Pd clusters anchored on grafted TiO2: Genesis and application
| Autor: | Hua-wen Chou, 周樺汶 |
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| Rok vydání: | 2007 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 95 The goal of this research is to develop a new catalyst with high Pd dispersion and longer life-time. A highly dispersed Pd clusters on TiO2 grafted SiO2 (TiO2-SiO2) was prepared by impregnating it with palladium(II) acetate followed with air calcinations and hydrogen reduction. The structures of the grafted TiO2 on SiO2, TiO2-SiO2, were characterized by XRD, EXAFS, and FT-IR. EXAFS reveals that the grafted TiO2 Bwas isolated and Ti was 4 oxygen atoms bonded while FT-IR shows its stronger acidity. The grafted TiO2 promoted anchoring molecular palladium oxides on TiO2-SiO2 through PdOx and TiO2 Binteractions, leading to the formation of subnano Pd clusters. In contrast, Pd clusters on SiO2 and TiO2 prepared under similar conditions shows that Pd2O clusters aggregated during air calcination, resulting in a formation of much larger Pd clusters. The average diameter was about 0.7nm (Pd-Pd first shell coordination number; 6.07) for Pd/TiO2-SiO2 while that for Pd/SiO2 and for Pd/TiO2 was 2nm and 5nm(Pd-Pd first shell coordination number; 8.61 and 10.93). The prepared catalysts were the tested by ethanol partially oxidation and tetralin hydrogenation with sulfur-poisoning reaction. The oxidation reaction was carried out with a continuous fixed bed reactor at 5 atm. and WHSV of 5.0 with temperature ranging from 150 to 200℃. The sulfur-poisoning test were carried out by the hydrogenation of 200 ppm sulfur-containing tetralin at 480 psig, 200℃, and WHSV=12. Both the results show Pd/TiO2-SiO2 exhibits the best catalytic performance among the 3 catalysts. The superior catalytic properties are due to high acidity and strong Pd-TiO2 interactions. The acidity increases the selectivity to ethyl acetate, while supported enhanced by the grafting TiO2 retards aggregation of metal cluster during sulfur-poisoning catalyst deactivation. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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