Ammonium heptamolybdate, aqueous solution

AMMONIUM compounds). Diammonium dimolybdate [27546-07-2] (NH 2 2 7 " ble commercially as the tetrahydrate and prepared from MoO and excess NH in aqueous solution at 100°C, has an infinite chain stmcture based on MoO octahedra. In aqueous solution the behavior of Mo(VI) is extremely pH-dependent (4). Above pH 7 molybdenum(VI) occurs as the tetrahedral oxyanion MoO , but below pH 7 a complex series of concentration-, temperature-, and pH-dependent equiUbria exist. The best known of these equiUbria lead to the formation of the heptamolybdate,... 

Mo/HZSM-5 catalysts (3 wt% Mo nominal loading) were prepared by incipient wetness impregnation with an aqueous solution of ammonium heptamolybdate (Merck), drying at 100°C, and calcination at 500°C for 6 h. 

Aqueous ammonium heptamolybdate (Alfa, (NH4)6Mo70244H20, 99.999%) solutions were prepared so that a metal loading of 6 wt % Mo would fill 80% of the available pore volume of the mesoporous synthetic clays. Following Mo impregnation and recalcination at 400°C for 5 hr, the pore volumes were measured again using an established LN2 physisorption... 

In the disproportionation (metathesis) of olefins, i.e. the reaction 2Ri-CH=CH-R2 a R1-CH=CH-R1 + R2-CH=CH-R2, a M0O3/ AI2O3 catalyst is often applied. Its preparation involves impregnation of Y-AI2O3 extrudates with an aqueous solution of ammonium heptamolybdate (AHM) or an ammoniacal solution of ammonium dimolybdate (ADM). 

Molybdenum may be added to a carbon support as heptamolybdate or, more often, as ammonium tetrathiomolybdate in aqueous solution. " Cobalt, as nitrate or acetate, may be added before or after The drying procedure is important for ensuring an even distribution of active components. ... 

It is well known that several transition metals form POM ions in solution, eventually incorporating other elements. Thus, acidification of aqueous solutions of ammonium or sodium molybdates yields different so-called iopolyanions. As an example, condensation reactions for molybdate in aqueous solution can be represented as a sequence of equilibria initiated by the formation of heptamolybdate ion ... 

Samples prepared by impregnation samples FMT-I and FMT-IS have been prepared by simultaneous or consecutive impregnation, respectively, of the titania support (Degussa P25, ca. 80% anatase, ca. 50 m. previously calcined at 500°C in air for 3 h) with aqueous solutions of ammonium heptamolybdate (AHM), and ferric nitrate (FeN. 

Mo/HZSM-5 (3Mo/HZ) was prepared as reported in [1, 2, 10], 3 wt.% Mo was introduced by impregnating HZSM-5 (Si02/Al203 mol ratio of 50) with a proper aqueous solution of ammonium heptamolybdate. It was dried at 383 K overnight, calcined in air at 773K for 6 h. The samples were pelletized, crushed and sieved before use. 

Reagents The carrier stream consists of a mixture of two solutions pumped at equal rates that is, (a) 0.005 M ammonium heptamolybdate (6.1793 g/liter) in 0.4 M nitric acid and (b) 0.7% (w/v) aqueous solution of ascorbic acid to which is added 1% (v/v) glycerine (to minimize precipitation of reaction products on the walls of the flow cell). 

Reagents Molybdate solution 0.0025 M ammonium heptamolybdate (3.0897 g/liter) in 0.2 M nitric acid. Ascorbic acid solution 0.25% (w/v) in 10% (v/v) aqueous glycerine solution. 

Stoichiometric iron molybdate (Fe2(Mo04) ) was prepared by coprec itation from aqueous solutions of iron (III) nitrate and ammonium heptamolybdate it was characterised BET analysis, XRD, atomic absorption spectrophotometiy, XPS, EDX, SEM, FTIR and Mdssbauer spectroscopy. Surfece acidity was characteri by NH3 TPD (temperature programmed desorption). 

---