| Volatile organic compounds (VOCs) are liquid or solid materials containing carbon, such as fat, aromatic hydrocarbons, ketones, alcohols, halogenated hydrocarbons, aldehydes, ethers, epoxy compounds and phenolic compounds. Among these harmful substances, toluene is a refractory gas at room temperature. Therefore, the study of toluene removal has become a hot topic in recent years. However, now the required temperature is often higher for complete degradation of toluene, so the methods are not conducive to the actual application. This paper mainly studies the use of transition metal oxide Co3O4with a special structure for catalytic oxidation of gaseous toluene. The main investigations carried out are as follows:1. CoO4nanorods were fabricated by a low-temperature hydrothermal method by adding a small amount of surfactant (polyvinylpyrrolidone, PVP). In the experiment process the samples aged at95℃. By changing the aging time and pH of the solution, we study the influence of these two factors on the Co3O4nanostructures. The results of X-ray diffraction (XRD) and transmission electron microscopy (TEM) suggested the obtained samples were cubic crystal Co3O4nanorods. The result of hydrogen temperature programmed reduction (H2-TPR) and N2adsorption and desorption showed the difference of the aging time and pH can affect the Co3O4nanorods size, pore structure, and then affect the particle of its surface area. Using toluene as the target gas, we study the catalytic properties of Co3O4with gas chromatography (GC) testing. The results showed that the regulation of aging time and pH during the preparing process of Co3O4nanorods affected only the low-temperature degradation. When the temperature was lower than260℃, the best activity of the catalyst is pH=9and the aging time of12h; When temperature was higher than260℃, the three degradation curves were basically the same.2. Co3O4nanoflower clusters were fabricated by a simple low-temperature hydrothermal method. XRD, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), TEM, H2-TPR, the UV-vis diffuse reflectance spectrum (DRS), Raman spectroscopy, electronic paramagnetic resonance (EPR) and X-ray photoelectron spectra (XPS) were employed to characterize the Co3O4nanomaterials. The self-assembled Co3O4nanoflower clusters had good crystallinity and porous structure. They were utilized as the catalyst for the degradation of gaseous toluene. The experimental results showed that the catalytic activity of the as-prepared Co3O4nanoflowers clusters was much superior to the Co3O4blocks under the same reaction condition.3. Ag-Co3O4nanomaterials were prepared by traditional impregnation using Co3O4nanoflower clusters as support. Ag was found successfully loaded on the catalyst surface according to the results of XRD and XPS characterization, and even distributed well on the surface. By comparing the catalysts before and after Ag loading for degrading toluene, we found that its catalytic activity has been significantly improved with Ag loading. Compared with the temperature of toluene completely degrading, Ag-Co3O4nanomaterials is superior to the catalyst CO3O4nanoflower clusters.4. The in situ FTIR was used to study the mechanisms of the reaction and adsorption process of toluene over the as-prepared catalysts. We preliminarily concluded that the mode of adsorption was parallel adsorption by analyzing the adsorption process. The IR results of reaction process showed that the main intermediate products were benzaldehyde and benzoic acid during the reaction process. Different mechanisms of adsorption were determined for the catalysts before and after loading Ag. |
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