Changes in the surface structure and composition of an iron catalyst of reduced or unreduced Fe 2O 3 during the reaction of carbon monoxide and hydrogen

Abstract

Iron oxide (Fe 2O 3) prepared by decomposition of iron nitrate acquires a catalytic activity in the CO + H 2 (1 atm) reaction at 250 °C even without any reduction pretreatment in H 2. The nonreduced catalyst and the reduced one have their surface and bulk compositions modified in different ways. In both cases the surface is covered by carbon and a small fraction of it is directly involved in the Fischer-Tropsch reaction with H 2, whereas the remainder is transformed into carbide not involved in the Fischer-Tropsch reaction or stays as inactive carbon. The formation of iron carbide is faster for the reduced sample and must be correlated with a higher rate of deactivation of this sample than of the nonreduced sample. A sequence of steps, different for the nonreduced and the reduced catalysts, is proposed, and accounts for the higher Fischer-Tropsch activity of the former material.