Catalysts corundum

Vniios A process for catalytically pyrolyzing hydrocarbons to low molecular weight alkenes, similar to catalytic cracking but more efficient. The catalyst is either potassium vanadate on corundum or indium oxide on pumice. Developed by the All-Union Research Institute for Organic Synthesis, Moscow. 

Chromium(III) acetylacetonate, physical properties, 6 528t Chromium alloys, 6 468-523 Chromium alumina pink corundum, formula and DCMA number, 7 347t Chromium antimony titanium buff rutile, formula and DCMA number, 7 347t Chromium-based catalysts, 20 173 Chromium baths, 9 800-804... 

Figure 11.29 Temperature dependent conversion/selectivity diagrams A-D, varying synthesis conditions as indicated in the upper left corner (1% 1,3-butadiene in synthetic air, GHSV 3,000 to 12,000 h 1, ambient pressure, 150 to 350°C, catalyst volume, 2 mL, diluted with corundum (1/1 mL)).

Occurs in nature in abundance the principal forms are bauxites and lat-erites. The mineral corundum is used to produce precious gems, such as ruhy and sapphire. Activated aluminas are used extensively as adsorbents because of their affinity for water and other polar molecules and as catalysts because of their large surface area and appropriate pore sturcture. As adsorbents, they are used for drying gases and liquids and in adsorption chromatography. Catalytic properties may be attributed to the presence of surface active sites (primarily OFT, 02, and AF+ ions). Such catalytic applications include sulfur recovery from H2S (Clauss catalysis) dehydration of alcohols, isomerization of olefins and as a catalyst support in petroleum refining. 

Ziogas et al. [28] performed catalyst screening with this reactor with catalysts coatings, which were made of various base aluminas such as corundum, boehmite and y-alumina. Testing of Cu/Cr and Cu/Mn catalysts based on the different coatings for methanol steam reforming revealed differences in activity which were ascribed... 

A total of206 mg [119] of commercial Cu/Zn catalyst from SiidChemie (G-66MR) ground to the nanometer range was coated into the channel system at 5 pm thickness to promote the steam reforming reaction. A cobalt oxide catalyst was prepared by impregnating the corundum layer (see above) with cobalt nitrate and calcining at 350 °C for 2 h 434 mg [119] of the CoO catalyst were applied for the combustion reaction (see Section 2.5). 

In a reactor that is similar to a reformer, the reaction occurs in tubes that are heated externally to supply the endothermic heat of reaction129. Sintered corundum (a-Al203) tubes with an internal layer ( 15 microns thick) of platinum/ruthenium catalyst are used, hi some cases a platinum/aluminum catalyst may be used. To achieve adequate heat transfer, the tubes may be only % in diameter and 6V2 feet long. Selectivities of 90-91% for methane and 83-84% for ammonia are reached at 1200°C to 1300°C reaction temperatures. 

Iron oxide with a corundum-type structure, that is, aFe203, is a good catalyst for reactions such as the catalytic oxidation of S02 [53], Studies carried out on this reaction show that S02 adsorption is the rate-determining step it contributes electrons to the conduction band and the adsorption of 02 withdraws the conduction electrons from an oxygen vacancy [53],... 

Abbattista et al. (26) found that phosphorus addition prevents crystallization of the y-alumina phase and the transformation from y- to a-alumina in the system AI2O3 —AIPO4 (Fig. 23). More precisely, Morterra et al. (77) reported that phosphates do not affect the phase transition from low-temperature spinel alumina (y-alumina) to high-temperature spinel aluminas 8 and 6 phases) but delay the transition of 8 and 9 to a-alumina (corundum). Stanislaus et al 46) also reported that phosphorus significantly improves the thermal stabihty of the y-alumina phase in P/Al catalysts. However, the same authors found that the positive effect of phosphorus seems to be canceled in the presence of molybdenum due to the formation of aluminum molybdate. Thermal treatments of MoP/Al catalysts at temperatures >700°C result in a considerable reduction of SSA and mechanical strength. The presence of phosphorus does not prevent the reaction between the molybdenum oxo-species and alumina since the interaction between molybdates and phosphates is weak. The presence of nickel does not obviously affect the positive effect of phosphorus in terms of thermal stability 46). On the other hand, Hopkins and Meyers 78) reported that the thermal stability of commercial CoMo/Al and NiMo/Al catalysts is improved by the addition of phosphorus. 

The stable crystalline form is corundum (a-alumlna). Kappa-alumina is one of several structurally related, metastable forms. These occur In "active alumina" and are much studied (5) due to their Importance in adsorbents and catalysts. Llppens and Steggerda (5) summarized the classifications of metastable forms, their crystal structures and conditions of formation by dehydration. Okuralya et al. (6) recently published an extensive study on the formation and structural relations of 1C-AI2O3 and its precursors le -AlgOg and tohdlte. Kappa-alumina belongs to the "nearly anhydrous", high-temperature classification (5) based on its formation temperture of 900 to 1000 C (somewhat lower in vacuo). The Irreversible transition x+o is thermally activated at 1200 C (2, 5). Thermochemical studies cited In this table presume that the samples of x-Al Og were essentially anhydrous. 

Vapour-phase catalytic oxidation of isobutene was carried out at atmospheric pressure in a completely automated laboratory setup, including a fixed bed reactor (700 mm length, 10 mm inner diameter) with corundum as wall material. In order to ensure isothermicity, the heated section (200 mm in length) was divided into five independently heated zones and the catalyst bed was diluted with inert pellets (a-Al203). Inert pellets were placed above and below the catalyst bed to ensure a well-mixed feed stream, and to preheat the gas to the reaction temperature. Bi203 catalyst (Merck) was pressed into thin wafers and broken into small particles. Granules with a diameter of 0.8 -1.2 mm were used. 

The transformation into corundum occurs above 900°C, which temperature can be reached in a catalytic converter. Consequently it is necessary to stabilize the transition aluminas to high temperature (1250-1300°C) in order to improve the durability of the catalyst. 

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