| In this work, the loading of nano-sized gold on the surface of HAP with high surface areas is expected to increase the gold dispersion, thus effectively avoiding the possible sintering phenomena during the calcination processes. While different types of Co-Mn oxides were investigated as catalysts for complete oxidation of HCHO at low temperature, a novel "storage-oxidation" cycling process was applied to remove HCHO based on a three-dimensional (3D) ordered cubic mesoporous Co-Mn oxide catalyst. While a novel cyclic process for simultaneous removal of formaldehyde and benzene is proposed over Pt/HZ catalyst and PtAg non-alloy bimetal loaded on nanoscale HZSM-5zeolite. The results were summarized as follows:(1) Hydroxyapatite as a green and abundant material was found to enhance the stabilization of gold nanoparticles against sintering. The origins of such stabilization of HAP on supported gold nanoparticles was investigated in the present study. Phosphate groups interacted and stabilized nano-gold at lower temperature (≤400℃), while hydroxyl group contributed to the stabilization at higher temperature (≤600±℃). Both of them contributed to the strong sintering-resistant for calcination as high as600℃. For the first time we found that Au/HAP and Au/CeO2/HAP catalysts are highly active and stable for HCHO oxidation at room temperature.(2) MnxCo3-xO4solid solution was synthesized by co-precipitation method and tested for the first time for oxidation of HCHO. The formation of MnxCo3-xO4solid solution was confirmed by XRD, H2-TPR, XPS studies. It was observed that complete conversion of HCHO occurred at75℃(GHSV=60,000h-1, relative humidity=50%(25℃)), and remained unchanged within50hours. Such high activity can be ascribed to the large amount of surface oxygen available on MnxCo3-xO4. According to the results of in situ DRIFTs, we proposed a reaction pathway for HCHO oxidation over MnxCo3-xO4catalyst. The influence of moisture on the activity and stability of Mno.75Co2.25O4catalyst for HCHO and CO oxidation was compared and investigated. Totally opposite effects of relative humidity (RH) on the reactions were observed:with increase of RH (0-90%), the activity for HCHO oxidation was enhanced, whereas the activity for CO oxidation was greatly decreased. However, in both cases the catalyst lifetime was prolonged in the presence of moisture (RH=50%). Such modifications were directly evidenced by correlating in梥itu DRIFTS data, TPO results and MS-IRAS studies, which clarified the effects of water on the activity and stability of Mno.75C02.25O4catalyst for HCHO and CO oxidation. (3) Three-dimensional (3D) ordered cubic mesoporous Co-Mn oxide (denoted as CoMn-HT) was fabricated using a KIT-6-templating strategy and was tested in a "storage-oxidation" cycling process for the removal of formaldehyde. The formation of a3D ordered mesoporous structure was confirmed by low-angle XRD, nitrogen adsorption-desorption data, and TEM micrographs. The CoMn-HT catalyst showed promising properties in both the storage and regeneration phases, and remained active in highly humid air (RH=90%) and at high GHSV (160,000h-1).(4) A novel cyclic process for simultaneous removal of formaldehyde and benzene is proposed, incorporating the use of a zeolite-supported noble metal catalyst, n principle, such a catalyst should have sites for benzene storage (HZSM5zeolites) and sites for formaldehyde and benzene oxidation (noble metals). Therefore, HZSM5supported Pt, Pd and Ag catalysts were prepared and their catalytic behaviors for formaldehyde oxidation at room temperature, benzene storage at room temperature, and oxidation of the stored benzene at elevated temperatures were evaluated. The influence of moisture on these processes was also clarified. Pt/HZ catalyst was found to be suitable for the proposed cycling process, good carbon balances being obtained for each cycle without the production of secondary pollutants. A novel cyclic process for simultaneous removal of formaldehyde and benzene over a compositional series of PtAg non-alloy bimetal catalysts supported on nanoscale and microscale HZSM-5was investigated. TEM revealed nanoscale HZSM-5was a better support than the microscale one, which improved the metal dispersion. XRD and XPS showed that there is no evident PtAg alloy formation under the synthesis conditions used. Benzene-TPD results implied the loading of Ag changed the adsorption of HZSM-5significantly, which inhibit the microscale HZSM-5but enhanced the nanoscale HZSM-5. Performance for formaldehyde oxidation and benzene storage at room temperature, oxidation and release of the stored-benzene at elevated temperatures was studied. PtxAg1-x (0.5<x<1) supported on nanoscale HZSM-5catalysts were found to be suitable for the proposed cycling process, good carbon balances being obtained for each cycle without the production of secondary pollutants. |
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