| Summary: | 碩士 === 國立交通大學 === 環境工程系所 === 103 === Owing to the low electronegtivity of Zr4+ and Ti4+ ions, a porous ZrO2-TiO2 composite was prepared using a templating method and was further modified with tungstate and phosphate species, which contain high electrongativity centers, through incorporation or impregnation method to increase the surface aidity. The substrate exhibited a high surface area of 195 m2/g with a pore size of 6.3 nm. The quantity of the acidic sites was 859 µmol/g. Because of the great solubility of the ZrO2 in the TiO2 matrix, crystallization is inhibited and the porous structure is stabilized till 600C. Rather than impregnation, incorporation of the two modifiers enhanced the surface acidity to a higher degree. The incorporated phosphate and tungstate species increased the number of the acidic sites to 1,547 and 972 µmole/g, respectively. The optimal P/M and W/M raito which leads to the highest acidity was 0.44 and 0.16, respectively. The W6+ ions with a high coordination number and electronegativity within the surface lattice resulted in oxygen vacancies and strong Lewis acid sites. On the other hand, P5+ ions led to Bronsted acidity because their low coordination number creates substaintial anounts of hydroxyl groups on the Ti4+ or Zr4+ centers. Compared to the WO3 moieties, PO43- species is more capable of stabilizing the microstructure of the substrate to aginast thermally induced transformation. Therefore, the incorporated phospahe speices increased the surface area to 270 m2/g and maintained the small pore size of 3.5 nm. The repeated NH3-TPD test indicated that the modified solid acid peformed high recoverability. In addition, its acid amount and density was higher than those of the commercial zeolite, suggesting the phosphated ZrO2-TiO2 solid acids a promising adsorbent for removal of base gases.
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