Monoxide phase, fundamental reactions

The identification of catalytically active species in FTS is of fundamental importance, as an improved understanding could enable the development of catalysts with increased activity and selectivity. In cobalt- and ruthenium-catalysed FTS, metallic cobalt and ruthenium function as active catalysts. However, in iron-catalysed FTS there are several distinct species generated during the reaction. Due to the lower, or similar, activation energy for iron carbide formation in comparison to carbon monoxide hydrogenation, iron-carbide formation is typically observed in FTS. The formation of several iron-carbide phases have been observed -Fe2C/8 -Fe2.2C (hexagonal... 

Studies of the reaction mechanisms for a number of simple compounds in supercritical water have been carried out, but even these seem to be complex. For example the oxidation of carbon monoxide can involve 21 elementary reactions [23]. Computer modelling is required and programs designed for combustion processes are sometimes used. The rates of oxidation of carbon monoxide are substantially lower than those predicted by gas-phase models and the proportion of hydrogen produced by the concurrent water-gas shift reaction is unexpectedly high. The differences are explained in terms of lower diffusivities compared with the gas phase, as a result of solvent cages . Because of difficulties with fundamental studies, much work on reactions is empirical and directed towards particular processes. Some of this work relevant to toxics destruction is given in the next section. 

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