Removal of formaldehyde over Mn_xCe_1-xO₂ catalysts: Thermal catalytic oxidation versus ozone catalytic oxidation

Mn_xCe_1-xO₂ (x: 0.3-0.9) prepared by Pechini method was used as a catalyst for the thermal catalytic oxidation of formaldehyde (HCHO). At x=0.3 and 0.5, most of the manganese was incorporated in the fluorite structure of CeO₂ to form a solid solution. The catalytic activity was best at x=0.5, at which the temperature of 100% removal rate is the lowest (270°C). The temperature for 100% removal of HCHO oxidation is reduced by approximately 40°C by loading 5wt.% CuO_x into Mn_0.5Ce_0.5O₂. With ozone catalytic oxidation, HCHO (61ppm) in gas stream was completely oxidized by adding 506ppm O₃ over Mn_0.5Ce_0.5O₂ catalyst with a GHSV (gas hourly space velocity) of 10,000hr^-1 at 25°C. The effect of the molar ratio of O₃ to HCHO was also investigated. As O₃/HCHO ratio was increased from 3 to 8, the removal efficiency of HCHO was increased from 83.3% to 100%. With O₃/HCHO ratio of 8, the mineralization efficiency of HCHO to CO₂ was 86.1%. At 25°C, the p-type oxide semiconductor (Mn_0.5Ce_0.5O₂) exhibited an excellent ozone decomposition efficiency of 99.2%, which significantly exceeded that of n-type oxide semiconductors such as TiO₂, which had a low ozone decomposition efficiency (9.81%). At a GHSV of 10,000hr^-1, [O₃]/[HCHO]=3 and temperature of 25°C, a high HCHO removal efficiency (≥81.2%) was maintained throughout the durability test of 80hr, indicating the long-term stability of the catalyst for HCHO removal.