Microkinetic analysis of C₃–C₅ ketone hydrogenation over supported Ru catalysts

Rates of C₃-C₅ ketone hydrogenation are measured in the vapor phase over Ru/SiO₂. Reaction kinetics are considered through a range of ketone partial pressures (0.3–30 Torr), hydrogen partial pressures (90–900 Torr), and reaction temperatures (322–456 K). Ketone hydrogenation is observed to be facile, with site time yields ranging from 0.14 s⁻¹ for 2-pentanone to 0.37 s⁻¹ for acetone at 322 K and 1.2 bar H₂. At low temperatures, apparent reaction orders and kinetic barriers are similar for all ketones. During acetone hydrogenation at higher temperatures, (422 K), the ketone order increases from 0 to 0.4, while the hydrogen order increases from 0.5 to 0.9. Furthermore, the apparent barrier decreases from ≈50 kJ mol⁻¹ at 322 K to ≈18 kJ mol⁻¹. Apparent trends in hydrogenation rates are interpreted at an elementary level using a microkinetic analysis that is based on a Horiuti-Polanyi mechanism involving two distinct surface sites.