Process absorption-reduction

Temperature-programmed reduction combined with x-ray absorption fine-structure (XAFS) spectroscopy provided clear evidence that the doping of Fischer-Tropsch synthesis catalysts with Cu and alkali (e.g., K) promotes the carburization rate relative to the undoped catalyst. Since XAFS provides information about the local atomic environment, it can be a powerful tool to aid in catalyst characterization. While XAFS should probably not be used exclusively to characterize the types of iron carbide present in catalysts, it may be, as this example shows, a useful complement to verify results from Mossbauer spectroscopy and other temperature-programmed methods. The EXAFS results suggest that either the Hagg or s-carbides were formed during the reduction process over the cementite form. There appears to be a correlation between the a-value of the product distribution and the carburization rate. 

Flow of Two Fluids. The major applications are in absorption, extraction, and distillation, with and without reaction. Other applications, also quite important, are for shell-and-tube or double-pipe heat exchangers, and noncatalytic fluid-solid reactors (blast furnace and ore-reduction processes). 

The substitution of fluorine atoms for the hydrogens at the bridging position results in a bathochromic shift of the absorption maximum by 38 nm and shifts to more positive potentials for both the oxidation and reduction processes. Some oligomers (355-358) have been investigated. 

The transient absorption spectrum in Fig. 7 shows the formation of a radical anion of oxazine 725 following the excitation of humic acid adsorbed on Ti02 particles. A similar approach has also been employed recently to reduce Cr(VI) ions using humic acid/ZnO system [250]. The use of humic acid in such a semiconductor mediated reduction process has significant environmental implications. The presence of naturally occurring metal oxide semiconductors in soil systems along with humic substances presents a possible pathway for natural reductive processes to clean up the environment. 

The biochemical processes of denitrification and Fe(III) reduction have been experimentally investigated in a batch reactor [5]. The feasibility of the integrated absorption-bioreaction process was demonstrated on a laboratory-scale setup [6], Figure 12.1 presents the principle of a biochemical process for NO removal (BioDeNOx). 

Li reacts readily with N2 to form Li3N. We have had an indication that other Li-N compounds of different stoichiometry can also be formed [15,18], However, these reactions only take place in an 02-free atmosphere. Hence, in a usual glove box atmosphere from which 02 is continuously removed, while N2 may exist in a concentration of hundreds of ppm, freshly prepared Li surfaces may always be covered by Li3N film. This film has a typical absorption in the IR, appearing as a broad peak around 680 cm1 [18]. Li3N is a strong base and nucleophile which can further react with alkyl carbonate and ester solvents [18]. In solutions, the reaction between Li and N2 is much less important, due to competition with other reduction processes (of solution species). 

As already discussed, reactions at extended electrodes and particles differ only insofar as, at particles, both an oxidation and a reduction process always occur simultaneously. There is, however, one further aspect which may be of importance for using big or small particles. Taking two solutions containing semiconductor particles of different sizes, i.e. for instance of 3 nm and 4 /im, then many more particles are present in the solution containing the 3 nm-particles than in that of 4 /im-particles, provided that the concentration of the semiconductor material is identical in both solutions. As it can easily be calculated, a time interval of 5.4 ms exists between the absorption of two photons in one individual 3 nm-particle for a photon-flux of 4 x 10 cm s assuming that all photons are absorbed in the colloidal solution [114]. In the case of the 4 pm-particles, the time interval is about 20 ps for the same photon flux, i.e. it is shorter by a factor of 10 , compared to the time interval estimated for the 3 nm-particles. This can be important for reactions where two or more electrons are involved, typical in many oxidation- and reduction reactions with organic molecules [114]. 

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