Promoters magnesia

In the presence of the promoter used, the mean Ni crystallite size in the promoted magnesia supported nickel catalyst increases according to the following order Al203> MgO>CaO. 

Leveies, L., Seshan, K., Lercher, J.A., and Leffert, L. Oxidative conversion of propane over hthium-promoted magnesia catalyst n. Active site characterization and hydrocarbon activation. J. Catal. 2003, 218, 307. 

Sol—Gel Sintered Aluminum Oxide. A new and much more versatile sintered alumina abrasive is now produced from aluminum monohydrate, with or without small additions of modifiers such as magnesia, by the sol—gel process (see Sol-gel technology). The first modified sol—gel abrasive on the market, Cubitron, was patented (27) and produced by the 3M Corporation for products such as coated belts and disks. The success of this material promoted intensive research into sol—gel abrasives. 

Extensive research has been conducted on catalysts that promote the methane—sulfur reaction to carbon disulfide. Data are pubhshed for sihca gel (49), alurnina-based materials (50—59), magnesia (60,61), charcoal (62), various metal compounds (63,64), and metal salts, oxides, or sulfides (65—71). Eor a sihca gel catalyst the rate constant for temperatures of 500—700°C and various space velocities is (72)... 

In some parts of the world, as in Russia, fermented alcohol can serve as a cheap source for hutadiene. The reaction occurs in the vapor phase under normal or reduced pressures over a zinc oxide/alumina or magnesia catalyst promoted with chromium or cohalt. Acetaldehyde has been suggested as an intermediate two moles of acetaldehyde condense and form crotonaldehyde, which reacts with ethyl alcohol to give butadiene and acetaldehyde. 

This paper identifies alumina, rare earths, platinum, and magnesia as important SOx capture materials. Alumina is either incorporated directly into the matrix of a cracking catalyst or added as a separate particle. Cerium is shown to promote the capture of SO2 on high alumina cracking catalyst, alumina, and magnesia. Other rare earths are ranked by their effectiveness. The promotional effect of platinum is shown between 1200 and 1400 F for SO2 capture on alumina. Silica, from free silica or silica-alumina in the matrix of cracking catalyst, acts as a poison by migrating to the additive. 

The promotional effect of cerium is not confined to alumina as shown by the data for magnesia (26) in Table II. 

Ermakova and co-workers manipulated the Ni particle size to achieve large CF yields from methane decomposition. The Ni-based catalysts employed for the process were synthesized by impregnation of nickel oxide with a solution of the precursor of a textural promoter (silica, alumina, titanium dioxide, zirconium oxide and magnesia). The optimum particle size (10 0 nm) was obtained by varying the calcination temperature of NiO. The 90% Ni-10% silica catalyst was found to be the most effective catalyst with a total CF yield of 375 gcp/gcat- XRD studies by the same group on high loaded Ni-silica... 

The formation of the mixed compounds is reflected in the activity of the potassium promoted system, which is below that of, e.g. potassium/iron-on-magnesia [3], The absence of both potassium ferrite, believed to be the active phase, and potassium carbonate, necessary for gasification of deposited carbon, might be responsible for the observed behavior. 

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... 

Table VIII presents analytical data for other nitrided catalysts (two fused and one precipitated) after use in the synthesis with 1H2 + ICO gas. The fused catalysts containing alumina (D3008) and zirconia (L3028) as structural promoters were more resistant to oxidation during synthesis at 21.4 atm. than was the catalyst promoted with magnesia (D3001). Nitrogen was removed more rapidly from the catalyst containing alumina (D3008) during synthesis at 21.4 atm. than at 7.8 atm. The analyses of catalyst P3003.24 indicate that nitrided, precipitated catalysts are also resistant to oxidation.

Historical Development and Future Perspectives The Fischer-Tropsch process dates back to the early 1920s when Franz Fischer and Hans Tropsch demonstrated the conversion of synthesis gas into a mixture of higher hydrocarbons, with cobalt and iron as a catalyst [35, 36], Some 20 years earlier, Sabatier had already discovered the reaction from synthesis gas to methane catalyzed by nickel [37]. The FTS played an important role in the Second World War, as it supplied Germany and Japan with synthetic fuel. The plants used mainly cobalt catalysts supported on a silica support called kieselguhr and promoted by magnesia and thoria. 

Another test of validity is to check the performance of the model against experimental rate data obtained far from equilibrium. The microkinetic model presented in Table 7.3.1 predicts within a factor of 5 the turnover frequency of ammonia synthesis on magnesia-supported iron particles at 678 K and an ammonia concentration equal to 20 percent of the equilibrium value. This level of agreement is reasonable considering that the catalyst did not contain promoters and that the site density may have been overestimated. The model in Table 7.3.1 also predicts within a factor of 5 the rate of ammonia synthesis over an Fe(lll) single crystal at 20 bar and 748 K at ammonia concentrations less than 1.5 percent of the equilibrium value. 

Comparison of calculated and measured ammonia concentrations at the effluent of a steady-steady ammonia synthesis reactor containing ruthenium particles supported on magnesia and promoted by cesium. [Adapted from O. Hinrichsen. F Rosowski, M. Muhler, and G. Ertl, The Microkinetics of Ammonia Synthesis Catalyzed by Cesium-Promoted Supported Ruthenium, Chem. Eng. Sci., 51 (1996) 1683, copyright 1996, with permission from Elsevier Science.]... 

The ratio of CO2 to CO with Filtrol SR catalyst has been reported to be 1.2-1.3, closely resembling that obtained with synthetic silica-alumina (326). The ratio tends to increase with use for silica-alumina catalyst but not with silica-magnesia (355). The increase with silica-alumina is presumably due, at least in part, to accumulation of metal contaminants that promote complete combustion to CO2 total iron pick-up during commercial use was reported to be much less in the case of silica-magnesia than in a companion commercial run on silica-alumina (355). Intentional addition of a small amount of chromium to TCC bead catalyst is practiced commercially for the specific purpose of insuring complete combustion to CO2 and thereby avoiding afterburning (333). 

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