Complete catalytic oxidation of ethanol over MnO2 with different crystal phase structures

Abstract

α-MnO2, β-MnO2, γ-MnO2, and δ-MnO2 catalysts were synthesized by hydrothermal methods, and their catalytic performances towards the oxidation of ethanol were evaluated in detail. The as-synthesized MnO2 catalysts were characterized by N2 adsorption-desorption measurements, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and H2 temperature-programmed reduction (H2-TPR). The α-MnO2 catalyst showed the best activity of the catalysts tested for the combustion of ethanol and the trend in the activity of different MnO2 catalysts towards the oxidation of ethanol was of the order α-MnO2>δ-MnO2>γ-MnO2>β-MnO2. The effect of the crystal phase structure on the activity of the MnO2 catalysts was investigated. The XRD results showed that there were differences in the crystallinities of the α-, β-, γ-, δ-MnO2 catalysts, but these differences did not have a significant effect on their catalytic performances towards the oxidation of ethanol. The BET surface areas of the α-, β-, γ-, δ-MnO2 catalysts exhibited similar tendencies to their ethanol oxidation activities, although the results of standardization calculations showed that the surface area was not the main factor affecting their catalytical activities. The XPS results showed that the lattice oxygen concentration played an important role in defining the catalytic performance of the MnO2. The α-MnO2 catalyst showed the best reducibility of all of the MnO2 catalysts tested, as determined by H2-TPR. The excellent performance of α-MnO2 was attributed to its higher lattice oxygen concentration and reducibility, which were identified as the main factors affecting the activity of the MnO2 towards the complete oxidation of ethanol.