Pd/TiO2 catalysts prepared by electroless deposition with and without SnCl2 sensitization for the liquid-phase hydrogenation of 3-hexyn-1-ol
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Pd/TiO2 catalysts were prepared by the electroless deposition method with and without SnCl2 sensitization and employed in the liquid-phase selective hydrogenation of 3-hexyn-1-ol under mild conditions (40 °C, H2 0.2 MPa). As revealed by inductively coupled plasma optical emission spectroscopy, transmission electron microscopy, and CO pulse chemisorption, the use of conventional SnCl2/PdCl2 solution resulted in a larger amount of Pd being deposited (0.98 wt% Pd) on the TiO2 and higher Pd dispersion (6.6 × 1017 molecules CO/g Pd) than the SnCl2-free activation (0.87 wt% Pd, 5.3 × 1017 molecules CO/g Pd). However, tin was found to remain on the catalyst in the form of Sn4+ and partially covered the Pd surface. Large Pd particles were formed after electroless plating of Pd when the TiO2 was activated by PdCl2 followed by the reduction using NaH2PO2 (SnCl2-free process). The selectivity towards cis-hexen-1-ol after complete conversion of 3-hexyne-1-ol was much improved using the electroless deposition catalysts (selectivity 60–87 %) compared to the ones prepared by conventional impregnation method (selectivity 4 %). The results in this study show the advantages of electroless deposition technique as a simple methodology to synthesize highly selective catalysts for the production of cis-alkene in the alkynes semihydrogenation.
KeywordsSelective hydrogenation 3-hexyn-1-ol Electroless deposition Pd catalyst Sn sensitization
Financial supports from the Thailand Research Fund (TRF), the Office of Higher Education Commission (CHE), and the NRU-CU are gratefully acknowledged. The authors also acknowledge supports from Chulalongkorn University under Special Task Force for Activating Research (STAR) project granted to the Metallic Surface Coating Technology for Corrosion Protection (MCTC) research group and the National Research Council of Thailand (NRCT) for the NRCT-JSPS Joint Research Program.
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