Generation of abundant defects in Mn-Co mixed oxides by a facile agar-gel method for highly efficient catalysis of total toluene oxidation

A facile agar-gel method was successfully applied to prepare a series of homogenous Mn-Co mixed oxides with different Mn/Co molar ratios for highly efficient catalysis of total toluene oxidation. The obtained Mn2Co1 mixed oxide exhibited a high catalytic activity with excellent durability as well as high tolerability even under 20 vol.% water vapor environment. Characterizations by XRF, XRD, N2 adsorption-desorption, SEM, TEM, H2-TPR, O2-TPD, XPS measurements with density functional theory (DFT) calculations indicated that the obtained optimum Mn-Co mixed oxide had high specific surface area, large amounts of Co3+, Mn3+, and Mn4+ species, abundant adsorbed oxygen species, rich lattice defects, high reducibility at low temperature, and excellent O2 adsorption ability. Meanwhile, in situ DRIFTS spectra measurements confirmed the generated intermediates at different environments during the toluene oxidation and revealed that both adsorbed oxygen and lattice oxygen species could simultaneously participate in the toluene adsorption-oxidation process, especially the rate-controlling step should be the C=C breakage of aromatic ring. It is expected that the present agar-gel method with low cost and convenient operation could be widely applied for the designing of novel mixed metal oxides catalysts for VOCs oxidation.