Molybdenum based oxides

A novel selective oxidation catalyst ultrafme complex molybdenum based oxide particles ... 

Very recently, ultrafme metal oxides have attracted much research interests in terms of materials science and heterogeneous catalysis[10-12]. These new catalytic materials are expected to have unique catalytic properties because of their nano-scale particle sizes. In this work, a novel catalyst for selective oxidation of toluene to benzaldehyde, i.e. ultrafme complex molybdenum based oxide particles, has been developed. It has been found that the reactivity of lattice oxygen ions can be improved by decreasing the oxide particle size to nano-scale and that the ultrafme oxide particles exhibit unique catalytic properties for selective oxidation. Our results have revealed that the ultrafme complex oxide particles are potentially new catalytic materials for selective oxidation reactions. 

The most effective molybdenum-based oxide catalyst for propane ammoxidation is the Mo-V-Nb-Te-0 catalyst system discovered and patented by Mitsubishi Chemical Corp., Japan, U.S.A. (140). Under single-pass process conditions, acrylonitrile yields of up to 59% are reported, whereas under recycle process feed conditions, the acrylonitrile selectivity is 62% at 25% propane conversion (141). Although the latter results show that the catalyst operates effectively under recycle feed conditions, the catalyst system was originally disclosed for propane ammoxidation under single-pass process conditions. The catalyst was derived from the Mo-V-Nb-0 catalyst developed by Union Carbide Corp. for the selective oxidation of ethane to ethylene and acetic acid (142). The early work by Mitsubishi Chemical Corp. used tellurium as an additive to the Union Carbide catalyst. The yields of acrylonitrile from propane using this catalyst were around 25% with a selectivity to acrylonitrile of 44% (143). The catalyst was also tested for use in a regenerative process mode much like that developed earlier by Monsanto (144) (see above and Fig. 8). Operation under cyclic reduction/reoxidation conditions revealed that the performance of the catalyst improved when it was partially reduced in the reduction cycle of the process. Selectivity to acrylonitrile reached 67%, albeit with propane conversions of less than 10%, since activity in... 

Patents claiming specific catalysts and processes for thek use in each of the two reactions have been assigned to Japan Catalytic (45,47—49), Sohio (50), Toyo Soda (51), Rohm and Haas (52), Sumitomo (53), BASF (54), Mitsubishi Petrochemical (56,57), Celanese (55), and others. The catalysts used for these reactions remain based on bismuth molybdate for the first stage and molybdenum vanadium oxides for the second stage, but improvements in minor component composition and catalyst preparation have resulted in yields that can reach the 85—90% range and lifetimes of several years under optimum conditions. Since plants operate under more productive conditions than those optimum for yield and life, the economically most attractive yields and productive lifetimes maybe somewhat lower. 

The oxidative dehydration of isobutyric acid [79-31-2] to methacrylic acid is most often carried out over iron—phosphoms or molybdenum—phosphoms based catalysts similar to those used in the oxidation of methacrolein to methacrylic acid. Conversions in excess of 95% and selectivity to methacrylic acid of 75—85% have been attained, resulting in single-pass yields of nearly 80%. The use of cesium-, copper-, and vanadium-doped catalysts are reported to be beneficial (96), as is the use of cesium in conjunction with quinoline (97). Generally the iron—phosphoms catalysts require temperatures in the vicinity of 400°C, in contrast to the molybdenum-based catalysts that exhibit comparable reactivity at 300°C (98). 

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. 

Temperature Programmed Reaction. Examination of another redox system, propylene oxidation on M0O3, provides further insight. It is well accepted that propylene oxidation on molybdenum-based catalysts proceeds through formation of allylic intermediates. From isotopic studies it has been demonstrated that formation of the allylic intermediate is rate-determining (H/D effect), and that a symmetric allylic species is formed ( C labelling). 

Molybdenum-based catalysts are highly active initiators, however, monomers with functionalities with acid hydrogen, such as alcohols, acids, or thiols jeopardize the activity. In contrast, ruthenium-based systems exhibit a higher stability towards these functionalities (19). An example for a molybdenum-based catalyst is (20) MoOCl2(t-BuO)2, where t-BuO is the tert-butyl oxide radical. The complex can be prepared by reacting M0OCI4 with potassium tert-butoxide, i.e., the potassium salt of terf-butanol. 

Methacrolein and Methacrylic Acid. A two-stage technology, essentially the same as the propylene oxidation process for the manufacture of acrolein and acrylic acid, was developed to oxidize isobutylene to methacrolein and methacrylic acid 949-951 Two different molybdenum-based multicomponent catalysts are used. In a typical procedure949 isobutylene is reacted with excess steam and air (5 30 65) at about 350°C to produce a mixture of methacrolein and methacrylic acid with 80-85% selectivity at a conversion of 98%. In the second stage this reaction mixture is oxidized at slightly above 300°C to yield methacrylic acid (80% selectivity at >90% conversion). 

The selectivity of the acrylonitrile formation with respect to ammonia is very low (<10%) for the molybdenum-based catalysts (mainly due to N2 formation) but very high (100%) for the Sn—Sb—(Fe) catalyst. This is in agreement with the results of the separate oxidation of ammonia, which only in the case of Sn—Sb—(Fe) demands a temperature above that of the propene ammoxidation. 

Molybdenum-based anticorrosive pigments offer a nontoxic alternative to the zinc chromate pigments [5.120], They all have a neutral color (white) but the pure compounds are very expensive. To produce economically competitive pigments molybdate and phosphate pigments are combined, or molybdate compounds are applied to inorganic fillers (e.g., zinc oxide, alkaline-earth carbonates, or talc) [5.75], [5.121]—[5.123]. 

Before World War II, the use of molybdenum based catalysts was popular, with molybdenum oxide (and sometimes sulphide) used for a number of isomerization processes.4 These types of catalyst were less sensitive to sulphur in the feed but were phased out owing to inferior selectivity.5... 

Two processes are commonly used for the production of copper phthalocyanine the phthalic anhydride-urea process patented by ICI [33,34] and the I.G. Farben dinitrile process [48], Both can be carried out continuously or batchwise in a solvent or by melting the starting materials together (bake process). The type and amount of catalyst used are crucial for the yield. Especially effective as catalysts are molybdenum(iv) oxide and ammonium molybdate. Copper salts or copper powder is used as the copper source [35-37] use of copper(i) chloride results in a very smooth synthesis. Use of copper(i) chloride as starting material leads to the formation of small amounts of chloro CuPc. In the absence of base, especially in the bake process, up to 0.5 mol of chlorine can be introduced per mole of CuPc with CuCl, and up to 1 mol with CuCl2. 

Several procedures for this chemoselective oxidation utilize molybdenum-based catalysts, with either hydrogen peroxide or r-butyl hydroperoxide as the stoichiometric oxidant. These include ammonium molybdate in the presence of a ph e transfer reagent and hydrogen peroxide, which with pH control (potassium carbonate) will selectively oxidize a secondary alcohol in the presence of a primary alcohol without oxidizing alkenes. In addition hindered alcohols are oxidized in preference to less hindered ones (Scheme 18). 

Among the metal oxide pseudocapacitive materials the most representative are the crystalline ruthenium oxide Ru02 [24] and the amorphous hydrous ruthenium oxide Ru02 XH2O [27, 28], although other materials are under study, for example cobalt oxide [29] and vanadiun oxide [30] xerogels, molybdenum-based materials [31, 32], and Ti-V-W-O oxides [33]. 

Acrylic acid is a high volume chemical, continuous processing is used. Similar catalysts are used for both reactions, but the catalysts and conditions are sufficiently different that the reactions are conducted separately. Bismuth molybdate and molybdenum vanadium oxides typically are the bases for the catalysts in the first and second reactions, respectively. Effluent from the first reactor can go directly to the second reactor wilfrout processing. Fixed bed, shell-and-tube, solid-catalyst reactors are used for the gas-phase reaction. Reactors are cooled with circulating molten salts. Additional process information is presented as needed. 

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