支撐式奈米碳管觸媒的製備與應用

本論文主要的目標是利用化學氣相沉積法在市售巨觀的二氧化矽球形觸媒擔體(CARIACT 50)表面製備疏水性奈米碳管層之複合材料，並以此新穎材料應用於蜂巢狀催化劑(monolithic catalysts)提升以甲醇生產碳酸二甲酯(dimethyl carbonate, DMC)之氧化羰基化觸媒之穩定性、摻入光觸媒使水分解產生氫氣之應用、作為吸附性材料用於分離溶劑之使用。製備支撐式奈米碳管觸媒的方式，首先藉由微濕含浸法將硝酸鎳水溶液作為鎳觸媒的前驅物含浸至二氧化矽球體上，其鎳含量佔整個擔體的2.5 wt%，接著將真空抽氣乾燥去除溶劑之樣品放入方形高溫爐中，在空氣的氣氛下，以450 °C進行30分鐘鍛燒奈米碳管之觸媒。再將鍛燒完成之樣品放入管狀高溫爐中進行熱化學氣相沉積法生長疏水性奈米碳管層，其中氨氣作為還原氣體、乙炔作為碳源、升降溫區段之環境氣體為氬氣，期間的生長溫度及時間分別為800 °C及50分鐘，最終得到產物稱之為疏水性之CNT/Q-50奈米複合材料，其表層奈米碳管厚度約為143 μm，奈米碳管平均管徑約為32.4 nm，裂解溫度高達525.6 °C，具有均勻分布的奈米碳管包覆，以致於有良好的疏水特性。接著將具疏水性的CNT/Q-50作為DMC製程觸媒的擔體，在經過70小時的反應程序，其轉化率及選擇性仍然保持在最佳反應趨勢且尚未衰退，這表示支撐式奈米碳管觸媒擔體可有效的抑制觸媒老化。由於CNT/Q-50的高比表面積及導電性，能輔助Pt/TiO2光觸媒產氫，其最佳產氫量為5.0266 μmol/g-hr。此外，將具疏水性CNT/Q-50進行吸附實驗，以簡易固定床的方式將15 ppm亞甲藍溶液，以流速為2 mL/hr流經吸附材後，其吸附率高達85.4 %，表示支撐式奈米碳管也具有顯著的吸附能力及選擇性。

關鍵字

二氧化矽；奈米碳管；化學氣相沉積法；蜂巢狀催化劑

並列摘要

The objective of this study is to prepare hydrophobic carbon nanotube (CNT) layers nanocomposite on commercially spherical SiO2 catalysts supports by using thermal chemical vapor deposition (thermal CVD). Then applied this novel materials to be the monolithic catalysts for preparing oxidative carbonylation catalysts for the production of dimethyl carbonate (DMC) from methanol and improving the stability of catalysts, adjoin photocatalyst and be irradiated the sample to product hydrogen , and the last one to be adsorbent to separate the solvent. For preparing the catalyst of growth CNTs, we deposited nickel nitrate solution as a nickel catalyst precursor on the spherical SiO2 by incipient wetness impregnation, nickel catalysts content of Q-50 supports was 2.5 wt%, and the vacuum dried catalysts precursors were calcined under atmosphere at 450 °C for 30 minutes in the box furnace. The calcination of catalyst precursors was pushed into horizontal tubular furnace for growing hydrophobic CNTs layers by the thermal CVD process, where ammonia as reduction agent, acetylene as carbon source, and argon as ambient gas for heating and cooling stages. The reaction temperature and time were 800 °C and 50 minutes, respectively. Finally the products were denoted as hydrophobic CNT/Q-50 nanocomposite, which thickness of surface CNTs layers was 143 μm, the average diameter of CNTs was 32.4 nm, the thermal degradation temperature of CNT/Q-50 was up to 525.6 °C, and it have was better hydrophobic properties due to the homogeneous CNTs layers on the surface. The hydrophobic CNT/Q-50 was used as catalysts supports for DMC process. After 70 hours, the conversion and selectivity of DMC maintained the reaction tendency without degrading. It represents that supported carbon nanotube catalysts supports can inhibit catalysts aging effectively. Due to high specific surface area and conductivity of CNT/Q-50, it can help Pt/TiO2 photocatalyst to produce hydrogen. The best hydrogen gas evolution rate is 5.0266 μmol/g-hr. In addition, the hydrophobic CNT/Q-50 was employed to adsorb 15 ppm methylene blue solution by using simple fixed-bed reactor at 2 mL/hr, the adsorption rate was up to 85.4%. The above results demonstrated that supported carbon nanotube catalysts supports had prominent absorbability and selectivity.

並列關鍵字

monoliths ； SiO2 ； CNT ； CVD

參考文獻

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支撐式奈米碳管觸媒的製備與應用

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