Abstract
The behavior of unpromoted and K-promoted Fe/Al 2O 3 catalysts in both, CO 2 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 Mössbauer 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, CO 2 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 CO 2 hydrogenation compared to CO hydrogenation. Higher selectivities to C2–C4 alkenes were obtained from the first reaction through promotion with K.
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