Effects of tungstate and phosphate species on the acidity of ZrO2-TiO2 solid acids

• Main Authors: Shen, Po-Fan, 沈柏汎
• Other Authors: Chang, Sue-Min
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/50639041136011908784

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 600C. 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.