Influence of crystallite size on acetone hydrogenation over copper catalysts.

Acetone hydrogenation was studied over a family of Cu/SiO2 catalysts as well as UHP Cu powder and a Cu chromite catalyst. Oxygen chemisorption via dissociative N2O adsorption was used to count surface Cu atoms and calculate crystallite sizes, and a microwave absorption technique was used to measure the electrical conductivity of these Cu particles. Under differential reaction conditions at 423 K and 1 atm, all catalysts exhibited deactivation on stream and activities were typically 10−20% of their initial values after 3−4 h on stream. However, initial turnover frequencies (TOFs) varied from 0.056 s-1 on the most highly dispersed Cu catalyst to 0.50 s-1 on Cu powder, with the highest TOF of 2.4 s-1 occurring on 110 nm crystallites. A similar trend with a broader (80-fold) variation was observed in the “steady-state” TOF values. Apparent activation energies varied between 11 and 14 kcal/mol. These initial TOF values are in good agreement with previous results, and a correlation exists between TOF and Cu cry...