Metal antimonates

The multifunctionality is achieved through either the combination of two different compounds (phase-cooperation) or the presence of different elements inside a single crystalline structure. In antimonates-based systems, cooperation between the metal antimonate (having a rutile crystalline structure), employed for propane oxidative dehydrogenation and propene activation, and the dispersed antimony oxide, active in allylic ammoxidation, is made more efficient through the dispersion of the latter compound over the former. In metal molybdates, one single crystalline structure contains both the element active in the oxidative dehydrogenation of the hydrocarbon (vanadium) and those active in the transformation of the olefin and in the allylic insertion of the N H2 species (tellurium and molybdenum). 

Several papers have been published dealing with the study of metal antimonates having the rutile structure. In particular, V/Sb/O and Fe/Sb/0 systems have been the subject of many investigations, aimed at understanding the nature of these mixed oxides, and at the identification of the active species. 

Indeed, the preparation of a truly stoichiometric metal antimonate, MSb04 (M = metal), is a difficult task. The method of preparation employed affects the nature of the catalysts prepared, but in general non-stoichiometry is a particular feature of these systems [47-50]. The most striking case is the V/Sb/O system, for which the composition Vo.92Sbo.92O4 (quasi-VSh04) has been reported for the catalyst with the V/Sb atomic ratio equal to 1/1 [49]. This cation-deficient structure, which has 0.04 cationic positions unoccupied per anion, contains Sb, while... 

Semenov and Smirnova [295] showed by the use of Pt Knudsen cells that the alkali metal antimonates, with the exception of LiSbOjfs), vaporize con-gruently according to the reaction... 

The impact of photoacid generator (PAG) stmcture has been largely ignored for 193-nm single layer resists due to the concentrated polymer-oriented work discussed above. Most published work to date has involved the use of triflic or metallic (antimonate or arsenate) photoacids. Many PAGs used in DUV (248 nm) resists are inefficient when formulated with (non-phenolic) polymers used in 193-nm resists, presumably due to the lack of the electron transfer sensitization pathway thought to be in use in phenolic systems (i.e., 248nm resists). 

Crude lead contains traces of a number of metals. The desilvering of lead is considered later under silver (Chapter 14). Other metallic impurities are removed by remelting under controlled conditions when arsenic and antimony form a scum of lead(II) arsenate and antimonate on the surface while copper forms an infusible alloy which also takes up any sulphur, and also appears on the surface. The removal of bismuth, a valuable by-product, from lead is accomplished by making the crude lead the anode in an electrolytic bath consisting of a solution of lead in fluorosilicic acid. Gelatin is added so that a smooth coherent deposit of lead is obtained on the pure lead cathode when the current is passed. The impurities here (i.e. all other metals) form a sludge in the electrolytic bath and are not deposited on the cathode. 

The niter and fresh caustic soda, required to maintain the fluidity of the salt bath in the reactor chamber, are added gradually. When the color of the saturated salts turns from a dark gray to white, the impurity metals are at their highest state of oxidation, and the lead content of the spent salts is very low. In a modification, the arsenic and tin are selectively removed as sodium arsenate and sodium stannate, followed by the removal of antimony as sodium antimonate. 

Wet Process. The sodium arsenate and stannate slag are treated by a leach and precipitation process to produce calcium arsenate, calcium stannate, and a sodium hydroxide solution for recycle. The sodium antimonate filtercake containing selenium, tellurium, and indium is treated in a special metals refinery to recover indium and tellurium. 

Antimony trioxide is insoluble in organic solvents and only very slightly soluble in water. The compound does form a number of hydrates of indefinite composition which are related to the hypothetical antimonic(III) acid (antimonous acid). In acidic solution antimony trioxide dissolves to form a complex series of polyantimonic(III) acids freshly precipitated antimony trioxide dissolves in strongly basic solutions with the formation of the antimonate ion [29872-00-2] Sb(OH) , as well as more complex species. Addition of suitable metal ions to these solutions permits formation of salts. Other derivatives are made by heating antimony trioxide with appropriate metal oxides or carbonates. 

The roaster product is then charged to the Dorn furnace where it is melted and the resulting metal is fire-refined to eliminate the arsenates, selenates, antimonates, teUurates, and residual copper. 

In addition to the various complex fluoro-antimonate(in) salts M SbF 4 and M SbFs mentioned above, the alkali metals form complexes of stoichiometry M ShiF , M SbyFio and M Sb4Fj3, i.e. [SbFj (SbF ),) (n = 1, 2, 3)... 

Chlor-. of or combined with chlorine, chloro (as Chlorbenzoeadure, chlorobenzoic acid), chloride of (as Chlorzink, zinc chloride), chlorahnlich, a. like chlorine, chlorinous. Chlor-alaun, m. chloralum, -alkalien, n.pl. alkali-metal chlorides, -allyl, n, allyl chloride, -aluminium, n. aluminum chloride, -ammon, m., -ammonium, n. ammonium chloride, -amyl, n, amyl chloride, -antimon, n, antimony chloride, -arsenlk, n. chloride of arsenic, -arsenikldsung, /, (Pkarm.) solution of arsenious add, hydrochloric solution of arsenic, -arsinkampfstoff, m. chlorodi-phenylarsine, adamsite, chlorartig, a. like chlorine, chlorinous,... 

Roh-alkohol, m. crude (or raw) alcohoL -analyse, /. rough or approximate analysis, -antimon, n. crude antimony, -arbeit, /, (Metal.) ore smelting, -asbest, m. crude asbestos. -aufbereitung, /. preliminary preparation, -benzol, n. crude benzene, benzol (or benzole), -blei, n. crude lead, -blende, /. (Mining) crude blende, -block,... 

SpiessglanZ kermes, m. kermesite kermes mineral, -kbnig, m. regulus of antimony, -leber,/. livex of antimony, hepar antimonii. -metall, n. antimony, -mittel, n. antimonial remedy, -mohr, m. aethiops antimonialis (old pharmaceutical preparation of mercury and antimony sulfides). -ocker, m, antimony ocher, -oxyd,n. antimon> trioxide. -safran,... 

Another industrially important reaction of propylene, related to the one above, is its partial oxidation in the presence of ammonia, resulting in acrylonitrile, H2C=CHCN. This ammoxidation reaction is also catalyzed by mixed metal oxide catalysts, such as bismuth-molybdate or iron antimonate, to which a large number of promoters is added (Fig. 9.19). Being strongly exothermic, ammoxidation is carried out in a fluidized-bed reactor to enable sufficient heat transfer and temperature control (400-500 °C). 

As mentioned above, the conventional diazonium salts have good optical properties as CEL dyes and negative working sensitizers for the two-layer resist system. However, almost all diazonium salts are stabilized with metal-containing compounds such as zinc chloride, tetrafluoroborate, hexafluoro-antimonate, hexafluoroarsenate, or hexafluorophosphate, which may not be desirable in semiconductor fabrication because of potential device contamination. To alleviate the potential problem, new metal-free materials have been sought for. 

Treatment with NaOH solution produces sodium pyroantimonate, Na(H20)e [Sb(OH)6]2 [10049-22-6] and sodium hexahydroxo antimonate(V), Na[Sb(OH)6] [12339-41-2]. Heating with metal oxides and carbonates produces various polyantimonate(V) derivatives. 

Preparation.—1. By igniting antimonic oxide, or the white solid produced by the action of nitric acid upon metallic anti> mony.— ... 

Acrolein and Acrylic Acid. Acrolein and acrylic acid are manufactured by the direct catalytic air oxidation of propylene. In a related process called ammoxida-tion, heterogeneous oxidation of propylene by oxygen in the presence of ammonia yields acrylonitrile (see Section 9.5.3). Similar catalysts based mainly on metal oxides of Mo and Sb are used in all three transformations. A wide array of single-phase systems such as bismuth molybdate or uranyl antimonate and multicomponent catalysts, such as iron oxide-antimony oxide or bismuth oxide-molybdenum oxide with other metal ions (Ce, Co, Ni), may be employed.939 The first commercial process to produce acrolein through the oxidation of propylene, however, was developed by Shell applying cuprous oxide on Si-C catalyst in the presence of I2 promoter. 

During the history of a half century from the first discovery of the reaction (/) and 35 years after the industrialization (2-4), these catalytic reactions, so-called allylic oxidations of lower olefins (Table I), have been improved year by year. Drastic changes have been introduced to the catalyst composition and preparation as well as to the reaction process. As a result, the total yield of acrylic acid from propylene reaches more than 90% under industrial conditions and the single pass yield of acrylonitrile also exceeds 80% in the commercial plants. The practical catalysts employed in the commercial plants consist of complicated multicomponent metal oxide systems including bismuth molybdate or iron antimonate as the main component. These modern catalyst systems show much higher activity and selectivity... 

---