Metal oxides, catalysts Molybdenum

The first-stage catalysts for the oxidation to methacrolein are based on complex mixed metal oxides of molybdenum, bismuth, and iron, often with the addition of cobalt, nickel, antimony, tungsten, and an alkaU metal. Process optimization continues to be in the form of incremental improvements in catalyst yield and lifetime. Typically, a dilute stream, 5—10% of isobutylene tert-huty alcohol) in steam (10%) and air, is passed over the catalyst at 300—420°C. Conversion is often nearly quantitative, with selectivities to methacrolein ranging from 85% to better than 95% (114—118). Often there is accompanying selectivity to methacrylic acid of an additional 2—5%. A patent by Mitsui Toatsu Chemicals reports selectivity to methacrolein of better than 97% at conversions of 98.7% for a yield of methacrolein of nearly 96% (119). 

MAA and MMA may also be prepared via the ammoxidation of isobutylene to give meth acrylonitrile as the key intermediate. A mixture of isobutjiene, ammonia, and air are passed over a complex mixed metal oxide catalyst at elevated temperatures to give a 70—80% yield of methacrylonitrile. Suitable catalysts often include mixtures of molybdenum, bismuth, iron, and antimony, in addition to a noble metal (131—133). The meth acrylonitrile formed may then be hydrolyzed to methacrjiamide by treatment with one equivalent of sulfuric acid. The methacrjiamide can be esterified to MMA or hydrolyzed to MAA under conditions similar to those employed in the ACH process. The relatively modest yields obtainable in the ammoxidation reaction and the generation of a considerable acid waste stream combine to make this process economically less desirable than the ACH or C-4 oxidation to methacrolein processes. 

Catalytic alkylation of aniline with diethyl ether, in the presence of mixed metal oxide catalysts, preferably titanium dioxide in combination with molybdenum oxide and/or ferric oxide, gives 63% V/-alkylation and 12% ring alkylation (14). 

The high-density polyethylene is linear and can be manufactured by (i) coordination polymerisation of monomer by triethyl aluminium and tritanium chloride, (ii) polymerisation with supported Metal Oxide Catalysts. Such as chromium or molybdenum oxides supported over alumina-silica bases. 

The commercial process has always been to react methanol and air in the presence of a catalyst. Recent processes have switched from metal to metal oxide catalysts, especially iron oxide and molybdenum oxide. 

The newest and most commercially successful process involves vapor phase oxidation of propylene to AA followed by esterification to the acrylate of your choice. Chemical grade propylene (90—95% purity) is premixed with steam and oxygen and then reacted at 650—700°F and 60—70 psi over a molybdate-cobait or nickel metal oxide catalyst on a silica support to give acrolein (CH2=CH-CHO), an intermediate oxidation product on the way to AA. Other catalysts based on cobalt-molybdenum vanadium oxides are sometimes used for the acrolein oxidation step. 

One of the key discoveries during the first Raman experiments with cells that allowed control of the sample environment was a demonstration of the influence of moisture on the spectra of some catalysts. For example, supported metal oxide catalysts exhibit different Raman spectra depending on the loading of the metal oxide, such as molybdenum oxide. When the Raman spectra were recorded under ambient conditions, the spectra of the catalysts with low molybdenum loadings indicated the presence of monomolybdates, as characterized by the prominent band at about 900 cm-1. In contrast, polymolybdates, indicated by Raman bands between 930 and 960 cm-1, were detected at intermediate loadings, and crystalline M0O3 nanoparticles were found in materials with high... 

Some of the oxides of vanadium and molybdenum catalyze the selective oxidation of hydrocarbons to produce valuable chemical intermediates. In a reaction path proposed by Mars and van Krevelen (see Section 10.5), the hydrocarbon first reduces the surface of the metal oxide catalyst by reaction with lattice oxygen atoms. The resulting surface vacancies are subsequently re-oxidized by gaseous O2. The elementary steps of this process are shown below. Electrons are added to the sequence to illustrate the redox nature of this reaction. 

The most active catalyst is chromium oxide [7]. Silica (Si02) or aluminosilicates (mixed Si02/Al203) are used as the support material. The support is sometimes modified with titania (Ti02). The chromium oxide (Cr Os) catalyst was originally developed by Phillips Petroleum Company and is referred to as Phillips catalyst. Other metal oxide catalysts were developed primarily at Standard Oil of Indiana, the best known among them being the molybdenum oxide (Mo Os) catalyst. 

Some metal oxide catalysts are activated by thermal reduction with hydrogen or carbon monoxide. For example, the catalytic activity of molybdenum oxide and tungsten oxide for the metathesis reaction of olefins is very much enhanced by their slight reduction (1). The catalytic activity for butene isomerization and ethene oligomerization appears on niobium oxide by its... 

Although little experimental data is available, numerous patents have been issued for the vapor phase catalytic oxidation of various other derivatives containing the benzene nucleus, as well as heterocyclic compounds Thus, fluorene (diphenyl methane) is oxidized to fluorenone with air in the presence of a catalyst containing iron vanadate or other suitable metal salt of the fifth or sixth group of the periodic system at a temperature of 360° to 400°.1,2 Maleic acid and anhydride are formed by the catalytic oxidation of compounds of the furan series, such as furan, furfural alcohol, furfural, methyl furfural, hydroxymethylfurfural, pyromucic acid or mixtures, with air over catalysts of molybdenum, vanadium, or other metals.133 Dimethyl benzaldehyde is formed by oxidizing pseudocumene with air at 550° C. in the presence of a tungsten oxide catalyst. Molybdenum, vanadium, or tantalum oxide catalysts may also be used to form aromatic aldehydes from o-, m-, or p-xylenes, mesitylene, p-cymene, or o-chlorotoluene by air oxidation. Times of contact of 0.3 to 0.4 seconds... 

Propane Dehydrogenation over Supported Molybdenum Catalysts. The combined energy-dispersive (ED)-XAFS, UV-Vis, and Raman represents a powerful device that couples three spectroscopic techniques in one reactor, which probes the same part of a metal oxide catalyst under true reaction conditions and is capable of delivering subsecond time resolution. A scheme of the setup is given in Figure 32. 

Monolayer supported metal oxide catalysts possess a two-dimensional overlayer of an active metal oxide that is molecularly dispersed over a high surface area support. Usually, all the metal atoms deposited onto the oxide support are considered as the number of surface active sites. However, the application of methanol chemisorption as surface intermediate methoxy species on monolayer supported molybdenum. 

Briand, L.E., Earneth, W.E., and Wachs, I.E. Quantitative determination of the number of active sites and turnover frequencies for methanol oxidation over metal oxide catalysts. I. Fundamentals of the methanol chemisorption technique and application to monolayer supported molybdenum oxide catalysts. Catal Today 2000, 62, 219-229. 

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