Hydrogenation of carbon oxides over Fe/Al2O3 catalysts

The behavior of unpromoted and K-promoted Fe/Al2O3 catalysts in both, CO2 a nd CO hydrogenation reactions at 553-563 K and 1.2 MPa was compared. To att ain different degrees of interaction between Fe and the support, three diff erent procedures were followed to prepare the catalysts: impregnation, prec ipitation and physical mixing of the support with Fe oxide obtained from ci trate decomposition. Fe-phase composition of pretreated (reduction-carburiz ation) and after reactions catalysts was analyzed by Mossbauer spectroscopy . Correlation between Fe phase composition of pretreated catalysts and prod uct selectivity was evident. A lower proportion of carbided Fe in fresh cat alysts led to higher methane selectivity and higher alkanes/alkenes and int ernal/terminal alkenes ratios for both reactions, CO2 and CO hydrogenation. This relationship was observed independently of the reoxidation of carbide to magnetite, which took place during reactions for most catalysts. Lighte r hydrocarbons were produced from CO2 hydrogenation compared to CO hydrogen ation, Higher selectivities to C2-C4 alkenes were obtained from the first r eaction through promotion with K. (C) 1999 Elsevier Science B.V. All rights reserved.