本研究以沈澱法製備1% Au/γ-Al2O3觸媒,並進行CO的氧化反應,探討沈澱時的pH值、前處理條件及製備過程中原物料添加順序對觸媒活性的影響。發現適當的鹼添加和前處理,所製得的1% Au/γ-Al2O3觸媒,對CO氧化反應的催化活性與1.5% Au/TiO2參考觸媒相當。 比較不同前處理之鍛燒溫度與鍛燒時間,發現以20% O2 於573K下鍛燒2小時最能提高金觸媒活性。前處理鍛燒溫度不足時,轉化率較低,但經過573K反應測試後轉化率會有上升的現象,顯示觸媒可能因前處理溫度不足而未被完全活化。原物料添加順序中,發現以先將氧化物擔體添加鹼改變懸浮溶液pH值,再將金溶液滴入為最佳。 CO氧化反應動力學分析方面,經由Arrhenius plot顯示1% Au/γ-Al2O3觸媒的活化能約6.1 kcal/mole,在238K~228K之間似乎有轉折現象而非線性,若此轉折現象是存在,則不同溫度範圍活化能分別為11.3 kcal/mole (>243K)及6.3 kcal/mole (<223K)。CO氧化反應於243K、253K與263K下,CO與O2反應級數分別為-1與0.2,1.5% Au/TiO2參考觸媒在此溫度範圍下的反應級數也相同,顯示此級數範圍符合金觸媒Single site L-H反應動力學速率式,但無法確定O2為分解吸附或非分解吸附。 由1% Au/γ-Al2O3觸媒與1.5% Au/TiO2參考觸媒對於CO與O2的吸附行為分析中顯示,自製Au/γ-Al2O3觸媒與Au/TiO2參考觸媒皆有真空下氣體釋放現象,但Au/γ-Al2O3放出量明顯較低,這個真空環境下的氣體釋放現象會干擾吸附行為分析,致使可信度下降。
Alumina-supported gold catalysts were prepared by deposition-precipitation method. The preparation parameters investigated include pH, pretreatment , sequence of raw material addition. The Au/γ-Al2O3 prepared at pH >9.5 became very active for CO oxidation above at 213K after a calcination at 573K for 2h. This activity is similar to the 1.5% Au/TiO2 reference catalyst. With a feed of 1% CO+10% O2 in He, almost 90% of the CO was converted at 298K at CO a space velocity of 21,415 μ mole/g-cat/h. Lower CO oxidation activity was observed, when the calcination temperature reduced to 473K or when a calcination time of 1h was used. Kinetic studies were performed with both 1% Au/γ-Al2O3 and 1.5% Au/TiO2. Both catalysts showed a near -1 order rate dependence on CO and a near 0.2 order rate dependence on O2 between 213K and 253K. This conforms to a single-site Langmuir-Hinshelwood rate model. However, it is not sure whether the O2 was dissociative or nondissociative adsorbed.