Reduction of metal oxide

Goldschmidt reaction The use of A1 powder for the reduction of metal oxides. 

Reduction of metal oxides with hydrogen is of interest in the metals refining industry (94,95) (see Metallurgy). Hydrogen is also used to reduce sulfites to sulfides in one step in the removal of SO2 pollutants (see Airpollution) (96). Hydrogen reacts directiy with SO2 under catalytic conditions to produce elemental sulfur and H2S (97—98). Under certain conditions, hydrogen reacts with nitric oxide, an atmospheric poUutant and contributor to photochemical smog, to produce N2 ... 

The manufacture of metal in powder form is a complex and highly engineered operation. It is dominated by the variables of the powder, namely those that are closely connected with an individual powder particle, those that refer to the mass of particles which form the powder, and those that refer to the voids in the particles themselves. In a mass of loosely piled powder, >60% of the volume consists of voids. The primary methods for the manufacture of metal powders are atomization, the reduction of metal oxides, and electrolytic deposition (15,16). Typical metal powder particle shapes are shown in Figure 5. 

Apart from the application of XPS in catalysis, the study of corrosion mechanisms and corrosion products is a major area of application. Special attention must be devoted to artifacts arising from X-ray irradiation. For example, reduction of metal oxides (e. g. CuO -> CU2O) can occur, loosely bound water or hydrates can be desorbed in the spectrometer vacuum, and hydroxides can decompose. Thorough investigations are supported by other surface-analytical and/or microscopic techniques, e.g. AFM, which is becoming increasingly important. 

Form metal catalysts by reduction of metal oxides with hydrogen. 

Elemental carbon has many important applications. The diamond is a precious gem, known to mankind for ages graphite is used as an electrode and has numerous other applications carbon-14 isotope is used in carbon dating and the isotope carbon-13 in tracer studies and NMR. Carbon black is used in paints, pigments and inks. Activated carbon is used as an adsorbent for purification of water and separation of gases. Coke is used for electrothermal reduction of metal oxides to their metals. These applications are discussed below in more detail. 

Equations (2.45) through (2.47) are typical oxidation reactions for the formation of metal oxides. The reverse reactions (steps g-a) are the reduction of metal oxides to form metal, such as is found in smelting operations. It should be apparent that the control of the oxygen partial pressure during heating is an important parameter in determining which phases will form. 

The free energy line for the formation of carbon monoxide and carbon dioxide are included in this plot, as the reduction of metal oxides with carbon monoxide is common in smelting operations ... 

Reduction of metal oxides, intercalated between the 72 clay layers (pillared clays), led to metal-intercalated clay nanocomposites... 

Reduction of metal oxides by other metals (Figure 10.6, p. 154). Demonstrate the Thermit reaction and the reactions between the metals magnesium, zinc, iron and copper and their oxides. This will establish an order of reactivity for these metals. Some of these reactions are very violent so the use of small quantities and a rehearsal before the class demonstration are essential. R... 

Reduction of metal oxides by methane/hydrogen. It is safer to use methane, which is passed over heated copper oxide. R... 

The rate constants, k, of Eq. (4) for the reduction of metal oxides of interest to fusion device wall materials (FeO, CrjO, TiO, etc.) have not been measured. However, the equilibrium... 

Metal Oxides. Reduction of metal oxides such as chromium(III) oxide, molybdenum trioxide, niobium pentoxide, tungsten trioxide, and vanadium pentoxide is violently exothermic and rapid.9... 

K. Tokumitsu, Reduction of Metal Oxides by Mechanical Alloying Method, Solid State Ionics,... 

G. B. Schaffer, P. G. McCormick, Reduction of Metal oxides by Mechanical Alloying, Appl. 

Figure 8 shows the vectors on the thermodynamic compass for typical endergonic reactions. It is found that for chemical reactions all three types can be observed. However, the most common one may be the heating type of which examples are the reduction of metallic oxides and the decomposition of water to hydrogen and oxygen. 

Both types of reactions involving the spillover of either H2 or 02 have been termed topochemical heterogeneous catalysis (62). Besides the catalyzed reduction of metal oxides either to metals or suboxides, the formation of new and specific reduced oxides, such as the well-known hydrogen bronzes of W, Mo, and V, have attracted considerable attention (7,66-68). In many cases the reduction of the corresponding oxides by spillover of H2 led to reduced compounds not otherwise obtainable (69). 

Desorption of water often converts Bronsted to Lewis acids, and readsorption of water can restore Bronsted acidity. Probe molecules, such as ammonia, pyridine, etc., are used to evaluate Bronsted and Lewis acidity. These compounds may contain water as an impurity, however. Water produced by reduction of metal oxides can also be readsorbed on acid sites. Probe molecules can in some cases react on surface acid sites, giving misleading information on the nature of the original site. Acidity, and accessibility, of hydroxyl groups or adsorbed water on zeolites and acidic oxides can vary widely. Study of adsorbed nitrogen bases is very useful in characterization of surface acid sites, but potential problems in the use of these probes should be kept in mind. 

Reduction of Metallic Oxides.—Hydrogen can displace many metals from their oxides, the reduction taking place at the ordinary temperature, as with silver and palladium oxides, or on heating, as with the oxides of copper, cadmium, lead, antimony, nickel, cobalt, and iron. Sometimes these reductions are incomplete, an equilibrium being attained. Such equilibria depend on the experimental conditions, an example being the action of steam on heated iron (p. 15). 

Fluid-solid reactions include thermal decomposition of minerals, roasting (oxidation) of sulfide ores, reduction of metal oxides with hydrogen, nitridation of metals, and carburization of metals. Each t3 e of reaction will be discussed finm the thermodynamic point of view. Then reaction kinetics for all of the various rate determining steps in fluid-sohd reactions will be discussed for two general models shrinking core and shrinking particle. 

The reduction of metal oxides (M Oy) by hydrogen gas is metallurgically valuable. Water is produced in this reaction ... 

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