Magnesia monoxide

Au°/AuI ratio decreased as the carbon monoxide pressure increased,103 the rate being maximum when this ratio was about unity. In line with this, modification of Au/MgO by ascorbic acid raised the activity, possibly because it favourably alters the Au2+/Au° ratio.109 Iron and manganese also act as promoters, perhaps by forming Mn+-Au° (M = Fe, Mn) ensembles on magnesia.110... 

Chlorination of magnesia (MgO) or magnesite (MgC03) in the presence of carbon or carbon monoxide... 

Typical ratios of carbon dioxide to carbon monoxide in the regenerator flue gas produced with uncontaminated silica-alumina, silica-magnesia, and activated-clav catalysts are shown in the following tabulation (274) ... 

The hydrocarhon-steam process involves the reaction of hydrocarbons, such as natural gas, refinery gases, or propane, with steam over a catalyst (such as nickel on magnesia) at about 800 C, to produce a mixture of hydrogen, carbon monoxide, and carbon dioxide. Starting with methane, the following reactions take place ... 

Catalytic reductions have been carried out under an extremely wide range of reaction conditions. Temperatures of 20 C to over 300 C have been described. Pressures from atmospheric to several thousand pounds have been used. Catal3rsts have included nickel, copper, cobalt, chromium, iron, tin, silver, platinum, palladium, rhodium, molybdenum, tungsten, titanium and many others. They have been used as free metals, in finely divided form for enhanced activity, or as compounds (such as oxides or sulfides). Catalysts have been used singly and in combination, also on carriers, such as alumina, magnesia, carbon, silica, pumice, clays, earths, barium sulfate, etc., or in unsupported form. Reactions have been carried out with organic solvents, without solvents, and in water dispersion. Finally, various additives, such as sodium acetate, sodium hydroxide, sulfuric acid, ammonia, carbon monoxide, and others, have been used for special purposes. It is obvious that conditions must be varied from case to case to obtain optimum economics, yield, and quality. 

Effect of particle size on turnover rate for ammonia sjmthesis. Small particles of metallic iron supported on magnesia were prepared by Boudart et The iron particle size could be changed between 1.5 run and 30 run and determined, in part, by electron microscopy. X-ray diffraction, magnetic susceptibility and Moss-bauer spectroscopy. Agreement was satisfactory with particle size values obtained by selective chemisorption of carbon monoxide (if 2 Fe for 1 CO). Two results are noteworthy, (i) The turnover rate for ammonia synthesis increases by a factor of 35 as the iron particle size increases (Table 2.12). (ii) A pretreatment of the iron catalyst with ammonia increases the turnover rate by only 10% for the larger particles, but quite appreciable for iron clusters (Table 2.13). 

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