Catalysis in flow: O2 effect on the catalytic activity of Ru(OH)x/γ-Al2O3 during the aerobic oxidation of an alcohol

Abstract

Changes in the turnover frequency (TOF) of Ru(OH)_x/γ-Al₂O₃ during aerobic oxidation of benzyl alcohol in a plug flow differential reactor were monitored online using an inline FTIR instrument over extended periods of time (up to 72 h). A new equation for catalyst deactivation is derived, to account for the different lengths of time the catalyst is exposed to the reactants (benzyl alcohol and O₂). Catalyst activity and stability are dependent on the amount of O₂ in the system; catalyst deactivation can be attributed to two simultaneous processes: a fast and reversible inhibition by the benzoic acid side product and a slower and irreversible loss of catalytic sites due to reduction of Ru. At steady state, the reaction rate is zero-order in benzyl alcohol and partial positive order in O₂. Finally, the suitability of a packed-bed (integral) reactor for the reaction is discussed.