Fischer-Tropsch cobalt-thoria catalyst

One of the most interesting catalytic reactions to be discovered is the so-called oxo reaction. The oxo reaction consists of the catalytic addition of carbon monoxide and hydrogen to olefins to form, primarily, aldehydes possessing one carbon atom more than the original olefin. This hy-droformylation reaction was developed during World War II by Roelen and co-workers (22) in Germany. While they utilized solid Fischer-Tropsch cobalt-thoria catalyst, it became apparent to them that the hydroformylation reaction was probably a homogeneous catalytic process with either dicobalt octaearbonyl or cobalt hydrocarbonyl as the catalyst. 

The catalyst used in the process was a Fischer-Tropsch cobalt-thoria catalyst. The temperature was usually between 130-160° and a total pressure of 200 atm. of water gas (1II2 ICO) was usually employed. The reaction was carried out first with ethylene and the products were found to consist of a mixture of diethyl ketone and propionaldehyde. As both products contained a carbonyl or oxo group, the reaction was called the Oxo synthesis. Later it was found that ketone production was relatively unimportant aldehydes were almost always the principal... 

In the production of paraffins, the mixture of carbon monoxide and hydrogen is enriched with hydrogen from the water-gas catalytic (Bosch) process, i.e., shift reaction (Fig. 1), and passed over a cobalt-thoria catalyst to form straight chain (linear) paraffins, olefins, and alcohols (Fischer-Tropsch synthesis) ... 

Kinetic expressions similar to that of Equation 3 and similar activation energies have been reported for methanation over a cobalt-alumina catalyst (4) and for Fischer-Tropsch reaction over a cobalt-thoria catalyst (5). This similarity, despite appreciably different product distributions in the three cases, argues for a common rate-controlling step in the mechanisms. 

Fischer-Tropsch A process for converting synthesis gas (a mixture of carbon monoxide and hydrogen) to liquid fuels. Modified versions were known as the Synol and Synthol processes. The process is operated under pressure at 200 to 350°C, over a catalyst. Several different catalyst systems have been used at different periods, notably iron-zinc oxide, nickel-thoria on kieselgtihr, cobalt-thoria on kieselgiihr, and cemented iron oxide. The main products are C5-Cn aliphatic hydrocarbons the aromatics content can be varied by varying the process conditions. The basic reaction was discovered in 1923 by F. Fischer and... 

The exchange of methane with deuterium has been followed on nickel films 12), on a cobalt-thoria Fischer-Tropsch catalyst 13) and on films of rhodium, platinum, palladium, and tungsten 30). The important features of the exchange over the metal films may be summarized as follows ... 

The exchange of this compound has been examined quite thoroughly. Kauder and Taylor 11) used platinized platinum as a catalyst and Thompson et al. 13) used a cobalt-thoria Fischer-Tropsch catalyst. The reaction has also been studied over a series of metal films by Kemball 18) and more recently over a number of bulk metal catalysts by Addy and Bond 44)-... 

Metal molybdates421 and cobalt-thoria-kieselguhr422 also catalyze the formation of hydrocarbons. It is believed, however, that methanol is simply a source of synthesis gas via dissociation and the actual reaction leading to hydrocarbon formation is a Fischer-Tropsch reaction. Alumina is a selective dehydration catalyst, yielding dimethyl ether at 300-350°C, but small quantities of methane and C2 hydrocarbons423 424 are formed above 350°C. Heteropoly acids and salts exhibit high activity in the conversion of methanol and dimethyl ether.425-428 Acidity was found to determine activity,427 130 while hydrocarbon product distribution was affected by several experimental variables.428-432... 

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. 

Nickel, cobalt, and iron catalysts are cmnmonly used for the Fischer-Tropsch s thesis. Nickel catalysts have been prepared by precipitation from a nitrate solution with potassium carbonate in the presence of thoria and kieselguhr in the proportions lOONiilSThOzilOO kieselguhr. It is not desirable to employ nickel catalysts at low temperatures and elevated pressures because the formation of nickel carbonyl is excessive. In the temperature range of 170-220°C at. low pressures, both liquid and gaseous products are obtained. As the temperature is increased to 300-350°C and the pressure increased to 300-400 psi, nickel catalysts produce only methane. Thus, these catal nsts can be used for making a gas from coal comparable in heating value to natural gas. 

Product Selectivity. Tables III and IV summarize the product distributions for these catalysts. In Table III the kieselguhr-supported catalysts are compared. From this it is to be noted that the two most active catalysts for CO conversion are, unfortunately, highly selective towards methanation and hence are poor candidates for meeting the desired objective of producing C2-C4 olefins. The Co-Mn catalysts, however, are comparable with the modified Fischer-Tropsch catalyst (Run No. 19), cobalt-copper-thoria, which was prepared as an alkali-free... 

The experiments and results reported by Hofer, Cohn, and Peebles are as follows A 3-g. sample of raw cobalt-thoria-kieselguhr Fischer-Tropsch catalyst was reduced in flowing purified hydrogen for 40 hours at 400°. The sample was then carburized with purified carbon monoxide... 

Fischer and Tropsch went on to test a nttmber of catalysts based on niekel and cobalt supported on thoria and kieselgithr, which were considered more promising than iron. Their experimental work is a classic example of catalyst and process development that has probably since been followed by many other investigators. 

---