Study Of Assembled Pt Nano-Catalyst For The Complete Oxidation Of Vocs

Volatile organic compounds (VOCs) are released massively by many industrial processes, which could lead to the increase of PM2.5and the haze weather. Low-temperature catalytic oxidation has been considered as an effective and promising method to convert the toxic VOCs into relatively harmless H2O and CO2. In particularly, the supported noble metal catalysts show excellent catalytic performance for elimination of various VOCs, and achieve the goal of effectively purifying air under lower reaction temperature (150-200℃). However, the practical application of this promising technology has been hindered by the lack of high active catalysts with high persistence capability and the short of reaction mechanism for the typical contaminant oxidation process. But developing the higher activity catalyst for complete oxidation of VOCs at lower temperature becomes a major challenge, and a main facing task. To address these issues, this study mainly focused on metal oxides supported platinum catalysts synthesized by direct-adsorption method and wet impregnation method were employed for the catalytic oxidation of toluene and formaldehyde, and systematically investigated a clear relationship between the physicochemical properties of the catalysts and their catalytic oxidative performance. The main research contents and results are as follows: 1. Catalytic performance of toluene oxidation over Pt/TiO2-based catalystsThe catalytic properties of titanium dioxide supported platinum catalysts, prepared by direct-adsorption route and wet impregnation, were investigated for the complete oxidation of volatile organic compounds (VOCs) such as toluene, isopropanol, acetone, and ethyl acetate. As a result, they present in the incoming feed stream (GHSV of18000ml·g-1·h-1) could be completely removed at temperatures below130,135,145, and215℃, respectively, by Pt/γ-Al2O3-AS. It is much better than WI method, even at higher toluene concentrations and space velocity. At the same time, the effect of process conditions towards the oxidation of toluene was also investigated. When the space velocity and the initial concentration increased, VOCs removal rate is reduced. Even so, in the larger range of variety, Pt/TiO2-AS catalyst shows good catalytic performance.But the catalyst shows poor stability in the typical industrial catalytic oxidation process. In order to improve its stability and longevity, we modified by adding additives to enhance oxidation performance of the catalyst. After adding5%K2SO4modification, the stability has dramatically improved, which makes it become a kind of catalyst with wide industrial application prospect. This may due to the strong interaction between K and Pt, which leads to promoted dispersion of the active phase, higher specific surface area, enrichment of surface mobile oxygen species, et al.2. Catalytic performance of HCHO oxidation over Pt/Al2O3-based catalystsAl2O3power, the most common carriers, was adopted to prepare supported Pt-based catalysts by wet impregnation and direct-adsorption methods. The catalytic properties of these Al2O3supported Pt catalysts were investigated for the complete oxidation of formaldehyde. It is found that assembled Pt/Al2O3catalyst synthesized by direct-adsorption method (Pt/Al2O3-AS) shows very high catalytic activity, which could completely oxidize toluene into CO2and H2O at room temperature. According to the results of catalyst characterization, it is indicated that different preparation methods could affect Pt particle’s size and the chemical valence state of the catalyst surface, thus influence on the performance of the catalyst reaction. Compared with Pt/Al2O3-WI catalyst, the Pt/Al2O3-AS catalyst possesses higher ratio of metallic Pt species, which might be a key factor in improving its capability to activate molecular oxygen, thus showing excellent catalytic activity in HCHO oxidation at lower temperature. In addition, the interaction between active component and a large amount hydroxyl groups on the catalyst surface improve the stability of the catalyst.Finally, we put forward the possible reaction mechanism of HCHO total oxidation over Pt/Al2O3-AS. According to the characterization information and results, we find that the assembled catalyst has a lot of surface hydroxyl, which changes the reaction mechanism of room temperature catalytic oxidation of formaldehyde, namely, the direct oxidation mechanism of formate and hydroxyl reaction (HCHOâ†'HCOO-+OHâ†'CO2+H2O).