Formation of carbonaceous deposit and its effect on carbon monoxide hydrogenation on iron-based catalysts

Abstract

During carbon monoxide hydrogenation on silica-supported iron-cobalt catalysts, regardless of their iron-to-cobalt ratio or promoting with potassium, the formation of carbonaceous deposit occurs. Among iron-cobalt catalysts it takes place most quickly in the 50Fe50Co system, while the promoting of iron with potassium increases the rate of this phenomenon. Surface carbonaceous deposit causes changes in the activity of catalysts and distribution of hydrocarbons. It causes a rapid decrease in the hydrogenating ability of the catalyst, i.e. decrease in carbon monoxide conversion to hydrocarbons, and an increase in the alkenes-to-alkanes ratio. At the same time there is a rise in the percentage of shorter-chain hydrocarbons at the expense of large-molecule hydrocarbons. The general picture of changes in activity and hydrocarbons distribution caused by the carbonaceous deposit does not depend on the initial metallic phase composition, their particle size, or the amounts and quality of metal carbides. Only the rates of these changes differ as the rate of carbonaceous deposition differs.