HCHO Removal by MnO₂(<i>x</i>)–CeO₂: Influence of the Synergistic Effect on the Catalytic Activity

Abstract

The catalytic performance of MnO2(x)–CeO2 (x = Mn/Ce molar ratio) and the synergistic effect have been investigated in formaldehyde removal. The results showed that formaldehyde achieved 100% conversion at 60 °C for MnO2(1.5)–CeO2, with the gas hourly space velocity = 120 000 mL h–1 gcat–1. It was lower than the formaldehyde removal temperature of MnO2 (130 °C) and CeO2 (170 °C). The apparent activation energy for HCHO oxidation with MnO2(1.5)–CeO2 was 34.2 kJ mol–1. The partial mutual replacement of Mnx+ and Cex+ decreases the crystallite size due to the MnO2/CeO2 interaction. The X-ray photoelectron spectroscopy and the Raman analyses show that the Mn3+/Mn and Oads/Olatt ratios and the relative concentrations of oxygen vacancies for MnO2(1)–CeO2 and MnO2(1.5)–CeO2 were higher than those of the rest of the catalysts. Thus, the lattice oxygen (Olatt) from CeO2 readily transfers to the oxygen vacancy, achieving Olatt activation to surface-adsorbed oxygen (Oads).