Selective oxidation of aromatic alcohols over amorphous Mn-Ce-O catalyst

A series of Mn-Ce-O catalyst samples with different Mn/Ce molar ratios were synthesized by a redox-precipitation method. The catalytic performance of Mn-Ce-O for the selective oxidation of various aromatic alcohols to corresponding aldehydes or ketones with molecular oxygen as an oxidant in liquid phase was studied. The catalytic activity of Mn-Ce-O with Mn/Ce molar ratio of 10 was the highest, and the benzyl alcohol conversion was 96.6% with the mass specific activity of 19.3 mmol/(g-h) at 100°C in 1h. The catalyst could be recycled up to six runs without appreciable loss of its activity. X-ray diffraction, nitrogen physisorption, X-ray absorption spectroscopy, and hydrogen temperature-programmed reduction were used to characterize the Mn-Ce-O catalyst. The key active component for the O₂ activation was the amorphous MnO_x with coexistence of Mn³⁺ and Mn⁴⁺. The addition of highly dispersed CeO_x to the amorphous MnO_x played an important role in catalytic performance of the Mn-Ce-O catalyst, increasing its BET surface area, promoting the reduction of MnO_x, increasing the capacity of surface oxygen reproduction of MnO_x, and thus remarkably enhancing the catalytic activity and the recycling capability.