Adsorption molybdenum

Molybdenum Cation exchange adsorption Molybdenum Cation exchange adsorption on Chelex-100... 

D.G. Kelly, M. Salmeron, and G.A. Somorjai, The adsorption and reactions of hydrocarbons on molybdenum single crystal surfaces when clean and in presence of coadsorbed sulfur or carbon, Surf. Sci. 175,465 (1986). 

Nitrogen adsorption/desorption isotherms on Zeolite and V-Mo-zeolite are very similar and close to a type I characteristic of microporous materials, although the V-Mo-catalysts show small hysterisis loop at higher partial pressures, which reveals some intergranular mesoporosity. Table 1 shows that BET surface area, microporous and porous volumes, decrease after the introduction of Molybdenum and vanadium in zeolite indicating a textural alteration probably because of pore blocking by vanadium or molybdenum species either dispersed in the channels or deposited at the outer surface of the zeolite. The effect is far less important for the catalysts issued from ZSM-5. 

Yoshimura et al. [193] carried out microdeterminations of phosphate by gel-phase colorimetry with molybdenum blue. In this method phosphate reacted with molybdate in acidic conditions to produce 12-phosphomolybdate. The blue species of phosphomolybdate were reduced by ascorbic acid in the presence of antimonyl ions and adsorbed on to Sephadex G-25 gel beads. Attenuation at 836 and 416 nm (adsorption maximum and minimum wavelengths) was measured, and the difference was used to determine trace levels of phosphate. The effect of nitrate, sulfate, silicic acid, arsenate, aluminium, titanium, iron, manganese, copper, and humic acid on the determination were examined. 

Van den Berg [510] carried out direct determinations of molybdenum in seawater by adsorption voltammetry. The method is based on complex formation of molybdenum (VI) with 8-hydroxyquinoline (oxine) on a hanging mercury drop electrode. The reduction current of adsorbed complexions was measured by differential pulse adsorption voltammetry. The effects of variation of pH and oxine concentration and of the adsorption potential were examined. The method was accurate up to 300 nmol/1. The detection limit was 0.1 nmol/1. 

Various other techniques have been used to determine molybdenum, including adsorption voltammetry [510], electron-paramagnetic resonance spectrometry [512], and neutron activation analysis [513,514]. EPR spectrometry is carried out on the isoamyl alcohol soluble Mo(SCN)s complex and is capable of detecting 0.46 mg/1 molybdenum in seawater. Neutron activation is carried out on the /J-naphlhoin oxime [514] complex and the pyrrolidone dithiocar-bamate and diethyldithiocarbamate complex [513]. The neutron activation analysis method [514] was capable of determining down to 0.32 xg/l of molybdenum in seawater. 

Cathodic stripping voltammetry has been used [807] to determine lead, cadmium, copper, zinc, uranium, vanadium, molybdenum, nickel, and cobalt in water, with great sensitivity and specificity, allowing study of metal specia-tion directly in the unaltered sample. The technique used preconcentration of the metal at a higher oxidation state by adsorption of certain surface-active complexes, after which its concentration was determined by reduction. The reaction mechanisms, effect of variation of the adsorption potential, maximal adsorption capacity of the hanging mercury drop electrode, and possible interferences are discussed. 

Molybdenum Anion exchange resin adsorption (Biorad Agl-X8), elution Graphite furnace AAS <10p,g/l... 

Jyo A., Yamabe K., Egawa H., Behavior of methylenephosphonic acid chelating resin in adsorption and elution of molybdenum (VI), Sep. Sci. Technol. 31,1996,513-522. 

In an equilibrium study of the adsorption of molybdenum(VI) from aqueous solution onto activated carbon it has been found that the data are best explained in terms of an absorption model comprising the three species [HMo207] , Mo03(H20)3, and [HMo04] of which the dimer predominates by far (80). Computer treatment of potentiomet-ric (81) and spectrophotometric data (82) also indicated the possible existence of [HMo207] as a minor species in aqueous solution at low molybdenum concentration ( 2 X 104 Af). However, as its assumed stability region overlaps with several other polynuclear ions more direct evidence is needed before its existence can be accepted with certainty. 

Barling J, Anbar AD (2004) Molybdenum isotope fractionation during adsorption by manganese oxides. Earth Planet Sci Lett 217 315-329... 

Aveston J, Anacker EW, Johnson JS (1964) Hydrolysis of molybdenum (VI). Ultracentrifugation, acidity measurements, and Raman spectra of polymolybdates. Inorg Chem 3 735-746 Baes Jr. CF, Mesmer RE (1986) The Hydrolysis of Cations. Krieger Publishing Company, Melbourne, EL Barling J, Anbar AD (2004) Molybdenum isotope fractionation during adsorption by manganese oxides. Earth Planet Sci Lett, in press... 

The fact that surface structure, in particular steps and coordinatively unsaturated sites, has an influence on the state and reactivity of carbon monoxide is entirely in keeping with the empirical correlation (Fig. 6) between heat of adsorption, electron binding energies, and molecular state. Elegant studies by Mason, Somorjai, and their colleagues (32, 33) have established that with Pt(lll) surfaces, dissociation occurs at the step sites only, and once these are filled carbon monoxide is adsorbed molecularly (Fig. 7). The implications of the facile dissociation of carbon monoxide by such metals as iron, molybdenum, and tungsten for the conversion of carbon monoxide into hydrocarbons (the Fischer-Tropsch process) have been emphasized and discussed by a number of people (32,34). 

Type 2. An example of this is molybdenum (22), where interaction is clearly dissociative [0(1 s) value of 530.3 eV] at 295 K. Further exposure to water vapor results in molecular adsorption [0(ls) value 533 eV],... 

The anion vacancy sites have acid properties. As stated above, the catalytic activity and the hydrogenolytic behavior correlated with the acid properties of the catalyst, as well as the extent of reduction. Therefore, the adsorption of an aryl group will occur on the coordinatively unsaturated molybdenum sites generated during reduction. According to the reaction scheme for the hydrogenation of ethylene over a reduced MoOj-AljOj catalyst, ethylene becomes it-bonded at a second vacant ligand position of a coordinatively unsaturated Mo species and inserts to form the [Pg.267]

Finally, the active sites for the hydrogenolysis of asym DAM are Mo(IV) species that originated from the reduction of the octahedral Mo(VI) species. The adsorption of the aryl group occurs on the coordinatively unsaturated molybdenum sites, which have acidic properties this fact, in turn, leads to the reaction mechanism of the interaction between the active species and the substrates. 

The vapor adsorption of Mo(CO),5 in an EMT zeolite followed by nitration with ammonia under a thermal treatment proved to be an appropriate method to introduce molybdenum oxynitrides into the zeolite, preserving the zeolite crystallinity and giving a homogeneous distribution of the molybdenum species in the zeolite [35]. 

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