Metal carbonyl-derived ruthenium/ZSM-5 and iron/ZSM-5 bifunctional catalysts for carbon monoxide hydrogenation

Some supported ruthenium catalysts have been prepared by using an extraction technique, utilizing Ru{dollar}sb3{dollar}(CO){dollar}sb{lcub}12{rcub}{dollar} as the source of the metal, cyclohexane as the extracting solvent, and the zeolite ZSM-5 as the support. The objective was to prepare Ru/ZSM-5 bifunctional catalysts which were active for CO hydrogenation and selective for aromatic and branched aliphatic components in the gasoline range. For comparison, Ru/Al{dollar}sb2{dollar}O{dollar}sb3{dollar}, Ru/SiO{dollar}sb2{dollar}, and Fe/ZSM-5 (from Fe{dollar}sb3{dollar}(CO){dollar}sb{lcub}12{rcub}{dollar}) catalysts were also prepared. The catalysts were characterized by using IR, XPS, ISS, XRD, and pyridine chemisorption studies. IR studies of the freshly prepared catalysts revealed the raped decarbonylation of Fe/ZSM-5, whereas the supported Ru catalysts displayed rich {dollar}nu{dollar}(CO) spectra. Among the latter, Ru/SiO{dollar}sb2{dollar} was the most stable, but all experienced partial oxidation and decarbonylation upon exposure to air. For the bifunctional Ru/ZSM-5 and Fe/ZSM-5 catalysts in the as-prepared state, it was evident that the metal was highly dispersed and confined to the external surface of the zeolite; obstruction of the ZSM-5 channels was minimal and the Bronsted acidity was retained. Calcination and/or reduction pretreatments resulted in varying degrees of metal aggregation, and this was dependent on the choice of metal.; Evaluation of the catalysts for CO hydrogenation was conducted at 280{dollar}spcirc{dollar}C, 20.4 atm, and with a 1:1 H{dollar}sb2{dollar}/CO mixture. Ru/ZSM-5 was much more active and more selective for higher hydrocarbons than was Fe/ZSM-5; however, the latter was more selective for aromatics. Ru/ZSM-5 which had been reduced at 400{dollar}spcirc{dollar}C was compared to the same catalyst not reduced. The former was more selective for higher hydrocarbons, while the latter was more selective for aromatics and methane; these differences were attributed to differences in metal dispersion. Activity and product selectivity were also compared for Ru/ZSM-5, a physical mixture of Ru/Al{dollar}sb2{dollar}O{dollar}sb3{dollar} and ZSM-5, and a 2-stage system comprising these components. Differences in selectivity were attributed in part to the configurations of the two catalyst functions and the relative probability of interception of Fischer-Tropsch products by ZSM-5. Metal-support interactions were apparently significant in differentiating Ru/ZSM-5 from the others. A Ru/Al{dollar}sb2{dollar}O{dollar}sb3{dollar} catalyst, which was evaluated in the absence of ZSM-5, produced no aromatics and was unusually selective for n-alkanes.