Molybdenum phosphate system

The closed-shell nature of aluminosilicates renders them ineffective for certain reactions favoured by transition (d-block) elements. Haushalter has made efforts to prepare stable shape-selective microporous solids involving molybdenum phosphates [15]. These solids are prepared hydrothermally in aqueous HjPO in the presence of cationic templates along with anionic octahedral-tetrahedral frameworks containing Mo in oxidation state less than 5+ and possessing Mo-Mo bonds. Some of these contain around 40 vol% accessible internal void space. There is rich chemistry in these systems and there is considerable potential for applications. Based on this approach one may indeed discover novel microporous and catalytic oxide systems. Several open-framework metal phosphates [16] and carboxylates [17] with different connectivities have been prepared by hydrothermal synthesis. 

Basic zinc molybdenum phosphate hydrate. Zinc molybdate is added to basic zinc phosphate hydrate so it can be used with water-soluble systems. 

Eberlein and Kattner [194] described an automated method for the determination of orthophosphate and total dissolved phosphorus in the marine environment. Separate aliquots of filtered seawater samples were used for the determination orthophosphate and total dissolved phosphorus in the concentration range 0.01-5 xg/l phosphorus. The digestion mixture for total dissolved phosphorus consisted of sodium hydroxide (1.5 g), potassium peroxidisulfate (5 g) and boric acid (3 g) dissolved in doubly distilled water (100 ml). Seawater samples (50 ml) were mixed with the digestion reagent, heated under pressure at 115-120 °C for 2 h, cooled, and stored before determination in the autoanalyser system. For total phosphorus, extra ascorbic acid was added to the aerosol water of the autoanalyser manifold before the reagents used for the molybdenum blue reaction were added. For measurement of orthophosphate, a phosphate working reagent composed of sulfuric acid, ammonium molyb-... 

The vendor claims that the following metals have been successfully treated to parts per biUion (ppb) and detection limit levels aluminum, arsenic, cadmium, chromium, cobalt, copper, iron, lead, manganese, mercury, molybdenum, nickel, selenium, silver, tin, uranium, vanadium, and zinc. The system is also able to remove ammonia, nitrates, phosphates, potassium, fluorides, and sodium. Studies have also been performed using Aqua-Fix to remove radionuchdes such as uranium from waste streams. 

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. 

Ingle and Crouch described a diflerential kinetic method for silicate and phosphate based on the faster rate of formation of heteropoly molybdenum blue from the yellow heteropoly acids in the presence of phosphate than in the presence of silicate. They found that silicon in the range of 1 to 10 ppm could be determined with 3% accuracy in the presence of 10 ppm of phosphorus, and phosphorus in the range of 1 to 10 ppm with 1% accuracy in the presence of 50 ppm of silicon. This system was also automated, with the analyses of mixtures being performed in less than 5 min. 

Many heterogeneous catalytic systems have been developed and applied to ammoxidation reactions. Vanadium-containing oxides are preferred as supported, bulk, or multicomponent catalysts for the ammoxidation of aromatic or heteroaromatic compounds. Favored supports are titanium oxide (anatase) [18,19], zirconium oxide [20,21], tin oxide [22], or mixed supports such as titanium-tin oxide [23]. Catalytic systems used as bulk materials include vanadium-phosphorus oxides [24], crystalline vanadium phosphates [25], and vanadium oxide combined with antimony oxide [26] or molybdenum oxide [27]. Other important catalysts include multicomponent systems such as KNiCoFeBiPMoO c on silica... 

The carrier stream contains molybdate and ascorbic acid. Since a mixture of these two components is not stable, they are mixed in the system ahead of the sample injection valve. Phosphate forms with molybdate a heteropolyacid in which molybdenum can be reduced from oxidation state 6 to 5 with ascorbic acid forming an intensely blue complex which can be measured spectrophotometrically at 660 nm. Although the first reaction is fast, the second one is relatively slow however, the precise timing of the FIA system ensures that the same fraction of the heteropolyacid is reduced. Thus the recorded absorbance peak is proportional to the concentration of phosphate present in the sample (Fig. 6.3 ). 

Skclch a flow injection system that could he used for the determination ot phosphate in a river water sample by means of the molybdenum blue reaction (phosphate -t molybdate i ascorbic acid in acid solution give phosphoniolybdonum blue, which absorbs at 66() nm),... 

Molybdenum SmokejFlame Suppressants. Product sheets of Climax Molybdenum Co., 1985 Siegel, D. Flame-retardant PP for engineering applications. Plast. Eng. 40, No. 8, 25 0984) Montaudo, G., Scamporrino, E. and Vitalini, D. Intumescent flame retardants for polymers. II. The polypropylene — ammonium phosphate — polyurea system. J. Polym. Sci. Polym. Chem. Ed 21, 3361 (1983)... 

Most kinetic determinations of anions involve the iodide ion, which exhibits a strong catalytic effect on the reaction between cerium(IV) and arsenic(III) and a few others as a result of the redox properties of the I2/ I couple. Other anions that can be determined using their intrinsic catalytic effect include sulfur-containing species such as sulfite, sulfide, and thiosulfate, which are quantified by means of the iodine/sodium azide system, and phosphates, which are measured through their effect on the formation of molybdenum blue. Table 5 gives illustrative examples of determinations for these anions and a few others. 

At cellular level, the overall reduction process may be represented as (11.72), where the nitroge-nase system is an enzyme complex which includes phosphate energy carriers ATP and NADPH and three proteins. Two of these proteins are metalloenzymes, one of which contains iron, and the other both iron and molybdenum. The third protein, ferredoxin, contains iron and sulphur and acts as an electron provider through NADPH. 

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