Reductive co-precipitation

Reductive co-precipitation of noble metals with a suitable collector (Te, Se, As, Hg, and Cu) may provide uncertainty when examining complex environmental samples as a result of difficulties with complete separation of high amounts of common metals, which can partially pass into the precipitate, and possible loss of PGMs. Recovery of Pt from soil samples was reported to be 55-87 % after its separation by co-precipitation with Te [88]. Long analysis time is a disadvantage of such a procedure. 

Alsenz, H., Zereini, F., Wiseman, C.L.S., Puttmann, W. Analysis of palladium concentrations in airborne particulate matter with reductive co-precipitation. He collision gas, and ID-ICP-Q-MS. Anal. Bioanal. Chem. 395, 1919-1927 (2009)... 

Analysis of Palladium Concentrations in Airborne Particulate Matter with Reductive Co-Precipitation,... 

The results show that Pd can be effectively and accurately measured in airborne PM using Hg reductive co-precipitation to isolate and pre-concentrate samples and isotope dilution ICP-MS with He as a colhsion gas. The method proved to be effective for the determination of Pd in airborne PM for background samples at very low concentrations in the pg/m range. The procedural blank was determined to be 0.01 pg Pd/m, while the limit of determination (LOD) was calculated to be... 

Alsenz H, Zereini F, Wiseman C, Piittmann W (2009) Determination of palladium in airborne particulate matter using isotope dilution-quadrupole-inductively coupled plasma-mass spectrometry (ID-Q-ICP-MS) with helium as a collision gas after reductive co-precipitation with mercury. Anal Bioanal Chem 395 1919-1927 Alt F, Bambauer A, Hoppstock K, Mergler B, Tdlg G (1993) Platinum traces in airborne particulate matter. Determination of whole content, particle size distribution and soluble platinum. Fresenius J Anal Chem 346 693-696... 

The method based on the precipitation of peroxometalate precursors enables to achieve additional purification during the process. Thus, the addition of complexonates, such as OEDP or EDTA, which form stable complexes with some polyvalent metals, prevents co-precipitation of the main impurities such as Fe, Co, Ni, Mn, Mg, etc., which in turn significantly increases the purity of the final product. Enhanced purification can also be achieved by recrystallization of the precursor. Particularly, the precipitation of ammonium peroxofluorometalates, such as ammonium peroxofluoroniobate ((NH4)3Nb04F4), as a primary precursor, leads to significant reduction of the titanium contamination. Ammonium peroxofluoroniobate, (NH4)3Nb04F4, is... 

Re-crystallization also leads to a significant reduction in the level of carbon and oxygen impurities however, the reduction of cationic impurities is usually not efficient. To prevent co-precipitation of complex fluorotantalates of polyvalent metals, some suitable complexonates are added to the solution. 

It was reported that various catalysts and reductants have been utilized in DSRP for the SO2 reduction [1-5]. In this study, appropriate catalysts were developed for DSRP. The Sn02-Zr02 catalyst was prepared by co-precipitation method and used for the catalysts in DSRP. The characteristics of SO2 reduction were investigated with CO as a reducing gas. 

Only chromium (III) co-precipitates quantitatively with hydrated iron (III) oxide at the pH of seawater, around 8. In order to collect chromium (VI) directly without pre-treatment, e.g., reduction to chromium (III), hydrated bismuth oxide, which forms an insoluble compound with chromium (VI) was used. Chromium (III) is collected with hydrated bismuth oxide (50 mg per 400 ml seawater). Chromium (VI) in seawater is collected at about pH 4 and chromium (VI) is collected below pH 10. Thus both chromium (III) and chromium (VI) are collected quantitatively at the pH of seawater, i.e., around 8. 

This survey focuses on recent developments in catalysts for phosphoric acid fuel cells (PAFC), proton-exchange membrane fuel cells (PEMFC), and the direct methanol fuel cell (DMFC). In PAFC, operating at 160-220°C, orthophosphoric acid is used as the electrolyte, the anode catalyst is Pt and the cathode can be a bimetallic system like Pt/Cr/Co. For this purpose, a bimetallic colloidal precursor of the composition Pt50Co30Cr20 (size 3.8 nm) was prepared by the co-reduction of the corresponding metal salts [184-186], From XRD analysis, the bimetallic particles were found alloyed in an ordered fct-structure. The elecbocatalytic performance in a standard half-cell was compared with an industrial standard catalyst (bimetallic crystallites of 5.7 nm size) manufactured by co-precipitation and subsequent annealing to 900°C. The advantage of the bimetallic colloid catalysts lies in its improved durability, which is essential for PAFC applicabons. After 22 h it was found that the potential had decayed by less than 10 mV [187],... 

The cycles of reduction and oxidation of Fe and Mn oxides in intermittently submerged soils provide opportunities for co-precipitation with trace metals. In most natural systems it is the rate of dissolution of the sohd phase that limits solid solntion formation rather than thermodynamics, so conditions in snbmerged soils are highly conducive to formation of solid solntions. 

The oxidized form of As, arsenate, As(V), which is present as HAs04 at neutral pH (p f values in Table 7.8), is sorbed on soil surfaces in a similar way to orthophosphate. The reduced form arsenite, As(lll), which is present in solution largely as H3As03(p fi = 9.29), is only weakly sorbed, hence mobility tends to increase under reducing conditions. Mobility will also increase without reduction of As(V) because, as for phosphate, reductive dissolution of iron oxides results in desorption of HAs04 into the soil solution. Under prolonged submergence As(lll) may be co-precipitated with sulfides. 

Co-precipitation of Re S with platinum sulfide from cone, hydrochloric acid solutions of microamounts of technetium and rhenium is suitable for the separation of technetium from rhenium , since technetium is only slightly co-precipitat-ed under these conditions (Fig. 7). At concentrations of 9 M HCl and above, virtually no technetium is co-precipitated with platinum sulfide at 90 °C, whereas rhenium is removed quantitatively even up to 10 M HCl. The reduction of pertechnetate at high chloride concentration may be the reason for this different behavior, because complete co-precipitation of technetiiun from sulfuric acid solutions up to 12 M has been observed. However, the separation of weighable amounts of technetium from rhenium by precipitation with hydrogen sulfide in a medium of 9-10 M HCl is not quantitative, since several percent of technetiiun coprecipitate with rhenium and measurable amounts of rhenium remain in solu-tion . Multiple reprecipitation of Re S is therefore necessary. 

Cu-Mn mixed-oxide binary spinel catalysts (CuxMn3 x04, where x = 0, 0.25, 0.5, 0.75 and 1) prepared through co-precipitation method exhibit phenol methylation activity imder vapor phase conditions [75]. All of the catalysts, irrespective of the compositions, produced only C-methylated phenols. However, a total ortho selectivity of 100% with 2,6-xylenol selectivity of 74% was observed over x = 0.25 compositions at 400°C. This composition was found to be relatively stable under reaction conditions compared with the other compositions studied. The catalysts with high copper content suffered severe reduction under methylation conditions whereas, catalysts with low copper content had a hausmannite phase (Mu304) that sustained... 

Unsupported V2Os—Mo03 catalysts were also studied by Bielanski and Ingolt [49,50], using an integral flow reactor at 350° C. Several hours of pre-treatment with the reaction mixture were needed to obtain a stable and selective catalyst (the catalyst was prepared from a melt instead of by the usual co-precipitation method). In this period, partial reduction and formation of V4+ (ESR analysis) take place. The activity increases with the actual V4+ concentration in the working catalyst (Fig. 7) until a 100%... 

For ageing experiments the toluene solution of the grafted polymer was first treated with an excess of triphenyl phosphine (reduction of residual hydroperoxides into alcohols), then suitable amount of the parent polymer was added and co-precipitation was performed into methanol. The polymer blend was vulcanized by adding dicumyl peroxide (5% w)prior precipitation (pressing conditions became 190°C, 190 bar, 5 min). 

Highly active Au catalysts can be prepared by an appropriate selection of preparation methods such as co-precipitation (CP), deposition-precipitation (DP), deposition-reduction (DR) and solid grinding (SG) with dimethyl Au(III) acetylacetonate, depending on the kind of support materials and reactions targeted. 

Hence, there is already an abnormally high concentration of silica on the Ni(OH)a surface prior to the reduction, and this situation will persist after reduction. The phenomenon of silica skin formation according to this hypothesis is hence inherently connected with the co-precipitation method of preparing Ni-Si02 catalysts. 

Accessibility of Co-precipitation Catalyst (54 1) after Reduction at Various Temperatures... 

The magnetic method has been applied in studying the growth of the nickel particles due to the reduction process for the co-precipitated sample 5421. Reduction treatments have been performed at various temperatures in the range 400-600° C. (for which the reduction is assumed to be complete) and during various periods of time (% to 16 hrs.). Particle sizes of the products were characterized by the magnetic parameter a. 

Species Co-precipitation with Ni(OH)2 using sodium hydroxide (% recovered) Co-precipitation with FeS following reduction with sodium borohydride (% recovered)... 

Pt-Sn-Alumina Structure. No single model will adequately describe the above catalyst characterization data and the published data that has not been included because of space limitations. The relative distribution of both the Pt and Sn species depend upon a number of factors such as surface area of the support, calcination and/or reduction temperature, Sn/Pt ratio, etc. Furthermore, it appears that the "co-impregnated" and "co-precipitated" catalysts are so different that their structure should be considered separately. 

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