Mixed metal oxides multicomponent

Although acrylonitrile manufacture from propylene and ammonia was first patented in 1949 (30), it was not until 1959, when Sohio developed a catalyst capable of producing acrylonitrile with high selectivity, that commercial manufacture from propylene became economically viable (1). Production improvements over the past 30 years have stemmed largely from development of several generations of increasingly more efficient catalysts. These catalysts are multicomponent mixed metal oxides mostly based on bismuth—molybdenum oxide. Other types of catalysts that have been used commercially are based on iron—antimony oxide, uranium—antimony oxide, and tellurium-molybdenum oxide. 

Al-Saeedi, J.N. and Guliants, V.V. (2002) High-throughput experimentation in multicomponent bulk mixed metal oxides Mo-V-Sb-Nb-O system for selective oxidation of propane to acrylic acid. Appl. Catal. A Gen, 237, 111. 

Light hydrocarbons consisting of oxygen or other heteroatoms are important intermediates in the chemical industry. Selective hydrocarbon oxidation of alkenes progressed dramatically with the discovery of bismuth molybdate mixed-metal-oxide catalysts because of their high selectivity and activity (>90%). These now form the basis of very important commercial multicomponent catalysts (which may contain mixed metal oxides) for the oxidation of propylene to acrolein and ammoxidation with ammonia to acrylonitrile and to propylene oxide. 

Acrylonitrile is currently the second largest outlet for propylene (after polypropylene). It is used as a monomer for synthetic fibers and acrylic plastics (thermoplastics and food packaging mainly), AS (acrylonitrile-styrene) resins, and ABS (aerylonitrile-butadiene-styrene) thermoplastics, as well as in the synthesis of acrylamide, adiponitrile, and nitrile elastomers. The manufacture of acrylonitrile is exclusively based on the one-step propylene ammoxidation process. Originally developed by Sohio, Standard Oil Company (now part of BP America), the conventional method used since 1957 employs a fluidized-bed reactor and multicomponent catalysts based on Mo-containing mixed-metal oxides. Over the years, the industrial... 

In principle it would seem reasonable that the bulk structure and surface properties of a solid would influence the catalytic performance. Verification of this view and an assessment of its importance may be more significant than first appears since it incorporates an implication that catalytic preparation should be designed to achieve the bulk structure and surface properties that give the optimized catalytic performance. Materials which have been shown to catalyze the conversion of propylene to acrolein have included metal oxides, mixed oxides, and more lately the multicomponent catalysts. A consideration of all these solids would require the assessment of numerous data and speculation. However, the mixed oxide catalysts have been associated with many of the more recent investigations of the course of catalytic oxidation, and these catalysts therefore seem to be worthy of detailed consideration. 

Meso-Macroporous Mixed Oxides Multicomponent oxides play a central role in chemical and petrochemical processing as catalysts and as supports for catalytically active species [145]. It is known that the catalytic efficiency of metal oxides can be improved by doping them with a metal or combining them with another metal oxide [145]. The strategy based on the self-formation phenomenon to fabricate the porous hierarchy demonstrated its simplicity and superiority in the synthesis of hierarchically meso-macroporous metal oxides with multiple compositions. 

Calcination or dead burning is used extensively to dehydrate cements (qv) and hygroscopic materials such as MgO, and to produce a less water sensitive product. Calcination is also used to decompose metal salts to base oxides and to produce multicomponent or mixed oxide powders for... 

The ample diversity of properties that these compounds exhibit, is derived from the fact that over 90% of the natural metallic elements of the periodic table are known to be stable in a perovskite oxide structure and also from the possibility of synthesis of multicomponent perovskites by partial substitution of cations in positions A and B giving rise to compounds of formula (AjfA i- )(ByB i-J,)03. This accounts for the variety of reactions in which they have been used as catalysts. Other interesting characteristics of perovskites are related to the stability of mixed oxidation states or unusual oxidation states in the structure. In this respect, the studies of Michel et al. (12) on a new metallic Cu2+-Cu3+ mixed-valence Ba-La-Cu oxide greatly favored the development of perovskites exhibiting superconductivity above liquid N2 temperature (13). In addition, these isomorphic compounds, because of their controllable physical and chemical properties, were used as model systems for basic research (14). 

It is also possible to precipitate multimetal ions to obtain multicomponent LDHs. For example, Morpurgo et al. synthesized several multication LDHs, such as CuZnCoAlCr- and CuZnCoCr-LDHs (192-194). This procedure suggests a general way to synthesize a number of LDHs as the precursors of mixed oxides with versatile functionalities, especially through incorporation of some rare earth metal cations (with radius from 0.085 to 0.100 nm), as has been done by Perez-Ramirez et al. (163,165). However, the overall ratio of divalent to trivalent cations should be kept in the range of 0.2-0.4. 

Acrylic acid has traditionally been used as the raw material for acrylic estos, polyacrylates, cross-linked polyacrylates, and copolymers. The global acrylic acid capacity was ca. 4.7 million tons in 2006, with an estimated average growth of 4%. Nowadays, acrylic acid is industrially obtained from a physically separated two-step process with propylene as the starting raw material. Firstly, propylene is selectively oxidized to acrolein at 300-350 C employing multicomponent catalysts based on metallic mixed oxides, i.e. MoBiO, FeSbO, or SnSbO. Then, the acrylic acid is obtained in a second step from acrolein oxidation at 200-260°C using multicomponent catalysts based on Mo-V-W mixed oxides. Thus, an overall acrylic acid yield of 85-90% is reached. 

Very different catalytic materials have been tested in the selective oxidation of propane, which includes vanadium phosphorous oxide (VPO) catalysts, industrially applied for w-butane oxidation to maleic anhydride. The other catalysts systems include Keggin structure heteropolyoxometalUc compounds (HPCs) and multicomponent mixed oxides (MMOs). These materials have different structure and properties, but have something in common they contain reducible metal 0x0 species. 

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