Catalytic properties of Ce-MCM-41 prepared with ceric ammonium nitrate in the liquid-phase oxidation of benzyl alcohol

Abstract

This work reports the influence of microstructural features in the catalytic performance, reaction kinetics and stability of a cerium-modified MCM-41 material prepared with ceric ammonium nitrate (Ce-MCM-CAN) in the liquid-phase oxidation of benzyl alcohol with tert-butyl hydroperoxide (TBHP) as oxidant. All the mentioned features were compiled and compared to other two Ce-MCM-41 catalysts prepared with CeCl3·7H2O and Ce(NO3)3·6H2O (Ce-MCM-Cl and Ce-MCM-NO3, respectively). Ce-MCM-CAN sample has offered a unique catalytic profile and considerable resistance towards conversion of isomorphous cerium sites in inactive agglomerated CeO2. In a typical catalytic essay at 80 °C and 24 h, Ce-MCM-CAN sample attains 54.6% of conversion, with 47.4 and 25.9% of benzaldehyde selectivity and yield, respectively. Nonetheless, kinetic essays demonstrates that the reaction continues after 24 h, mainly by reducing the aldehyde's selectivity and favoring the formation of benzoic acid, whereas Ce-MCM-Cl and Ce-MCM-NO3 samples has product formation stagnated after 20 h. After four catalytic cycles, the deactivation of Ce-MCM-CAN sample occurs mainly after the first cycle (reduction of 19.8% in conversion) with little influence in TBHP efficiency, while the other two model catalysts deactivate progressively after each cycle (reduction of 33.3 and 23.6% in conversion for Ce-MCM-Cl and Ce-MCM-NO3 samples, respectively) with loss of oxidant usage. Overall, the long-range ordering and pre-existing non-framework CeO2 nanoparticles in Ce-MCM-CAN sample is responsible for decreasing the deactivation rate. Such properties emerge from the counterbalanced synergy between chaotropic nitrate anions and condensation between [Ce(OH)4] species with silicate anions.