Hydrogenation of carbon oxides over Fe/Al2O3 catalysts

The behavior of unpromoted and K-promoted Fe/Al2O3 catalysts in both, CO2 and CO hydrogenation reactions at 553-563 K and 1.2 MPa was compared. To attain different degrees of interaction between Fe and the support, three different procedures were followed to prepare the catalysts: impregnation, precipitation and physical mixing of the support with Fe oxide obtained from citrate decomposition. Fe-phase composition of pretreated (reduction-carburization) and after reactions catalysts was analyzed by Mossbauer spectroscopy. Correlation between Fe phase composition of pretreated catalysts and product selectivity was evident. A lower proportion of carbided Fe in fresh catalysts led to higher methane selectivity and higher alkanes/alkenes and internal/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. Lighter hydrocarbons were produced from CO2 hydrogenation compared to CO hydrogenation, Higher selectivities to C2-C4 alkenes were obtained from the first reaction through promotion with K. (C) 1999 Elsevier Science B.V. All rights reserved.