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Structure and Reactivity of Bimetallic FeIr/SiO2 Catalysts after Reduction and during High-Pressure CO Hydrogenation

“…CO hydrogenation, EXAFS, and Mössbauer spectroscopy clearly reveal that the structure and composition of the 1 : 1 FeIr/SiO 2 catalyst changes significantly during the time that the catalyst reaches steady-state conversion conditions. Infrared spectroscopy and ethylene hydrogenation experiments reported in (26) confirm that the reactivity of the surface changes drastically as well. The main structural changes appear associated with the iron in the catalyst.…”

“…The Ir/SiO 2 catalyst is the least active in both methanol synthesis and ethylene hydrogenation, both after initial reduction and prolonged use in CO hydrogenation. Thus, the surface active for methanol synthesis is capable of hydrogenating ethylene in the presence of CO. As ethylene hydrogenation (in the absence of CO) occurs readily on most group-8 metals, we believe that the hydrogenation activity of the FeIr catalysts is associated with the adsorption strength of CO and thus with the extent that hydrogenation is poisoned by adsorbed CO. Support for this view is provided by the CO desorption studies as reported in (26).…”

“…(26) show that the increased hydrogenation activity of the activated FeIr/SiO 2 catalyst is accompanied by a significantly weakened adsorption strength of CO. These results thus suggest that Ir or FeIr surfaces modified, such that they adsorb CO only weakly, have a relatively high activity for hydrogenation, which is favorable for the formation of methanol from CO.…”

“…The ethylene hydrogenation experiments in (26) suggest that a clear correlation exists between the selectivity of the catalysts for methanol formation and their activity for ethylene hydrogenation in the presence of CO. The fresh 1 : 1 FeIr/SiO 2 catalyst has a low activity both for methanol synthesis and for ethylene hydrogenation.…”

“…FeIr/SiO 2 has been chosen because it is the most active and most stable methanol synthesis catalyst of the FeM/SiO 2 family (5). In a recent letter (26) we used temperature programmed desorption of CO as monitored by infrared spectroscopy to show that Fe-Ir catalysts in their active state for methanol production adsorb CO much weaker than freshly reduced catalysts do. In addition, the activated Fe-Ir catalysts had much higher activity for the hydrogenation of ethylene in syngas, indicative for higher coverages of hydrogen on the catalyst in its active state.…”