Extent of reduction

The productivity of DR processes depeads oa chemical kinetics, as weU as mass and heat transport factors that combine to estabhsh the overall rate and extent of reduction of the charged ore. The rates of the reduction reactions are a function of the temperature and pressure ia the reductioa beds, the porosity and size distribution of the ore, the composition of the reduciag gases, and the effectiveness of gas—sohd contact ia the reductioa beds. The reductioa rate geaerahy iacreases with increasing temperature and pressure up to about 507 kPa (5 atm). 

Ana.lytica.1 Methods. Various analytical methods involve titration with oxidants, eg, hexacyanoferrate (ferricyanide), which oxidize dithionites to sulfite. lodimetric titration to sulfate in the presence of formaldehyde enables dithionite to be distinguished from sulfite because aldehyde adducts of sulfite are not oxidized by iodine. Reductive bleaching of dyes can be used to determine dithionite, the extent of reduction being deterrnined photometrically. Methods for determining mixtures of dithionite, sulfite, and thiosulfates have been reviewed (365). Analysis of dithionite particularly for thiosulfate, a frequent and undesirable impurity, can be done easily by Hquid chromatography (366). 

The extent of reduction of the carbonyl group of ketones and keto acids during desulfurization depends on the kind of catalyst used and on the solvent. The W 7 catalyst was most effective in reducing... 

The reduction procedure described above was carried out in a static system in order to facilitate determination of the extent of reduction in situ. The reduction was monitored gravimetrically using a microbalance (Cl Electronics MK II) and volumetrically by measuring the decrease in hydrogen pressure. Total surface areas were determined by the BET method using nitrogen at 77 K. 

In agreement with the TPR results, the hydrogen chemisorption/pulse reoxidation data provided in Table 8.3 indicate that, indeed, the extents of reduction for the air calcined samples are -20% higher upon standard reduction at 350°C (compare 02 uptake values). Yet in spite of the higher extent of reduction, the H2 desorption amounts, which probe the active site densities (assume H Co = 1 1), indicate that the activated nitric oxide calcined samples have higher site densities on a per gram of catalyst basis. This is due to the much smaller crystallite that is formed. The estimated diameters of the activated air calcined samples are between 27 and 40 nm, while the H2-reduced nitric oxide calcined catalysts result in clusters between 10 and 20 nm, as measured by chemisorption/pulse reoxidation. 

Turning to the XANES results (Figure 8.4), upon reduction at 350°C, the extent of reduction is found to be higher for the H2-activated air calcined catalysts. This is evident in the shoulder at the edge (-7,709 eV), which is a measure of metallic content, as well as the lower white line intensity for the activated air calcined catalyst at -7,725 eV. The catalysts appear to contain a combination of mainly Co metal and CoO, in agreement with the interpretation of TPR profiles previously discussed. 

If the initiation step, the activation of H2, is fast, as may be the case on noble metal oxides or highly defective oxide surfaces, the shrinking core or contracting sphere model applies (see Figure 2.3). The essence of this model is that nuclei of reduced metal atoms form rapidly over the entire surface of the particle and grow into a shell of reduced metal. Further reduction is limited by the transport of lattice oxygen out of the particle. The extent of reduction increases rapidly initially, but slows down as the metal shell grows. 

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]

In order to encourage pharmaceutical companies to invest in orphan drug development, legislation provides for a number of incentives. These include application fee waiver (the extent of reduction varies with the region of the world, and in the European Union it is 50% for all fees since 2002), market exclusivity and protocol assistance. In the European Union, there is 100% reduction in the fee applicable to the provision of any scientific advice. The fund made available by the Community for fee exemptions for orphan medicinal products amounts to= 3 700000 in 2005. 

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