Synergism between Manganese and Cobalt on Mn-Co Oxides for the Catalytic Combustion of VOCs: A Combined Kinetics and Diffuse Reflectance Infrared Fourier Transform Spectroscopy Study

Binary Mn-Co oxides were prepared by means of homogeneous coprecipitation with various Mn/Co molar ratios to investigate the effect of interaction between manganese and cobalt on the catalytic combustion of volatile organic compounds (VOCs). It was found that the catalytic activities of Mn-Co oxides for VOC combustion were higher than that of monometallic oxides (MnOx or CoOx), showing a synergistic effect. Kinetic studies showed that the catalytic activity was highly dependent on the property of oxygen and the reaction pathway followed the Mars-van Krevelen (MvK) mechanism with oxygen in dissociative adsorption. Temperature-programed reduction with H-2 and X-ray photoelectron spectroscopy results illustrated that the interaction between manganese and cobalt resulted in a higher concentration of Mn4+/Mn3+ and Co2+/Co3+ redox pairs, which favored the formation of active oxygen species and oxygen mobility and thus enhanced the catalytic activity. Moreover, the Mn1Co1Ox catalyst exhibited high stability in the presence of water vapor. Furthermore, diffuse reflectance infrared Fourier transform spectroscopy results indicated that toluene reacted with the oxygen of the catalyst to generate benzyl, benzyl alcohol, and benzoate species in consecutive steps. Finally, the benzoate species were fully oxidized to CO2 and H2O, which was the rate-determining step for the catalytic combustion of VOCs. These results provided a guideline for the future development of superior catalysts via regulating synergism among distinct metals for the catalytic removal of VOCs.