Aluminium oxide surface reactions synthesis

Synthesis of ammonia. The synthesis reaction is dependent on the conditions of equilibrium and the kinetics of the reaction. The latter is dictated by the efficacy of the catalyst, which in turn is chosen because of its cheapness and activity. Iron is the only realistic catalyst, but its activity can be greatly increased by the use of suitable promoters. It is prepared by melting iron oxide, refractory oxides such as potassium and aluminium oxides. A solid sheet forms on cooling, and is broken down into 5-10 mm lumps. The whole is then reduced in the ammonia synthesizer, where the oxide is converted to iron crystallites separated by the refractory oxides and covered in part by KOH as a promoter. The KOH can enhance the reactivity twofold. This catalyst must be used within the temperature range 400°-540 °C. Below this the catalyst becomes uneconomically inactive above, it sinters and loses surface area. An improved iron catalyst of higher activity and longer life is a feature of the AMV process. It is important to note that much of the reason for improved and continued activity is due to the careful removal of poisons such as CO, CO2, and H2S. 

The above results show that post synthesis alumination of PSM with AlfNOjfi improves the hydrothermal stability of the resulting AMM material. Similar effect has been observed by Mokaya et al. [12], who reported that the hydrothermal stability of MCM-41 could be enhanced by reaction with chlorohydrate of aluminium. Moreover, from the study of high Si/Al ratio of Y zeolite, Lutz et al. [13] reported that the hydrothermal stability of Y zeolite was enhanced by an external introduction of non-structural aluminum species onto the surface of Y zeolite. The surface layer of Al-rich aluminosilicate or aluminum oxide was suggested to block the terminal OH groups and energy-rich =Si-0-Si= bonds on the surface of Y zeolite, hence minimizing the attack of water molecules on the framework. Due to these properties, the non-structural... 

The reaction requires the use of a catalyst for the alkaline earth metals, rare earth metals and aluminium. The most common approaches are the use of (in the laboratory practice only) the salts of mercury(II) such as HgC or Hg(OAc)2. Very small portions of these salts cause amalgamation of the metal surface (and thus clean it from the oxide layer) and facilitate the reaction with alcohols. The larger scale synthesis (and thus the industrial one—in the scope of pollution danger) uses the initial addition of solid iodine (1 g or less per 1(X) g ofalkoxide to be prepared). Formation of metal iodide serves both for cleaning the surface and increases also slightly the acidity of alcohols via formation of solvate complexes. In the case of barium, the application of dry ammonia gas has been reported for this purpose (Caulton, 1990 Drake, 1992). The major factor facilitating the reaction ofmetals with alcohols is the solubility of the alkoxides formed. Insoluble alkoxides form a protective layer on the surface of the metal and it hinders the reaction. Even the reaction of sodium with BuOH in toluene may be almost stopped by the formation of poorly soluble NaO Bu. 

---