A Novel Approach Of Plasma Catalysis And Ozone Catalytic Oxidation For Formaldehyde Removal

Formaldehyde is the most common volatile organic compounds in indoor air and may cause serious health disorders for human beings. In this paper, cycled storage-discharge (CSD) plasma catalytic process was applied to low-concentration formaldehyde removal from air. Moreover, in order to clarify the contribution of O3in the CSD plasma catalytic process, ozone catalytic oxidation formaldehyde and its mechanism were studied. The results were as follows:1. Low-concentration formaldehyde removal from air using a CSD plasma catalytic processA CSD plasma catalytic process was used for low-concentration formaldehyde removal from air. The performances of formaldehyde storage and plasma catalytic oxidation of stored formaldehyde on metal or metal oxides loaded HZSM-5(HZ, SiO2/Al2O3=360) catalysts were investigated in simulated air containing low-concentration formaldehyde. For HCHO storage, AgCu/HZ catalysts exhibited preferential storage of HCHO in humid air, and the breakthrough capacity of formaldehyde on AgCu/HZ was four times as large as HZ. HCHO breakthrough capacity of AgCu/HZ catalysts kept almost constant over a wide range of RH (from20%to93%). The breakthrough time of AgCu/HZ catalysts increased approximately in inverse proportion to HCHO concentration even in humid gas streams. At the discharge stage, Ag and Cu in AgCu/HZ catalysts exhibited positive synergistic effect towards complete oxidation of HCHO. The discharge period was almost irrelevant to the storage period. Air can be used as a discharge gas for complete oxidation of HCHO, and stored HCHO inhibited the formation of nitrogen oxides.Large breakthrough capacity of AgCu/HZ towards formaldehyde may lead to lowering energy cost of this CSD plasma catalytic process. Taking the case of purifying simulated air containing6ppm of HCHO with50%and600ml min-1as an example, the energy cost of the CSD plasma catalytic process was1.9×10-3kWh/m3-air.2. Ozone catalytic oxidation of formaldehyde in air at room temperatureOzone catalytic oxidation (OZCO) of formaldehyde in air was studied at room temperature. For simulated air containing103ppm HCHO with56%RH, formaldehyde could be totally oxidized to CO2and H2O by300ppm O3over MnOx catalysts at GHSV (gas hourly space velocity) of2×105h-1. Water vapor showed a significantly enhanced effect on OZCO of HCHO to CO2. No byproduct was detected during HCHO oxidation with O3over the MnOx catalysts using an online Fourier transform infrared spectrometer.3. The mechanism of ozone catalytic oxidation of formaldehydeIn order to better understand the accumulation and the removal of surface species on MnOx catalysts during OZCO of formaldehyde, in-situ diffuse reflectance infrared Fourier transform (DRIFT) spectra studies were investigated. In-situ DRIFT spectra demonstrate that the amount of both monodentate and bidentate carbonate species on MnOx, in the dry stream, increased gradually with time on stream (TOS). However, in the humid stream, almost no accumulation of carbonate species on the catalysts was observed.To clarify the reaction pathways for OZCO of HCHO, and the enhanced effect of water vapor on complete oxidation of formaldehyde and the reaction stability over MnOx catalysts, HCHO surface reaction and CO2adsorption/desorption experiments on the fresh, O3and O3+H2O treated MnOx catalysts were examined comparatively...