Promoters thoria

Jacobs, G., Patterson, P.M., Graham, U.M., Crawford, A.C., Dozier, A., and Davis, B.H. 2005. Catalytic links among the water-gas shift, water-assisted formic acid decomposition, and methanol steam reforming reactions over Pt-promoted thoria. J. Catal. 235 79. 

Ha2ards encountered with tungsten may be caused by substances associated with the production and use of tungsten, eg. As, Sb, Pb, and other impurities in tungsten ores, Co aerosols and dust in the carbide industry, and thoria used in welding electrodes. Lanthanum is being promoted as a substitute for thoria in this appHcation. 

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. 

Relatively little work has been done with carbon dioxide reduction for the fonnation of methane, however, because of the waste (if hydrogen involved when the process is considered from an economic standpoint. Promoter action of thoria on nickel has been studied by Taylor and Russell," the interaction of hydrogen and carbon dioxide on the surfaces of platinum and tungsten by Prichard and Hinshelwood,10" and the formation of formaldehyde by the action of carbon dioxide, hydrogen and... 

To obtain good conversion by reaction (4) even with an excess of steam It is necessary to use an active catalyst in order to operate at a temperature lower than 1000° C. Nickel catalysts, promoted with alumina or thoria and supported on fire clay, magnesium oxide, or brick, are very suitable for the process, giving essentially equilibrium conversion at low rates of gas flow through the converter. At increasing rates of flow the increase in unconverted methane is practically linear with the increase in space velocity. ... 

The iso synthesis, which is a variation of the higher-alcohol process, produces in addition to the higher alcohols, branched-chain and cyclic hydrocarbons. The catalyst used consists chiefly of thoria. When promoted with allcali, the catalyst is useful in increasing the average molecular weight of the products. At 400°C the iso synthesis produces a mixture of alcohols and hydrocarbons, whereas at 450°C hydrocarbons (largely isobutane) are the principal products. 

It is recommended that electrodes to be used for DC negative-polarity welding be of the 2% thoria type and be ground to a truncated conical tip. Excessive current will cause the electrode to overheat and melt. Too low a current will permit cathode bombardment and erosion caused by the low operating temperature and resulting arc instability. Although a sharp point on the tip promotes easy arc starting, it is not recommended because it will melt and form a small ball on the end. 

Many other iron catalyst compositions have been examined experimentally as the styrene process has developed." Chromium was replaced or combined with a wide range of other oxide promoters, such as copper oxide, zinc oxide, vanadium pentoxide, thoria, tungsten oxide, molybdena, ceria, and alkaline earth oxides. At the time, none was used in any full-scale process but some were later found to give good performances in improved plants. 

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