Synthesis temperatures

Synthesis Temperature. Because of the exothermic nature of the ammonia synthesis reaction, higher temperatures increase reaction rates, but the equihbrium amount of ammonia decreases. Thermal degradation of the catalyst also increases with temperature. 

The carbon monoxide concentration of gas streams is a function of many parameters. In general, increased carbon monoxide concentration is found with an increase in the carbon-to-hydrogen ratio in the feed hydrocarbon a decrease in the steam-to-feed-carbon ratio increase in the synthesis gas exit temperature and avoidance of reequiUbration of the gas stream at a temperature lower than the synthesis temperature. Specific improvement in carbon monoxide production by steam reformers is made by recycling by-product carbon dioxide to the process feed inlet of the reformer (83,84). This increases the relative carbon-to-hydrogen ratio of the feed and raises the equiUbrium carbon monoxide concentration of the effluent. 

Another example of the use of neutron diffraction to understand the role of atomic vacancies in producing a superconducting metal oxide phase is work that has been performed on Bao Kq 4fii03. This work demonstrates that at the synthesis temperature (700° C), under the proper conditions, oxygen vacancies are created to allow the formation of the parent phase with bismuth largely in the +3 oxidation state. The presence of the vacancies allows the incorporation of potassium in the... 

Since the synthesis temperatures are higher than the dissociation temperatures of the phases that are formed (at a pressure of lO N m ), it is necessary to react the alkali metal with boron under metal pressure in excess of that defined by Eq. (a), in sealed vessels. The alkali metal is present as a liquid in equilibrium with the vapor phase, the pressure of which is determined by the T of the coldest point. This pressure (greater the more volatile the metal) favors the synthetic reaction relative to the reverse dissociation reaction. 

R ratio(H2O/TTIP)=150, synthesis temperature=180°C(HNO3) and 160 C(TENOH), dried at 105 C. obtained by Scherrer equation, apparent first-order constants(A ) of orange n. rutile structure... 

Alkali-promoted Ru-based catalysts are expected to become the second generation NHs synthesis catalysts [1]. In 1992 the 600 ton/day Ocelot Ammonia Plant started to produce NH3 with promoted Ru catalysts supported on carbon based on the Kellogg Advanced Ammonia Process (KAAP) [2]. The Ru-based catalysts permit milder operating conditions compared with the magnetite-based systems, such as low synthesis pressure (70 -105 bars compared with 150 - 300 bars) and lower synthesis temperatures, while maintaining higher conversion than a conventional system [3]. 

Which polymorphic form of a compound is formed depends on the preparation and crystallization conditions method of synthesis, temperature, pressure, kind of solvent, cooling or heating rate, crystallization from solution, fusion or gas phase, and presence of seed crystals are some of the factors of influence. 

With autoclave syntheses a high yield of clusters is achieved, and it is possible for researchers to follow the reaction path in solution by gradually changing (from experiment to experiment) the working parameters of the synthesis (temperature, pressure, exposure at working temperatures, etc). All these advantages of the autoclave technique have resulted in an abundance of new forms of technetium clusters (particularly, polynuclear ones) because it has been possible to develop and improve the method of obtaining these compounds. 

Galameau A., Cambon H., Di Renzo F., Fajula F. True microporosity and surface area of mesoporous SBA-15 silicas as a function of synthesis temperature. Langmuir 2001 ... 

These structures can be differentiated by variation of the synthetic conditions such as organic/inorganic component ratios, synthesis temperature and structure of the components, as suggested in the detailed consideration by Fujii and coworkers [69]. 

Jacobs G., Ji Y., Davis B.H., Cronauer D., Kropf J., and Marshall C.L. 2007. Fischer-Tropsch synthesis Temperature programmed EXAFS/XANES investigation of the influence of support type, cobalt loading and noble metal promoter addition to the reduction behaviour of cobalt oxide particles. Appl. Catal. A Gen. 333 179-91. 

Chapter 7 Fischer-Tropsch Synthesis Temperature-Programmed... 

FIGURE 8.5. The effect of synthesis temperature on the anisotropy of PbS nanocrystals. Anisotropy is quantified by the / -factor (rioo/fm, the ratio of the central distance of the 100 faces to that of the 111 faces). The decreasing trend is hypothesized to be due to the increased ability to overcome the activation energy necessary to grow the higher energy faces of the crystal at higher temperature. After Lee et al. 

The advent of the addition of a quaternary ammonium cation as template or structure directing agent (SDA) to the alkaline gel by Barter and coworkers, and Mobil Oil coworkers, led to the Si02 enriched zeolite A in the case of Barter and to the high silica zeolites. Beta and ZSM-5, by the Mobil group. The latter synthesis temperature typically is 100-200 °C, higher than Milton s original work. 

Spahr et al. reported in 1998 a capacity of 150 mAh/g falling to 125 mAh/g after 25 cycles and to 75 mAh/g after 50 cycles for a 550 sample prepared at 700 °C they also showed that the capacity and capacity retention increased as the synthesis temperature was increased from 450 to 700 °C, which we now know to be too low a temperature for optimum electrochemical behavior. Ohzuku et al. ... 

Figure 11. Li MAS NMR spectra of the spinel LiMn204 (structure shown on the left) as a function of synthesis temperature (adapted from ref 44). The cluster of Mn + ions formed as a result of Li substitution on the octahedral site is shown, and the resonances due to Li ions near this cluster are assigned.

Fig. 3.5 The extent of Al incorporation into the structure of goethite. Effect of a) initial Al concentration b) AI/Fe(OH)4 c) temperature. The insert in (c) shows the amount of Al incorporated per AI/(Fe-i-AI) in the system vs. synthesis temperature (a 8c b Lewis 8c Schwertmann, 1979 with permission c Schwertmann 8c Craciun, unpubi,).

Conditions which promote multi-domainic goethites are high ionic strength (either [KOH] or salt) and also low synthesis temperature (<40°C). In alkaline solutions, multi-domainic character decreases and domain width increases as Al substitution increases to Al/(Fe-i-Al) of 0.15, whereas at Al/( Al-nFe) >0.15 single domain crystals result (Schulze Schwertmaim, 1984 Mann et al., 1985). Multidomainic goethites can recrystallize to single domain crystals as a result of hydrothermal treatment at 125-180 °C (Fig. 4.9) (Schwertmann et al., 1985). 

In our previous papers (refs. 4,5) we described syntheses of VPI-5 using DPA and TBA. Since that time we have been able to crystallize VPI-5 using many other organics such as diisopropylamine, dipentylamine (DPentA), triethanolamine (TEOA), triisopropanolamine (TIPOA), cyclopentyl amine, and cyclohexyl amine at synthesis temperatures from 120 to 150 C. The wide variety of organics able to crystallize VPI-5 suggests further that the organic does not act as a template and from chemical analyses it is clear that it does not act as a space-filler. 

Effect of synthesis temperature of the precursory hectorites on the porous... 

In the FT synthesis itself, the production of aromatics is relatively low. The production does increase as the synthesis temperature is increased (see Table III) but this is accompanied by large increases in the undesirable CH. and so the FT synthesis itself is not a viable source of aromatics. 

Although this report describes the preparation of a wide variety of oxidation catalysts, only the iron modified bismuth molybdates will be described in detail. Other preparations are described in this section through an indication of the starting soluble salts and their synthesis temperatures which are the key process parameters. Other aspects of their HTAD preparations are similar to that described for the iron bismuth molybdates which follows. 

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