis route support surface area and calcination conditions.

Formula

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Though the use of chemical symbols and numerical subscripts the formula of a compound can be written. The simplest formula that may be written is the empirical formula. In this formula, the subscripts are in the form of the simplest whole number ratio of the atoms in a molecule or of the ions in a formula unit. The molecular formula however represents the actual number of atoms in a molecule.

Follow these steps for writing a chemical formula of a metal oxide.

Step 1: Write the symbols of the constituent elements or radicals that combines to form a molecule of a the compound.
Step 2: Write down the valencies of the elements or radicals as superscripts on the respective elements or radicals.
Step 3: Interchange the valencies of the elements or radicals and write down these numbers as subscripts.
Step 4: If the valencies are divisible by a common number, simplify the numbers in the subscript; otherwise retain them as such.
Step 5: If two or more units of a radical are involved, then the radical is enclosed within brackets and the number representing the units is written as subscript outside the bracket.

Example

Barium oxide

Step 1: Write the symbols of the constituent element - BaO4.
Step 2: Write the valencies as superscripts Ba2O2.
Step 3: Interchange the valencies and write then as subscripts. Reduce the valencies to the lowest order by cancelling by the common factor, that is $\frac{2}{2}$ = 1. So it becomes Ba1O1.
Step 4: The valency 1 need not be written, So write it as BaO.

Non Metal Oxide

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Most oxides exhibit acidic or basic properties. These properties become apparent when the oxide reacts with an acid or base and in some cases when the oxide reacts with water.

Most nonmetal oxides are acidic oxides. An acid anhydride produces an acid when added to water. A few nonmetal oxides, such as CO and NO dont react. Usually when a nonmetal oxide reacts, it forms only a simple acid, and the nonmetal in the same oxidation state.

Equations for the reactions of phosphorus and sulfur with oxygen are shown below.

P4(s) + 5O2(g) $\overset{white\ flame}{\rightarrow}$ P4O10 (s)
S(s) + O2(g) $\overset{blue\ flame}{\rightarrow}$ SO2(g)

Transition Metal Oxide

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Transition metal oxides offer an additional dimension for chemisorption compared to non-transition metal oxides in that the number of electrons on the metal cations can be changed relatively easily. Also it is often possible to reduce the surface of a transition metal oxide to a lower oxide upon chemisorption, something that is generally impossible for non-transition metal oxides. One of the most important driving forces for the study of metal transition oxide surface interactions over the last decade or so has been the strong catalyst metal/ support interactions.

The transition metal oxides are of particular interest for applications in catalysis, sensor materials and other potential applications. Indeed metal oxides are the key components for a variety of catalytic reactions functioning directly as reactive components or as supports for dispersed active metal species, or as additives or promoters to enhance the rate of catalytic reactions.

List 

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It has been known for a long time that metal oxides can vary in their semi-conductor properties depending on the type of gas atmosphere in which they are placed. The use of metal oxides such as gas sensitive materials was initiated in the 1960. Around the same period the variation in electrical resistance in a ZnO film allowed the detection of reductor gases.

The list of metal oxides includes ZnO, CuO, Al2O3, La2O3, Fe2O3, SnO2 and TiO2. The results indicated that the cytotoxicity decreased with the increase in the cation charge.