SYNTHESIS OF HYDROCARBONS FROM CO AND H-2 OVER SILICA-SUPPORTED RU - REACTION-RATE MEASUREMENTS AND INFRARED-SPECTRA OF ADSORBED SPECIES

The synthesis of hydrocarbons from CO and H2 was studied on a silica-supported Ru catalyst, and the species present on the catalyst surface were characterized by infrared spectroscopy. Initial rates of methane formation were correlated by the expression NCH = 5.6 × 106 exp (-24,000/RT) PH21.5 PCO0.6. The synthesis of ethane, propylene, and propane, the principle products observed in addition to methane, was favored at high CO partial pressures, low H2 CO ratios, and low temperatures. The primary feature observed in the infrared spectra was a band at 2030 cm-1, associated with chemisorbed CO. Neither the position nor intensity of this band was affected by the CO partial pressure or the H2 CO ratio. The CO band intensity did decrease with increasing temperature due to a decrease in CO surface coverage. Bands were also observed at 2950, 2910, and 2845 cm-1 and were assigned to hydrocarbon structures surrounded by chemisorbed CO. These structures could be removed from the catalyst surface by hydrogenation, but do not appear to be intermediates in the synthesis of stable products. Reduction of the catalyst following steady-state reaction revealed that the working catalyst maintains a reservoir of carbon several Ru monolayers in magnitude. Carbon deposition mechanisms and the role of carbon in the synthesis of hydrocarbons are discussed. © 1979.