Synergistic catalysis by Mn promoted ceria for molecular oxygen assisted epoxidation

Mesoporous manganese doped cerium oxide catalysts were prepared by an inverse micelle method with different manganese loadings. These materials exhibited superior activity for epoxidation of alkenes with molecular oxygen. Highest active 10MnCe material showed an activity of 80 % conversion and > 99 % selectivity for cyclooctene epoxidation. The fluorite crystal structure which facilitates the high oxygen mobility, low tem-perature reducibility, homogeneous distribution of manganese on ceria, nanoparticle nature, higher number of oxygen vacancies, low valent states of manganese and cerium, and the ability to generate reactive oxygen species of the manganese doped cerium oxide could be correlated to the high catalytic activity. The reaction followed first order kinetics with a rate constant of 0.31 h(-1) at 100 degrees C, and the activation energy turned out to be 10.5 kJ/ mol. The mechanistic study revealed that the reaction proceeds via a unique mechanism which involves in situ generated superoxide and singlet oxygen species.