限制空間內的化學： 超冷水的相變行為研究與中孔洞氧化矽材料負載釩金屬之催化應用

Chemistry in the Confined Space： Study of Phase Transition of Supercooled Water and Catalytic Applications of Mesoporous Vanadiumsilicate

陳佳政(Chia-Cheng Chen)

指導教授 ： 牟中原

國立臺灣大學/理學院/化學研究所/碩士(2008年)

https://doi.org/10.6342/NTU.2008.01314

摘要

許多物質在奈米尺度的限制空間中，其化學反應與物理性質皆迥異於巨觀條件。以傳統方法合成的中孔洞氧化矽材料在進行過冷水的研究時，多半面臨到穩定度低、孔洞性質不易維持的難處。本論文以沸石晶種(zeolite seed)作為矽源，成功合成出具高穩定性、高酸性且孔洞大小可調控至微孔(< 2nm)等級的氧化矽材料；再進一步利用此材料合成出具規則的微孔尺度碳材。
　　將水限制於1.5nm的微孔洞氧化矽材料內，即使降溫至攝氏零下一百度也不會有任何結冰的現象；本論文亦首次利用微孔洞碳材作為超冷水的載體並發現將水限制於1.2nm的孔道內也有相同的不結冰現象。利用低溫式示差掃描熱量分析儀(LT-DSC)來觀測超冷水限制於不同孔徑之規則孔道碳材的熔點變化行為，比較以往氧化矽材料發現有明顯不同。推測是碳材的疏水表面特性造成。也因為碳的表面特性有異於氧化矽材料。本論文所發展的規則孔洞碳材將成為繼中孔洞氧化矽材料之後，一種應用於限制空間規範的新式超冷水載體材料。
本論文亦研究了釩金屬在限制空間內的氧化催化反應，文獻上報導釩金屬對於各種芳香族化合物的氧化具有優異的活性及選擇性。苯酚為工業上大量需要的試劑，其工業製程為異丙苯法。此製程不僅複雜、危險產生且伴隨大量副產物生成，導致成本升高。因此有許多文獻開始研究如何有效率的得到苯酚，較成功的方法為藉由雙氧水氧化過渡金屬產生的Fenton-like自由基電子，可將苯一步氧化為苯酚。我們選擇了不同顆粒大小尺度的中孔洞氧化矽材料(MCM-41)作為載體，附載釩金屬離子作為催化劑；並進一步改變其孔洞大小及表面性質，藉由苯氧化反應的活性及選擇性來探討不同限制空間效應對於苯直接氧化為苯酚的催化反應影響。以便於往後設計出更具有催化活性及選擇性的中孔洞材料催化劑。

關鍵字

中孔洞

並列摘要

Because of the amorphous nature of the pore wall, MCM-41 and MCM-48 have weaker acidity and much less hydrothermal stability than conventional zeolites. This limits their application. In this thesis, we improve the stability of pore structure and acidity by using pre-formed Beta zeolite seeds as silica source. On the other hand, using various hydrophobic chain length of cetyltrimethylammonium bromide (C10~C16TAB), hydrothermal temperature (100℃~150℃), and procedure (once or twice hydrothermal method); we derive hexagonally ordered aluminosilicate (MCM-41-S) with narrow pore size distribution in the super-microporous range (less than 2.0nm ).
Furthermore, the catalytic application of the solid acid catalysts (MCM-48-S) was demonstrated. In the conventional way, mesoporous carbon (CMK-1) was obtained by impregnation of sucrose on MCM-48 followed by dehydration with concentrated sulfuric acid. Because of the strong acidity of MCM-48-S, CMK-1 could be synthesized without sulfuric acid. The synthesized mesoporous carbon has high surface area (~1500 m2/g) smaller pore size (1.2nm). Cramming water molecules into a tiny space, with a diameter less than 1.5nm, allowing water to remain liquid at a much lower temperature ( -100℃). The non-freezing behavior could be seen for ordered porous silica and carbon. We observed doublet meting peak from water confined in porous carbon by LT-DSC, but only one peak in silica substrate. This may come from more hydrophobic surface of carbon than silica.
We also investigate the oxidizing of vanadium catalysts in the confined space. By changing the particle size and pore orderity of mesoporous silica as support. We discovered nano-sized support has faster conversion rate, and higher selectivity for support with ordered pore structure.

並列關鍵字

mesoporous

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