Catalytic effect of iron on decomposition of carbon monoxide: II. Effect of additions of H₂, H₂O, CO₂, SO₂ and H₂S

Abstract

In this work the effect of additions of H₂, H₂O, CO₂, SO₂, and H₂S on the catalytic decomposition of CO by iron has been investigated at 400, 600, and 800°C and atmospheric pressure. The catalyst was porous iron formed by the reduction of hematite ore granules with hydrogen. The relative importance of carbon deposition by the reactions 2CO → C + CO₂ and H₂ + CO → C + H₂O was determined as a function of hydrogen concentration. It was found that even low concentrations of hydrogen greatly enhanced the rate of decomposition of CO, presumably by a catalytic action of adsorbed hydrogen on iron. The presence of water vapor had a dual effect. At low concentrations of hydrogen the rate of decomposition of CO increased with the addition of H₂O, apparently by a catalytic effect. At high concentrations of hydrogen, however, carbon deposition was retarded because of the effect of the reverse reaction H₂O + C → H₂ + CO. In CO-CO₂ mixtures the rate of carbon deposition decreased with increasing CO₂ content, because of the effect of the reverse reaction CO₂ + C → 2CO. The presence of traces of sulfur-bearing gaseous species, such as SO₂ and H₂S, retarded the decomposition of CO on iron and brought about the early cessation of carbon deposition. This strong effect may be due to the retardation of the decomposition of the intermediate product, cementite, and the formation of pyrrhotite on the surface of the iron catalyst.