Promoters zinc oxide

This alcohol can be reacted with methanol in the presence of a catalyst to produce methyl-r-butyl ether. Although it is currently cheaper to make Ao-butyl alcohol from Ao-butcne (Ao-butylene), it can be synthesized from syngas with alkali-promoted zinc oxide catalysts at temperatures above 400°C (750°F). 

The first reactor (high-temperature shift) is loaded with high-temperature catalyst, generally chromium-promoted iron oxide, which operates at 623—673 K (Ledjeff-Hey, Roes, Wolters, 2000). The second reactor (low-temperature shift) is loaded with low-temperature catalyst of copper-promoted zinc oxide, which operates at 473 K (Ledjeff-Hey et al., 2000). 

The raw dust-free syngas from purification of coal and heavy hydrocarbons contains sulphur as COS and H2S (Table 1.18) according to the equilibrium (see Appendix 2). COS can be removed by a promoted zinc oxide [246]. 

Waddell did some work on the changes in the interfacial layers [41]. A wide range of surface-analytical tools were used Auger electron spectroscopy (AES), x-ray photoelectron spectroscopy (XPS), SEM, EDX, and particle indnced x-ray emission (PIXE), which indicated that silica use reduced the thickness of the interfacial film, and particularly promoted zinc oxide formation and lowered the amount of sulphide formed. 

The role of silica-only systems on adhesion has been studied using model compounds with squalene [59]. It was shown that the mechanism for increased adhesion to brass-coated wire-to-rubber was not just a simple improvement of the physical properties of the rubber, but that silica moderated the thickness and composition of the interfacial layer by a chemical interaction. SEM-EDX (scanning electron microscopy with energy dispersive analysis of X-rays), XPS, AES and PIXE (proton induced X-ray emission spectroscopy) revealed that silica affected the relative concentrations of compounds present in the interfacial layer, promoting zinc oxide formation in particular. 

The stmctural promoter zinc oxide, which in most cases is added to commercial catalysts for methanol synthesis, is very effective in reducing the sulfur poisoning by the removal of H2S from gas stream and the formation of zinc sulfide. The additive ZnO offers therefore a certain degree of protection against poisoning with sulfur compounds ... 

Zinc Ferrite and Tttanate Sorbents, 1324 Haldor Topsee Tin Oxide-Based Process, 1328 Z-Sorb Promoted Zinc Oxide-Based Process, 1329... 

Z-Soit Promoted Zinc Oxide-Based Process... 

Methanol is prepared by the interaction of carbon monoxide and hydrogen. In older plants in which a promoted zinc oxide catalyst is utilized, reaction conditions are 300-400°C and about 30 MPa (300 atmospheres). In newer plants a copper-based catalyst is employed this allows the use of milder conditions, namely 200-300°C and 5-10 MPa (50-100 atmospheres). The methanol is condensed out and unreacted gases, with fresh make-up gas, recycled to the converters. In the second stage, methanol is oxidized to formaldehyde. In one process a mixture of methanol vapour and air is passed over a catalyst of molybdenum oxide promoted with iron at 350-450°C. The exit gases are scrubbed with water and the formaldehyde is isolated as an aqueous solution. 

Promoter Zinc oxide Stearic acid N-990 (MT) black N-550 (FEE) black Paraffinic oil DTDM TMTD... 

When the operating temperature exceeds ca 93°C, the catalytic effects of metals become an important factor in promoting oil oxidation. Inhibitors that reduce this catalytic effect usually react with the surfaces of the metals to form protective coatings (see Metal surface treatments). Typical metal deactivators are the zinc dithiophosphates which also decompose hydroperoxides at temperatures above 93°C. Other metal deactivators include triazole and thiodiazole derivatives. Some copper salts intentionally put into lubricants counteract or reduce the catalytic effect of metals. 

This reaction is first conducted on a chromium-promoted iron oxide catalyst in the high temperature shift (HTS) reactor at about 370°C at the inlet. This catalyst is usually in the form of 6 x 6-mm or 9.5 x 9.5-mm tablets, SV about 4000 h . Converted gases are cooled outside of the HTS by producing steam or heating boiler feed water and are sent to the low temperature shift (LTS) converter at about 200—215°C to complete the water gas shift reaction. The LTS catalyst is a copper—zinc oxide catalyst supported on alumina. CO content of the effluent gas is usually 0.1—0.25% on a dry gas basis and has a 14°C approach to equihbrium, ie, an equihbrium temperature 14°C higher than actual, and SV about 4000 h . Operating at as low a temperature as possible is advantageous because of the more favorable equihbrium constants. The product gas from this section contains about 77% H2, 18% CO2, 0.30% CO, and 4.7% CH. ... 

Hydrogenation. Gas-phase catalytic hydrogenation of succinic anhydride yields y-butyrolactone [96-48-0] (GBL), tetrahydrofiiran [109-99-9] (THF), 1,4-butanediol (BDO), or a mixture of these products, depending on the experimental conditions. Catalysts mentioned in the Hterature include copper chromites with various additives (72), copper—zinc oxides with promoters (73—75), and mthenium (76). The same products are obtained by hquid-phase hydrogenation catalysts used include Pd with various modifiers on various carriers (77—80), Ru on C (81) or Ru complexes (82,83), Rh on C (79), Cu—Co—Mn oxides (84), Co—Ni—Re oxides (85), Cu—Ti oxides (86), Ca—Mo—Ni on diatomaceous earth (87), and Mo—Ba—Re oxides (88). Chemical reduction of succinic anhydride to GBL or THF can be performed with 2-propanol in the presence of Zr02 catalyst (89,90). 

In paints, zinc oxide serves as a mildewstat and acid buffer as well as a pigment. The oxide also is a starting material for many zinc chemicals. The oxide supphes zinc in animal feeds and is a fertilizer supplement used in zinc-deficient soils. Its chemical action in cosmetics (qv) and dmgs is varied and complex but, based upon its fungicidal activity, it promotes wound healing. It is also essential in nutrition. Zinc oxide is used to prepare dental cements in combination with eugenol and phosphoric and poly(acrylic acid)s (48) (see Dental materials). 

High pressure processes P > 150 atm) are catalyzed by copper chromite catalysts. The most widely used process, however, is the low pressure methanol process that is conducted at 503—523 K, 5—10 MPa (50—100 atm), space velocities of 20, 000-60,000 h , and H2-to-CO ratios of 3. The reaction is catalyzed by a copper—zinc oxide catalyst using promoters such as alumina (31,32). This catalyst is more easily poisoned than the older copper chromite catalysts and requites the use of sulfiir-free synthesis gas. 

Metal oxides. Zinc oxide is the most effective metal oxide. The zinc oxide should have a low lead content. Zinc oxide has three main functions (a) promote cure (b) improves ageing, heat and weathering resistance (c) acid acceptor. In general, 2-5 phr zinc oxide is added in latex formulations. 

Clean metallic aluminum is extremely reactive. Even exposure to air at ordinary temperatures is sufficient to promote immediate oxidation. This reactivity is self-inhibiting, however, which determines the general corrosion behavior of aluminum and its alloys due to the formation of a thin, inert, adherent oxide film. In view of the great importance of the surface film, it can be thickened by anodizing in a bath of 15% sulfuric acid (H2SO4) solution or by cladding with a thin layer of an aluminum alloy containing 1 % zinc. 

The rate of reaction is controlled by the diffusion process, as the sulfide ion must first diffuse to the surface of the zinc oxide to react. High temperature (>250°F) increases the diffusion rate and is normally used to promote the reaction rate. 

In some parts of the world, as in Russia, fermented alcohol can serve as a cheap source for hutadiene. The reaction occurs in the vapor phase under normal or reduced pressures over a zinc oxide/alumina or magnesia catalyst promoted with chromium or cohalt. Acetaldehyde has been suggested as an intermediate two moles of acetaldehyde condense and form crotonaldehyde, which reacts with ethyl alcohol to give butadiene and acetaldehyde. 

Magnesium oxide is always blended with the zinc oxide prior to ignition. Magnesium oxide promotes densification of the zinc oxide, preserves its whiteness and renders the sintered powder easier to pulverize (Crowell, 1929). The sintered mixed oxide has been shown to contain zinc oxide and a solid solution of zinc oxide in magnesium oxide (Zhuravlev, Volfson Sheveleva, 1950). Specific surface area is reduced compared with that of pure zinc oxide and cements prepared from the mixed oxides are stronger (Crowell, 1929 Zhuravlev, Volfson Sheveleva, 1950). 

Eugenol is a very weak acid (p = 10-4) and will not react with zinc oxide in the absence of promoters. These reaction promoters include water, acetic acid and zinc acetate. 

Incorporation of promoters can occur via two distinct mechanisms. A local pH drop at the leach front caused by the aluminum dissolution can cause a solvated promoter to deposit via a shift in the solubility equilibrium. Zincate shows this behavior, depositing as zinc oxide as the pH drops at the leach... 

Promoter deposition through different mechanisms can account for different catalyst properties. In particular, chromate depositing as chromia does not easily redissolve but, zinc oxide does redissolve once the leach front passes and the pH returns to the bulk level of the lixiviant. Therefore, chromate can provide a more stable catalyst structure against aging, as observed in the skeletal copper system. Of course, promoter involvement in catalyst activity as well as structural promotion must be considered in the selection of promoters. This complexity once again highlights the dependence of the catalytic activity of these materials on the preparation conditions. 

Pure decarbonylation typically employs noble metal catalysts. Carbon supported palladium, in particular, is highly elfective for furan and CO formation.Typically, alkali carbonates are added as promoters for the palladium catalyst.The decarbonylation reaction can be carried out at reflux conditions in pure furfural (165 °C), which achieves continuous removal of CO and furan from the reactor. However, a continuous flow system at 159-162 °C gave the highest activity of 36 kg furan per gram of palladium with potassium carbonate added as promoter. In oxidative decarbonylation, gaseous furfural and steam is passed over a catalyst at high temperatures (300 00 °C). Typical catalysts are zinc-iron chromite or zinc-manganese chromite catalyst and furfural can be obtained in yields of... 

In 1802 he became a Privatdozent in the faculty of medicine at Gottingen, and was rapidly promoted until in 1810 he became a full professor (Professor ordinarius). In the German universities, as in certain American ones, professors frequently hold government offices. Dr. Stromeyer was the inspector-general of all the apothecaries of Hanover. On an inspection trip to Hildesheim in the autumn of 1817 he noticed that a certain preparation which, according to the Hanoverian Pharmacopoeia, ought to have contained zinc oxide, contained zinc carbonate instead. The events which followed were described by Dr. Stromeyer in his letter to Dr. J. S. C. Schweigger written on April 26, 1818 ... 

In addition to dicumyl peroxide (DCP), in two different batches zinc oxide (ZnO) or a conventional organic accelerator (ZDMC) were used. Figure 34 depicts the corresponding XRD pattern. In both cases, the peak positions are almost the same as that of the pure peroxide-cured vulcanizates. However, the intensity of the XRD pattern was significantly reduced in the case of ZDMC, and there is only a little effect of ZnO. Obviously, the sulfur-containing zinc salt influences and promotes dispersion and reorientation of the layered... 

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