The nature of hydrocarbon synthesis by means of hydrogenation of carbon monoxide on iron-based catalysts: Part I. hydrogenation-strength distribution of surface sites

The specific conditions of catalyst pretreatment are known to determine the properties of iron-based Fischer-Tropsch catalysts to a large extent. The phenomenon has been investigated and it was found that the extent of reduction of the surface has a major influence on the catalytic activity and selectivity. Methane is formed as the main product on those sites that are the first to be reduced. Further reduction of the surface results in the formation of additional sites with a lower hydrogenation activity, contributing to the synthesis of hydrocarbons according to Anderson-Schulz-Flory product statistics. The number of initial (methanation) sites, once exposed to synthesis gas, stays constant. In contrast, the number of additional (synthesis) sites depends, inter alia, on the degree of prereduction and can be varied by means of reoxidation or further reduction. Depending on the ratio of methanation to synthesis sites, a considerable amount of methane can be produced over and above that predicted by Anderson-Schulz-Flory product statistics.