THE INFLUENCE OF LOW MOLECULAR WEIGHT OLEFINS ON CO HYDROGENATION OVER SILICA-SUPPORTED RUTHENIUM

Interactions of ethylene, propylene, and butene with H{dollar}sb2{dollar} and CO have been investigated over Ru/SiO{dollar}sb2{dollar} in an effort to understand chain growth processes occurring during Fischer-Tropsch synthesis. Product distributions are compared for the reactions of CO and H{dollar}sb2{dollar}; olefin and H{dollar}sb2{dollar}; and olefin, H{dollar}sb2{dollar}, and CO. In the latter experiments, carbon sources are differentiated by using {dollar}sp{lcub}13{rcub}{dollar}C-labeled CO and unlabeled olefin and analyzing the products by isotope-ratio gas chromatography-mass spectrometry. In the absence of CO, each olefin undergoes extensive hydrogenation. Evidence of hydrogenolysis and homologation is also observed for the three olefin/H{dollar}sb2{dollar} reactions. The observed product distributions can be described in terms of chain growth schemes involving C{dollar}sb1{dollar} and C{dollar}sb2{dollar} monomer units for ethylene homologation; C{dollar}sb1{dollar}, C{dollar}sb2{dollar}, and C{dollar}sb3{dollar} monomer units for propylene homologation; and C{dollar}sb1{dollar} and C{dollar}sb4{dollar} monomer units for butene homologation. The presence of CO enhances homologation relative to hydrogenolysis and suppresses hydrogenation.; The hydrogenation of CO to hydrocarbons is strongly influenced by the presence of C{dollar}sb2{dollar}H{dollar}sb4{dollar}, C{dollar}sb3{dollar}H{dollar}sb6{dollar}, or C{dollar}sb4{dollar}H{dollar}sb8{dollar}. Addition of C{dollar}sb{lcub}rm n{rcub}{dollar} olefin to a CO/H{dollar}sb2{dollar} feedstream suppresses the formation of hydrocarbons from CO and enhances the formation of the aldehyde C{dollar}sb{lcub}rm n{rcub}{dollar}H{dollar}sb{lcub}2{lcub}rm n{rcub}+1{rcub}{dollar}CHO and the alcohol C{dollar}sb{lcub}rm n+1{rcub}{dollar}H{dollar}sb{lcub}rm 2n+3{rcub}{dollar}OH. Ethylene is three times more effective than either C{dollar}sb3{dollar}H{dollar}sb6{dollar} or C{dollar}sb4{dollar}H{dollar}sb8{dollar} in reducing hydrocarbon formation from CO. With increasing C{dollar}sb{lcub}rm n{rcub}{dollar} olefin pressure, the overall rates of production of C{dollar}sb{lcub}rm n+{rcub}{dollar} hydrocarbons increase as a result of olefin homologation. The product distributions observed in the three olefin/CO/H{dollar}sb2{dollar} reactions are similar. Under most conditions, the fraction of CO-derived carbon atoms does not vary with carbon number. It is concluded that similar reaction pathways for chain growth are taken by CO- and olefin-derived monomer units and that the efficiency of monomer production and subsequent chain growth increases in the order CO {dollar}<{dollar} C{dollar}sb4{dollar}H{dollar}sb8 <{dollar} C{dollar}sb3{dollar}H{dollar}sb6 <{dollar} C{dollar}sb2{dollar}H{dollar}sb4.{dollar}...