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In the NASA-developed Bosch process, CO/sub 2/ is reduced with hydrogen to form carbon and water. CO and methane are also formed. Carbon accumulates in the reactor and water is removed in the recycle gas stream. Normally an iron catalyst is used. In this study, cobalt and nickel catalysts were studied to overcome the limitation that iron readily oxidizes to a noncatalytic form and this limits the extent of reaction. It was shown that cobalt and nickel catalysts allow much higher exit water concentrations, but still it is not possible to attain the equilibrium predicted from assuming the product carbon is ..beta..-graphite. It is postulated that carbon deposits as a metastable metal-carbide intermediate and, therefore, water yields are limited by the metal-carbide equilibrium. The effect of this carbide route to carbon formation is very pronounced at 700 K and below, but it is less important at higher temperatures.

Experiments were conducted to measure carbon deposition from gas mixtures containing CO, CO/sub 2/, H/sub 2/, H/sub 2/O, and CH/sub 4/. The temperature was 823/sup 0/K and the pressure 1 atm. An iron catalyst was employed. It was concluded that two conditions have to be satisfied before carbon deposition occurs, viz. the thermodynamics must be favorable for carbon deposition and the gas phase composition must not lie in ranges where the iron oxidizes or carbides as neither of these appear to be a catalyst for carbon deposition reactions. The formation of an oxide or carbide may be treated as a restraint to the attainment of reaction equilibria in the carbon deposition process.