Chemical Reaction During Preparation Process

Equation (4.1) is the main reaction in the preparation of conventional Fe304-based catalysts. Due to the very low content of Fe2 03 in magnetite, the preparation of conventional Fe304-based catalysts is mainly a physical melting process. In refined natural magnetite, the Fe +/Fe + ratio is less than 0.5, while the generally 

Fe +/Fe + ratio of conventional Fe304-based catalysts is in the range of 0.5-0.7. Also, Fe + can easily be oxidized into Fe + in the air, further decreasing the ratio of Fe +/Fe + during the preparation  

Therefore, during the melting process, the reductant must be added into the furnace to adjust the ratio of Fe +/Fe +  

The ratio of Fe +/Fe + (or called oxidation degree) is the main controlled parameter during the preparation process, and should be measured at a certain period of time. 

Fc203 + reductant — Fc304 Fc304 + reductant — 4FeO 

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Solid state reactions discussed here refer to the reactions which have at least one solid as reactants or products. Both the preparation and reduction of fused iron catalyst are solid state reaction processes, but the role of solid reaction has never been studied thoroughly yet, although there are few reports in literatme and textbooks on the preparation and reduction of fused iron catalyst. There is no doubt that the basic reactions during preparation and reduction of fused iron catalysts belong to orderliness of solid state reactions. The reduction and oxidation of solid oxide, the decomposition of carbonates and hydrates, and the oxidation of sulfides etc belongs to solid state reaction. The solid state reaction follows its imique law, and it must be considered in the analysis and interpretation of preparation and reduction of fused iron catalyst. Therefore, it should be understood on the basic law of solid state chemical reactions. 

A variety of metal catalysts are commonly used with their oxides as precursors. The oxide may undergo chemical reaction with support, and reactions may take place between the components in multi-component metal catalysts during preparation process. Thus, TPR peaks of each oxide will be different from its pure oxides. In other words, the interaction between metal components and support or between metal components can be studied by TPR method for metal catalysts. The sensitivity is so high that it can detect the reduction reaction with consumption of only 10- mol H2. 

The most important experimental task in structural chemistry is the structure determination. It is mainly performed by X-ray diffraction from single crystals further methods include X-ray diffraction from crystalline powders and neutron diffraction from single crystals and powders. Structure determination is the analytical aspect of structural chemistry the usual result is a static model. The elucidation of the spatial rearrangements of atoms during a chemical reaction is much less accessible experimentally. Reaction mechanisms deal with this aspect of structural chemistry in the chemistry of molecules. Topotaxy is concerned with chemical processes in solids, in which structural relations exist between the orientation of educts and products. Neither dynamic aspects of this kind are subjects of this book, nor the experimental methods for the preparation of solids, to grow crystals or to determine structures. 

One key in dehning structural evolution, and thus, the resulting characteristics of the hnal him, is the chemical reactions that occur (intended or otherwise) during solution preparation. These reactions have been investigated in great detail for a variety of material systems, and the basic reaction chemistry for the more common processes is well understood. This chemistry lends itself to categorization into three divisions sol-gel, chelate, and metallo-organic decomposition (MOD) processes. These processes and their associated reaction chemistries are discussed below, prior to discussion of the role of solution species nature on structural evolution. 

As for sol-gel processes, the product of the reactions in chelate processes is small oligomeric species that generate either chemical or physical gelation during film preparation. Although the nature of the species has not been... 

To prepare hexaaluminates for ceramic applications a slightly different sol-gel process was proposed by Debsikbar.19 Ba-hexaaluminates were prepared via hydrolysis of Al di(isopropoxide) acetoacetic ester chelate and anhydrous Ba acetate obtained by reaction between BaC03 and glacial acetic acid. The substitution of Al(i-OC3H7)3 with the alkoxy ester was intended to control the chemical polymerization during gel formation. The reaction was performed in 1-butanol. The formation of the gel slowly occurred at room temperature in about 10 h. To obtain the final phase the gel precursor was dried at 70 °C for about 2 weeks, ground and calcined at 1200°C for 2 h. However no data on the morphology of the final materials were reported by the author. 

In-process Material Any material fabricated, compounded, blended, or derived by chemical reaction that is produced for, and used in, the preparation of the drug product (21 CFR 210.3(b)(9)). For drug substance, in-process materials are considered those materials that are undergoing change (e.g., molecular, physical). Intermediate A material produced during steps of the synthesis of a dmg substance that must undergo further molecular change before it becomes a dmg substance. 

In the variety of excitation or de-excitation processes that allow the preparation and/or observation of the system via the participation of the continuous spectrum, the dominant and most interesting characteristics are generated by the transient formation of nonstationary or unstable states. For example, the excitation may be caused by the absorption of one or of many photons during the interaction of an initial atomic or molecular state with pulses of long or of short duration. Or, the transient formation and influence on the observable quantity may occur during the course of electron-atom scattering or of chemical reactions. 

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