HYDROGENATION OF CARBON OXIDES BY RU ACTIVATED CARBON CATALYSTS OBTAINED FROM RU-3(CO)(12) - EFFECT OF PRETREATMENT ON THEIR DISPERSION, COMPOSITION AND ACTIVITY

Supported Ru catalysts on activated carbons were obtained from Ru-3(CO )(12). Two activated carbons with different surface area and porosity obtained by carbonization and CO2 activation of olive stones were used as catalyst supports. The supported catalysts, once prepared, were he at treated at 673 K for 12 h in a He or H-2 flow or under high vacuum, and subsequently characterized by H-2 and CO chemisorption, transmiss ion electron microscopy and X-ray photoelectron spectroscopy. Results showed that the highest dispersion was obtained after He treatment and that Ru was present as ruthenium carbide, whereas after H-2 treatment metallic Ru was found with a lower dispersion. When the He treatment was carried out at 423 K instead of at 673 K, there was a large increa se in both the total and irreversible H-2 uptake. The CO chemisorption stoichiometry was also affected by the atmosphere of the previous tre atment. Thus, after He treatment CO was linearly chemisorbed, whereas after H-2 treatment multiple CO chemisorption predominated. Finally, t he behaviour of the catalysts in the hydrogenation reactions of CO2 an d CO was also influenced by the treatment atmosphere. Thus, for the H- 2/CO2 reaction, the methane production rate, r(CH4), decreased with re action time after He treatment, whereas it remained constant after the H-2 treatment. However, in the case of the H-2/CO reaction, r(CH4) re mained practically unchanged with reaction time after He treatment, wh ereas it underwent a large increase after the H-2 treatment.