Reduced metal oxide

Ammonia will reduce metallic oxides which are reduced by hydrogen (for example copper(II) oxide, CuO, lead(II) oxide, PbO), being itself oxidised to nitrogen ... 

The process can be operated in two modes co-fed and redox. The co-fed mode employs addition of O2 to the methane/natural gas feed and subsequent conversion over a metal oxide catalyst. The redox mode requires the oxidant to be from the lattice oxygen of a reducible metal oxide in the reactor bed. After methane oxidation has consumed nearly all the lattice oxygen, the reduced metal oxide is reoxidized using an air stream. Both methods have processing advantages and disadvantages. In all cases, however, the process is mn to maximize production of the more desired ethylene product. 

Carbon and Hydrogen.—Carbon compounds are frequently inflammable, and when heated on platinum foil take fipe or char and burn away. A safer test is to heat the substance with some easily reducible metallic oxide, the oxygen of which forms carbon diovide with the carbon present. Take a piece of soft glass tube about 13 cm. (5 in.) long, and fuse it together at one end. Heat a gram or two of fine copper oxide in a porcelain crucible for a few minutes to drive off the moisture, and let it cool in a desiccator. Mix it with about one-tenth of its bulk of powdered sugar in a mortar. Pour the mixture into the tube, the open end of which is now drawn out into a wide capillary and oeni. at the same time into the form Fig. i. 

Erythorbic acid and sodium erythorbate are very safe products, widely used in the food industry as antioxidants and alternatives to vitamin C. In the water treatment industry, they are strong reducing agents that reduce metal oxides and hydroxides to their more soluble ferrous forms and promote the passivation of boiler waterside surfaces (magnetite formation). 

AES is a useful element-specific technique for quantitative determination of the elemental composition of a surface. Although some chemical information is available in principle, the technique is used largely for elemental analysis. Electron beam damage can decompose organic adsorbates and cause damage, particularly on insulating surfaces. In some cases, the beam can reduce metal oxides. 

Active gold catalysts are advantageous in that water usually enhances the catalytic activity [39]. Reducible or semiconductive metal oxide supports do not need moisture for room temperature catalytic activity, while non-reducible metal oxides such as AI2O3 and Si02 do [39] (Figure 10). 

Lithium is used to reduce metallic oxides in metallurgical operations, and the reactions, after initiation at moderate temperatures, are violently exothermic and rapid. Chromium(III) oxide reacts at 185°C, reaching 965° similarly molybdenum trioxide (180 to 1400°), niobium pentoxide (320 to 490°), titanium dioxide (200-400 to 1400°), tungsten trioxide (200 to 1030°), vanadium pentoxide (394 to 768°) also iron(II) sulfide (260 to 945°), and manganese tclluridc (230 to 600°C)... 

Following the pioneering work of Haruta and coworkers,90-92 numerous studies of Au as a catalyst have been reported. In their studies, Haruta and coworkers found that small Au clusters (<5 nm), highly dispersed on reducible metal-oxide supports, are quite active for a variety of catalytic... 

The major drawbacks to standard sol-gel synthesis include slow growth rate and the typically amorphous product, rather than defined crystals, which requires crystallization and post annealing steps. Growth rate and crystallization of the fabricated hybrid can be improved via solvothermal, reflux [224], sonication, and microwave [225] treatment. However, the air oxidation of CNTs (600 °C) and graphene (450 °C) may still be lower than MO crystallization temperature. Moreover, it has been shown that the MO coatings on CNTs can drastically affect their thermal oxidation, particularly with easily reducible metal oxides (e.g. TiOz = 520 °C, Bi203 = 330 °C) [180]. It appears that metal oxides can catalyze the oxidation of CNTs via a Mars van Krevelen mechanism, limiting the maximum temperature of their synthesis as well as applications (i.e. catalysis, fuel cells). 

Various in situ methods require post-treatments to induce crystallization or phase transformation. In some cases, however, the required temperatures for these treatments may be close to or even higher than those for the thermal oxidation of the nanocarbons themselves. Furthermore, it has been shown that the oxidation temperature of CNTs can be drastically reduced to as low as 330 °C, when coated with reducible metal oxides such as Bi203 [180], This process is thought to occur via a Mars van Krev-elen mechanism and may severely reduce the potential operating temperatures for various applications such as fuel cells. 

Metal oxide Reduced metal oxide + O2 (endothermic) (2.3.6)... 

Reduced metal oxide + 2H2O metal oxide + 2H2 (2.3.7)... 

Lithium hydride is a strong reducing agent and would, therefore, react with compounds that contain oxygen. Even many highly stable oxides of metals and nonmetals can be reduced. It reduces metal oxides to metals and carbon dioxide to carbon ... 

Lithium nitride reduces metal oxides and many metal chlorides to metallic state. It reduces copper(I) chloride to copper. Most of these reactions are exothermic. 

Sodium hydride is a powerful reducing agent. It reduces metal oxides, metal chlorides, and a number of oxidizible substances. Its reactions with water can proceed with explosive violence ... 

The most powerful reductants for the oxides shown in Fig. 17.9 are aluminum, magnesium, and calcium. Scrap aluminum can be used in the thermite reaction to reduce metal oxides, for example, C Os ... 

Droplets entering the flame evaporate then the remaining solid vaporizes and decomposes into atoms. Many elements form oxides and hydroxides in the outer cone. Molecules do not have the same spectra as atoms, so the atomic signal is lowered. Molecules also emit broad radiation that must be subtracted from the sharp atomic signals. If the flame is relatively rich in fuel (a rich flame), excess carbon tends to reduce metal oxides and hydroxides and thereby increases sensitivity. A lean flame, with excess oxidant, is hotter. Different elements require either rich or lean flames for best analysis. The height in the flame at which maximum atomic absorption or emission is observed depends on the element being measured and the flow rates of sample, fuel, and oxidizer.6... 

A redox mechanism for oxidation catalysis was proposed by Mars and van Krevelen (34) for the oxidation of aromatics over V205. This mechanism introduced the concept that lattice oxygen of a reducible metal oxide could serve as a useful oxidizing agent for hydrocarbons. Moreover, it formed the basis for the early work at SOHIO which led to the development of the bismuth molybdate catalyst. Since that time there have been many reports which support the redox concept. 

There are four important conditions for Au to be active as a catalyst in oxidation (1) strong junction with reducible metal oxides, (2) H20, (3) OH- and (4) the size of Au particles and films. At least two conditions should be fulfilled for Au to exhibit high catalytic activity. Catalysis by Au is often promoted by water and alkaline but destroyed by acids, which presents an interesting research topic in catalysis science. 

Carbon, a non-metal, is included in Table 10.1 (p. 150) just below aluminium. It is able to reduce metal oxides below it in the series. 

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