| Summary: | 碩士 === 國立臺灣大學 === 化學工程學研究所 === 94 === Abstract
In the present study we focused on the dehydrogenation and oxidative dehydrogenation of propane over Pt-Sn/BN catalysts with various Sn loadings which were prepared by co-incipient wetness impregnation. We also prepared monometallic catalysts 1.1wt%Pt/BN and 1.0wt%Sn/BN for comparison. A commercial catalyst support γ-Al2O3 was chosen to compare with BN. Several characterization techniques were used including BET surface area measurement by N2 adsorption, hydrogen selective chemisorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscope (TEM). From the XPS analysis, most of tin remained Sn2+ after H2 reduction at 400oC. PtxSn alloys were formed due to partially reduced Sn in Pt-Sn/BN. Furthermore, the crystalline phases of PtSn and SnPt3 alloys were also observed from the XRD spectra of Pt-Sn/BN catalysts. However PtxSn alloys were not detected in Pt-Sn/γ-Al2O3 by XRD. The reaction results at 600℃ revealed that the tin addition clearly improved the activity and lifetime of Pt/BN. The more tin in Pt-Sn/BN, the higher the selectivity and yield to propylene were. After six-hour reaction, a maximum yield of propylene (25.3%) was maintained using Pt-Sn(0.75wt%)/BN catalyst with the poorest Pt dispersion (0.67%) in all of Pt-Sn/BN catalysts. The Pt dispersion of Pt-Sn(0.75wt%)/BN was much smaller than that of Pt-Sn(0.50wt%)/γ-Al2O3. However, the yield of propylene on Pt-Sn(0.75wt%)/BN was almost equal to Pt-Sn (0.50wt%)/ γ-Al2O3 (propylene yield 29.5%). We suggest that the electropositive metal B (Sn) on Pt-Sn/BN acts as an electron-donor increasing the electron density on metal A (Pt), thus depresses the C=C (alkene) binding energy, then enhances the catalytic activity, propylene selectivity and lifetime. Furthermore, the catalysts of γ-Al2O3 were deactivated rapidly in the oxidative dehydrogenation of propane. We were speculating that active sites were blocked by the formation of H2O during reaction, thus decreasing activity. Consequently, not only the nature of supports and Pt dispersion, but also PtxSn alloys and crystalline phases of PtSn on the BN-supported affected the performance of catalysts for propane
dehydrogenation and oxidative dehydrogenation.
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