Catalytic oxidization of indoor formaldehyde at room temperature - Effect of operation conditions

Catalytic oxidization has been studied for elimination of formaldehyde, which is a common and toxic indoor pollutant. However, most of previous studies were conducted at temperature and concentration level much higher than typical room condition. The current paper is to determine the effectiveness of catalytic oxidization of formaldehyde at room condition. The performance of one noble metal catalyst (Pd/γ-Al₂O₃) and two transition metal oxide catalysts (Fe₂O₃-MnO₂ and CuO-MnO₂) were studied at room temperature (23-25°C). The effect of concentration (0.5-5ppm), relative humidity (20-80%) and air velocity (0.2-1.0m/s) were studied with single-pass breakthrough method. The major conclusions are: (1) Under room temperature and much lower concentration levels than in previous studies, the noble metal catalyst also demonstrated significantly better removal performance than metal oxide, maintaining a constant efficiency with time; (2) For different concentration levels, the efficiency of Pd/γ-Al₂O₃ did not change significantly at concentrations below 5ppm, while the efficiency increased as concentration decreased for Fe₂O₃-MnO₂; (3) the effect of relative humidity on the catalysts performance was not consistent for different type of catalysts; (4) Regarding the mass transfer mechanism, the importance of external mass transfer process was revealed by tests at different velocity for surface coated catalyst and dimensionless analysis, while both internal diffusion and external mass transfer are influential for homogeneously formed catalyst pellet. (5) The effect of multi-pollutants existence was also investigated, and it was found that the presence of other VOCs slightly decrease the performance of Pd/γ-Al₂O₃, but not Fe₂O₃-MnO₂.