Novel non-oxide supported Pt catalysts for VOC deep oxidation

• Main Authors: Lin, Chih-An, 林致安
• Other Authors: Jeffery Chi-Sheng Wu
• Format: Others
• Language: zh-TW
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/09309712926149443794

博士 === 國立臺灣大學 === 化學工程學研究所 === 90 === In stead of silica and alumina, the novel non-oxide material was used as the support of deep oxidation catalyst in the research. Activated carbon dispersed Pt and adsorbed reactant well due to its high specific surface area. The activated carbon was pretreated at 400 and 800℃ in nitrogen for 2 hours respectively. Then half of the activated carbons after different thermal pretreatment were soaked in HF for 2 hrs. Higher temperature pretreatment graphitized the surface of activated carbon more, as observed in XPS(X-ray Photon Spectroscopy) and SIMS(Secondary Ion Mass Spectroscopy). The HF pretreatment can lower the ash content on the surface of activated carbon, as proved by EDX(Energy Dispersion X-ray Spectroscopy). The TGA(Thermogravimetric Analysis) and TPD (Temperature-Programmed Desorption) spectra indicated activated carbon can adsorb a huge amount of moisture, aromatics, paraffins, methane and alcohols. The oxygen atom adsorbed on Pt/AC showed higher activity than that adsorbed on Pt/alumina, as proved in TPR spectra. The oxygen atom adsorbed on Pt/AC800 owned the highest activity of those on other Pt/AC catalyst. Pt/AC800 and Pt/AC800HF gave higher activity in benzene and toluene oxidation than Pt/AC400 and Pt/AC400HF due to their higher activity of adsorbed oxygen atoms and higher graphitized surface to adsorb benzene and toluene. Pt/AC400 and Pt/AC400HF displayed better activity in xylene oxidation than Pt/AC800 and Pt/AC800HF. Two extra-methyl groups on xylene was presumed to reduce the adsorption of xylene on the graphitized activated carbon surface. The oxidation activity of Pt/AC was higher than the traditional Pt/alumina catalyst. But, the Pt/AC catalyst decomposed dramatically when we increased the reactant concentration to 2000ppmv. Hexagonal-boron nitride owned high thermal stability, erosion resistance and graphite-like surface structure. The TPR spectra revealed that the Pt particles dispersed on h-BN(hexagonal-boron nitride), especially highly crystallized h-BN, adsorb more active oxygen atoms than Pt particles dispersed on other supports. But, the TPD spectra of Pt/h-BN indicated that Pt/h-BN had lower ability to adsorb organic compound than Pt catalysts supported by other supports. In fact, hexane and methane can not be adsorbed chemically on Pt/h-BN, as revealed in TPD spectra. Pt/h-BN showed high activity in aromatic oxidation. But, it showed similar activity in paraffin oxidation to Pt/alumina. In methane deep oxidation, Pt/alumina is a better catalyst than Pt/h-BN. The VOC reaction order of deep oxidation by Pt/h-BN kept at 1st order. Pt/h-BN can enhance the activity of adsorbed oxygen atoms obviously, but the Pt/h-BN catalyst had low ability to catalyze the organic compound. Therefore, the future work is to find out the promoter for Pt/h-BN to enhance the ability to activate organic compounds.