Aerobic Oxidative Dehydrogenation of Ethyl Lactate Over Reduced MoVNbOx Catalysts

Abstract

The present study investigated the effect of low-valent transition metal ions and oxygen vacancies on the catalytic selective oxidation properties over reduced MoVNbOx catalysts. The MoVNbOx-catalyzed synthesis of ethyl pyruvate (EP) from ethyl lactate (EL) using molecular oxygen (O2) as the hydrogen acceptor under mild aerobic and normal pressure conditions is described. It was found that the nitrogen (N2) calcined catalysts with low-valent metal ions (V4+ and Mo4+) increased the oxidative dehydrogenation (ODH) reaction rate and the EL conversion reached 90.6% (~ 21.1 mmol [EP] mmol [V4+]−1 h−1). The ODH catalytic activity of the N2–MoVNbOx catalyst was four times higher than that of the pristine MoVNbOx catalyst. Low-valent V4+ 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 (H2-TPR), X-ray photoelectron spectroscopy (XPS) and ODH reaction experiments revealed that the presence of low-valent V4+/Mo4+ ions not only lowers the reduction temperature of oxide catalysts, but also facilitates the capture of O2 on the site of oxygen vacancies. The presence of active sites of low-valent V4+ 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.