Experimental study and kinetic model analysis on photothermal catalysis of formaldehyde by manganese and cerium based catalytic materials.

Abstract

Modern people spend more and more time in cars in their daily lives, and the pollution of formaldehyde in the car may directly affect people's health. Thermal catalytic oxidation technology by solar light is a potential way to purify formaldehyde in cars. MnO_x-CeO₂ was prepared by the modified co-precipitation method as the main catalyst, and the basic characteristic (SEM, N₂ adsorption, H₂-TPR, UV-visible absorbance) were also analyzed in detail. The experimental study was set up to simulate the solar photothermal catalysis of formaldehyde in-car environment. The results showed that the higher the temperature in the experimental box (56.7 ± 0.2°C, 62.6 ± 0.2°C, 68.2 ± 0.2°C), the better the formaldehyde degradation by catalytic effect (formaldehyde degradation percentage: 76.2$\%$, 78.3$\%$, 82.1$\%$). With increase of the initial formaldehyde concentration (200 $ppb$, 500 $ppb$, 1000 $ppb$), the catalytic effect first increased and then decreased (formaldehyde degradation percentage: 63$\%$, 78.3$\%$, 70.6$\%$). The catalytic effect risen gradually with the increase of load ratio (10$g/m^2$, 20$g/m^2$, and 40$g/m^2$), and the formaldehyde degradation percentages were 62.8$\%$, 78.3$\%$, and 81.1$\%$, respectively. According to the expressions of the Eley-Rideal (ER) model, the Langmuir-Hinshelwood (LH) model, and the Mars-Van Krevelen (MVK) model, the experimental results were fitted and verified, and it was found that the ER model had a high degree of fit. It is more suitable to explain the catalytic mechanism of formaldehyde by MnO_x-CeO₂ catalyst in the experimental cabin, where formaldehyde is in the adsorption state and oxygen is in the gas phase.Implications: Judging from the current research status, vehicles have become an indispensable mode of travel for people, and the air quality in the vehicle is not optimistic. Most vehicles generally have the phenomenon of excessive formaldehyde. The characteristic of formaldehyde in the car is the continuous release, especially in the hot summer, the temperature inside the car rises sharply under the sun radiation. At this time, the formaldehyde concentration exceeds the standard by 4 to 5 times, which can cause great damage to the health of the passengers. In order to improve the air quality in the car, it is necessary to adopt the correct purification technology to degrade formaldehyde. The problem brought by this situation is how to effectively use solar radiation and high temperature in the car to degrade formaldehyde in the car. Therefore, this study uses the thermal catalytic oxidation technology to catalyze the degradation of formaldehyde in the high temperature environment of the car in summer. The selected catalyst is MnO_x-CeO₂, mainly because manganese oxide (MnO_x) itself is the most effective catalyst for volatile organic compounds (TCO) among transition metal oxides, and CeO₂ has excellent oxygen storage and release capacity and Oxidation activity, which helps to improve the activity of MnO_x. Finally, the effects of temperature, initial concentration of formaldehyde and catalyst loading on the experiment were explored, and the kinetic model of thermal catalytic oxidation of formaldehyde with MnO_x-CeO₂ catalyst was analyzed to provide technical support for the future application of this research in practice.