STUDY OF FISCHER-TROPSCH SYNTHESIS OVER A SILICA SUPPORTED IRON CATALYST THROUGH THE USE OF REACTIVE SCAVENGERS.

摘要

The synthesis of hydrocarbons from H(,2) and CO was studied on a silica-supported Fe catalyst. The synthesis was carried out at 1.54 atm and 200 to 255(DEGREES)C in a differential reactor. Conversion of CO never exceeded 2%. The working catalyst was achieved by transforming Fe(,2)O(,3) into a mixture of Fe(,3)O(,4), bulk carbides, and iron under synthesis conditions. Synthesis product distributions and the rate of methane formation are reported. Trends in CO(,2) formation and the presence of cyclic hydrocarbons, saturated and unsaturated, suggest the presence of some Fe(,3)O(,4) at the catalyst surface. Cyclohexene addition to the feed generated low concentrations of alkyl-substituted cyclohexene and cyclohexanes consistent with reported scavenging studies over Ru. Pyridine addition to the feed generated alkyl-substituted pyridines. Additional experiments confirmed that scavenged products are not formed from the interactions between the scavenger and synthesis products on support. The results confirm that the scavengers react with species involved in chain propagation.; Pyridine was used to scavenge C(,1)-C(,3) alkyl species from the catalyst surface. The (alpha)-alkylpyridine distributions were dependent upon synthesis variables and demonstrated a dependence which was proportional to the dependence of C(,1)-C(,3) Fischer-Tropsch products. These results confirmed that alkyl species are the immediate precursors to synthesis products. Two most probably Fischer-Tropsch mechanisms were used to describe the catalytic behavior and scavenged product distributions. The alkyl fragment dependences were predicted using Langmuir-Hinshelwood expressions for these two mechanisms and were compared against the measured scavenged dependence. Lack of information concerning CO adsorption characteristics at synthesis conditions prevented discrimination between the possible mechanisms.