Cerium modified birnessite-type MnO2 for gaseous formaldehyde oxidation at low temperature

Cerium modified birnessite-type manganese dioxides (Ce-MnO2) with different doping ratios were prepared by a redox reaction of KMnO4 with (NH4)2C2O4 in the presence of Ce(NO3)3. The as-synthesized Ce-MnO2 samples were characterized by XRD, SEM, TEM, BET, XPS, ICP-AES, H2-TPR, Raman and in situ DRIFTS. The results indicate that doping of cerium significantly enhance the performance of birnessite for HCHO removal at low temperature. Ce-MnO2(1:10) with the nominal Ce/Mn ratio of 1:10 exhibited the best activity and achieved complete HCHO conversion at 100 °C and better activity at room temperature than undoped birnessite. Upon the doping of cerium, the growth of MnO2 crystal was inhibited, leading to smaller particle size and higher specific surface. In addition, CeO2 nanocrystal formed even at low doping ratio (0.1:10), resulting in close contact between CeO2 and MnO2 nanocrystals. As a result, the doped material owned higher content of oxygen vacancies and surface adsorbed oxygen species, which contributed to its high activity for HCHO oxidation. This investigation provides a new point of view about how to design an inexpensive efficient catalyst for indoor air purification via introducing appropriate content of cerium.