Removal of formaldehyde over MnxCe1 − xO2 catalysts: Thermal catalytic oxidation versus ozone catalytic oxidation

MnxCe1 − 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 5 wt.% CuOx into Mn0.5Ce0.5O2. With ozone catalytic oxidation, HCHO (61 ppm) in gas stream was completely oxidized by adding 506 ppm O3 over Mn0.5Ce0.5O2 catalyst with a GHSV (gas hourly space velocity) of 10,000 hr− 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 (Mn0.5Ce0.5O2) 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 10,000 hr− 1, [O3]/[HCHO] = 3 and temperature of 25°C, a high HCHO removal efficiency (≥ 81.2%) was maintained throughout the durability test of 80 hr, indicating the long-term stability of the catalyst for HCHO removal.