Reduction degree

Fig. 13. Flowsheet of medium pressure synthesis, fixed-bed reactor (Lurgi-Ruhrchemie-Sasol) having process conditions for SASOL I of an alkaline, precipitated-iron catalyst, reduction degree 20—25% having a catalyst charge of 32—36 t, at 220—255°C and 2.48 MPa (360 psig) at a fresh feed rate of...

Fig. 14. Fluidized-bed reactor for SASOL I (M. W. Kellogg) having process conditions of an alkaline, reduced high grade magnetite, reduction degree 95% ...

Fe(CO)s Dehydroxylated y-AfOj Adsorption from solution and thermal treatment under Ft2 at moderate T Higher dispersion, reduction degree and activity in Fischer-Tropsch than conventional catalysts [68]... 

Several factors must be taken into account when the dispersion of iron catalysts prepared by carbonyl complexes is compared to that of conventionally prepared catalysts. The iron loading and the possible formation of irreducible iron phases (by the interaction of Fe or Fe with the support) can determine a low reduction degree for conventionally prepared catalysts with low iron content and a support with high ability to react with the iron cations. In contrast, when catalysts prepared from carbonyl complexes are considered, for a given support the temperature of pre treatment which defines the hydroxyl population of the surface is a main aspect to be taken into account. For Fe/Al203 catalysts prepared from iron carbonyls and reduced after impregnation at a moderate temperature (573 K), the extent of... 

The cmc reduction degree of CyFNa by ROH is less than that of Cio SNa. The distribution coefficients of ROH between the micelle and the aqueous solution have a smaller value in the ROH-C FNa system. All these facts show the existence of "(tlutual phobicity" between FC and HC chains at the surface and in the micelles. 

Heat flux calorimeters are bioreactors equipped with special temperature control tools. They provide a sensitivity which is approximately two orders of magnitude better than that of microcalorimeters, e.g. [33,258]. The evaluation and description of microbial heat release is based on a heat balance heat yields and the heat of combustion of biological components are central parameters for quantification [70]. Measurements obtained so far have been used to investigate growth, biomass yield, maintenance energy, the role of the reduction degree of substrates, oxygen uptake [414] and product formation [272]. 

Section 4.3.2 will be devoted to the chemical characterisation studies. Because of the relationship existing between the support reduction degree and the occurrence of the deactivation phenomena mentioned above, we shall review first some of the major problems to be faced in relation to the redox characterisation of ceria and related oxide supports, sub-section 4.3.2.1. Then, we shall discuss the chemisorptive properties of these catalysts. In particular, section 4.3.2.2, will be devoted to the adsorption of H2 and CO, by far the two most commonly used probe molecules. Special attention will be paid to the relationship existing between chemisorptive behaviour and reduction temperature. We shall also report on some recent hydrogen chemisorption studies, in accordance with which, the sensitivity to the deactivation phenomena may vary from one noble metal to the other (97,117,235), being also influenced by the presence of chlorine in the support (163). 

If the results reported in Table 4.3 for the (N) and (Cl) catalysts are compared, some dramatic differences may be noted. Thus, the ex-chloride sample reduced at 623 K shows an overall reduction degree, 22.1%, much larger than that exhibited by the (N) catalyst, 11.4%. Likewise, the effect of the evacuation treatment at 773 K is very different on the (Cl) and (N) samples. In the (Cl) catalyst, the irreversible contribution represents as much as the 90% of the total reduction degree. For the (N) sample, this contribution is much smaller, 36% for the sample reduced at 623 K, and 45% after reduction at 773 K. 

As deduced from the magnetic balance results commented on above, also confirmed by XAS data (205), the use of chlorine-containing metal precursors may deeply modify the redox properties of ceria. The reversible contribution plays a minor role, thus suggesting that the presence of chlorine heavily disturbs the H2-CeC>2 interaction (209). This has also been confirmed by some volumetric (209) and TPD studies (166), Likewise, the above results show the existence of a new very important contribution to the total reduction degree reached by ceria. It is specifically related to the Cr ions incorporated into the ceria lattice. Though it does not revert on outgassing, no oxygen vacancies would be associated with this third contribution (52,163,193,195). 

The oxygen consumption data in Table 4.4 are expressed as apparent 0/Rh ratios. The ceria reduction degree was determined as the difference between the total oxygen uptake (Pulses + TPO) and the one assigned to Rh. The 0/Rh value assigned to the metal re-oxidation was assumed to be 1.5. As deduced from Table 4.4, this O2 uptake is equivalent to a 12% reduction of ceiia, being therefore far lh>m negligible. 

If only two components of fixed shape exist, corresponding to the two redox states (as indicated by the FA studies), then the analysis can be simplified as done by Appel et a. [119] the Ce component (obtained from a pure CeOj spectrum) can be subtracted from a given spectrum in amounts appropriate to cancel the u peak the Ce fraction is thus obtained, which allows to quantify both. It should be noted that this conclusion of the FA contradicts the above mentioned claims of non-linear relationship between the u peak area and total reduction degree. One may note here that the FA results [111, 117] reproduce the small shake-up satellites described above as part of the Ce component the latter of these overlaps the u peak of Ce, and if not taken into account may contribute to the non-proportionality between %(u ) and the amount of Ce". The presence of a small component near the u peak position is visible in other spectra of nominally pure trivalent Ce [120]. 

Also, earlier works [121] suggest a nearly linear dependence between the v peak intensity and the reduction degree which is not a pure proportionality, as it includes some (u -v ) peaks intensity in the pure Ce state (Fig. 5.11) this might correspond to the mentioned satellite located near the u peak. 

Another method of analysis makes use of a subtraction procedure and has been applied to investigate the oxidation state of a series of Ce-Zr mixed oxides during a temperature programmed process [195]. A difference spectrum between the sample at a defined state and the calcined, fully oxidized material displays a positive peak at the position of feature Bo, characteristic of Ce, and a negative peak at the position of feature C, characteristic of Ce. The overall peak-to-peak amplitude is then proportional to the average reduction degree of Ce in the sample. 

Purchased from Kawaken Fine Chemicals Pd-distribution Uniform Reduction degree 25-99% Pd dispersion . 16% Water content 1.8%. 

Purchased from Degussa. lapan Co., Ltd., Catalysis Division Pd-distribution Egg shell hnpregnation depth 50-150 nm Reduction degree 0-25% Pd dispersion 29% Water content 3%. 

Fig. 2. Change in the reduction degree of iron oxides during reduction with hydrogen (Step 1) at 603 K and reoxidation with water vapor (Step 2) at 653 K. A Fe-oxide(urea), Fe-oxide(NH3) and 0 Fe-oxide(W).

Cr-Fe-oxide(urea)> pjg 3 change in the reduction degree of iron oxides during... 

Indeed, the H2(ext/obs) ratio which is a measure of the reduction degree and therefore indicates if there is an interaction with the zeolite or between cerium and vanadium, exhibited different values, depending on the way of introduction and species formation. The catalyst treated with steam, EXV, presented a low H2 (ext/obs) ratio, which indicates a better reduction. On the other hand, the impregnated catalyst (IMPV) presented a high H2 (ext/obs) ratio, and thus low reduction. This could explain the indication that an interaction occurred during the treatment, with the formation of bimetallic or alloys or even the formation of aluminum silicate-metal interaction. 

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