Promoters calcium oxide

Lin, C., Wang, J., and Lunsford, J.H. Oxidative dimerization of methane over sodium promoted calcium oxide. J. Catal 1988, 111, 302-316. 

The industrial catalysts for ammonia synthesis consist of far more than the catalyticaHy active iron (74). There are textural promoters, alumina and calcium oxide, that minimise sintering of the iron and a chemical promoter, potassium (about 1 wt % of the catalyst), and possibly present as K2O the potassium is beheved to be present on the iron surface and to donate electrons to the iron, increasing its activity for the dissociative adsorption of N2. The primary iron particles are about 30 nm in size, and the surface area is about 15 m /g. These catalysts last for years. 

Dehydrochlorination of bis(tnfluoromethylthio)acetyl chloride with calcium oxide gives bis(trifluoromethylthio)ketene [5] (equation 6) Elimination of hydrogen chloride or hydrogen bromide by means of tetrabutylammonium or potassium fluoride from vinylic chlorides or bromides leads to acetylenes or allenes [6 (equation 7) Addition of dicyclohexyl-18-crown-6 ether raises the yields of potassium fluoride-promoted elimination of hydrogen bromide from (Z)-P-bromo-p-ni-trostyrene in acetonitrile from 0 to 53-71 % In dimethyl formamide, yields increase from 28-35% to 58-68%... 

Ammonia synthesis catalysts have traditionally been based on iron and have been made by the reduction of magnetite (Fe304). The difference between different commercially available products lies in optimized levels of metal oxide promoters that are included within the magnetite structure. These metal oxides promote activity and improve the thermal stability of the catalyst. Typical promoters are alumina (AI2O3X potassium oxide (K2O), and calcium oxide (CaO). The interactions between the many components in the catalyst can radically affect 1) the initial reducibility, 2) the level of catalyst activity that is achieved, 3) the long-term catalyst performance and 4) the long-term catalyst stability204. 

Calcium oxide, and other basic promoters, react with silica impurities in the raw materials to form glassy silicates. The glassy silicates enhance the thermal stability of the reduced iron. The main benefit is to minimize any neutralization of the K2O promoter, which would reduce its effectiveness204. 

Inhibition of macromolecular synthesis, mitochondrial energy metabolism, and reduction of DNA synthesis, as well as direct interaction with the cell membrane (increase in cytosolic Ca2+ concentration), have been implicated in organotin-induced cytotoxicity [169, 170]. Promotion of oxidative and DNA damage in vivo has been detected [171]. Oxidative damage and increased concentration of intracellular calcium ions seem to be the major factors contributing to triorga-notin-induced apoptosis in many cell lines [172]. 

This production of a peculiar degree of instability in the silver bromide, close to the atoms of sulphur in the sulphide, seems closely analogous to the other cases of promoter action, and the effects of a one-dimensional interface in a solid surface, which were considered in 3. It may be an effect of the same nature as the increased ease of decomposition of the calcium carbonate group, when this has calcium oxide groups adjacent to it. There is some evidence that the silver sulphide crystal lattice is rather more easily disorientated than the silver bromide, but since silver sulphide is, alone, not particularly sensitive to light, it seems certain that the sensitizing action of the sulphide speck must be due to a boundary action between the sulphide and the bromide.8... 

Direct iodination of the steroid nuclear ketones has not been described, but pregnan-20-ones are iodinated selectively at C(2i) by the action of iodine and calcium oxide [i 8]. Although the function of the latter is probably to promote enollsation in the Hofmann sense towards C(2i), the subsequent attack by iodine appears to require atoms, for it is promoted by free radical initiators. 

Table II summarizes the catalyzed gasification results of the hybrid poplar in the presence of potassium carbonate and calcium oxide. Both of these catalysts increased the liquid and gas yield at the expense of the solid. Both catalysts promoted a final product which was approximately fifty percent (50%) gaseous. The remainder of the product was thirty percent (30%) liquid and twenty percent (20%) solid.

The results of some preliminary research indicate that catalysts may be used to alter gas composition and gas yield. Specifically, potassium carbonate and calcium oxide appear to promote hydrogen production at the expense of the solid char product. 

The reaction is reversible, and CaO readily combines with CO2 to form CaC03. The pressure of CO2 in equilibrium with CaC03 and CaO increases with temperature. In the industrial preparation of quicklime, the system is never maintained at equilibrium rather, CO2 is constantly removed from the kiln to shift the equihbrium from left to right, promoting the formation of calcium oxide. 

Ammonia has been produced commercially from its component elements since 1909, when Fritz Haber first demonstrated the viability of this process. Bosch, Mittasch and co-workers discovered an excellent promoted Fe catalyst in 1909 that was composed of iron with aluminium oxide, calcium oxide and potassium oxide as promoters. Surprisingly, modem ammonia synthesis catalysts are nearly identical to that first promoted iron catalyst. The reaction is somewhat exothermic and is favoured at high pressures and low temperatures, although, to keep reaction rates high, moderate temperatures are generally used. Typical industrial reaction conditions for ammonia synthesis are 650-750 K and 150-300 atm. Given the technological importance of the... 

When flint is calcined, the combined water is driven off about 400°C, causing the large aggregates to lose their strength and become crumbly finally, at 1100°C, the quartz changes to cristo-balite, this conversion being promoted by the presence of calcium oxide, an impurity. 

The actual problem in studpng the surface chemistry of the "real" catalyst becomes evident from the inspection of an electron micrograph from the Mittasch catalyst reproduced in Fig. 6.1 [7]. The "doubly promoted" catalyst is formed from a precursor consisting essentially of Fe304 with small concentrations of potassium, aluminum, and calcium oxides as listed in the first row of the table of Fig. 6.1. The surface composition differs considerably from that of the bulk and changes further upon reduction. The working catalyst consists of particles with about 30 nm size and a specific surface area of around 20 m /g. Under reaction conditions, these... 

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