Aerobic Oxidative Dehydrogenation of Ethyl Lactate Over Reduced MoVNbO x Catalysts

The present study investigated the effect of low-valent transition metal ions and oxygen vacancies on the catalytic selective oxidation properties over reduced MoVNbO x catalysts. The MoVNbO x -catalyzed synthesis of ethyl pyruvate (EP) from ethyl lactate (EL) using molecular oxygen (O 2 ) as the hydrogen acceptor under mild aerobic and normal pressure conditions is described. It was found that the nitrogen (N 2 ) calcined catalysts with low-valent metal ions (V 4+ and Mo 4+ ) increased the oxidative dehydrogenation (ODH) reaction rate and the EL conversion reached 90.6% (~ 21.1 mmol [EP] mmol [V 4+ ] −1 h −1 ). The ODH catalytic activity of the N 2 –MoVNbO x catalyst was four times higher than that of the pristine MoVNbO x catalyst. Low-valent V 4+ ions introduced plenty of oxygen vacancies to the surface structure and increased the oxygen mobility, which facilitated the ODH reaction. Together, the results of the temperature programmed reduction of hydrogen (H 2 -TPR), X-ray photoelectron spectroscopy (XPS) and ODH reaction experiments revealed that the presence of low-valent V 4+ /Mo 4+ ions not only lowers the reduction temperature of oxide catalysts, but also facilitates the capture of O 2 on the site of oxygen vacancies. The presence of active sites of low-valent V 4+ ions and oxygen vacancies was proposed as the reaction mechanism responsible for the high activity. These results have implications for our understanding of the effects of oxidation processes on reduced multi-component oxides. Graphical Abstract