| 摘要: | 利用電漿進行觸媒表面改質對於觸媒改良為一具有前景之技術，許多研究發現經過電漿處理過之觸媒可增加活性及穩定性。本研究將介電質放電技術 (dielectric barrier discharge, DBD)應用於Ni/Al2O3 觸媒之製作前處理，再進行乙醇蒸氣重組反應，以了解電漿氣體種類以及電漿處理在觸媒製作程序之不同對於蒸氣重組反應之影響。本研究之介電材料為石英，內徑10.6 mm，內電極直徑0.1 mm，放電長度100 mm。介電質放電實驗之固定參數包括施加電壓16 kV及頻率100 Hz，每公克觸媒施予之能量為10800焦耳，空間流速1498 hr-1，溫度為室溫，操作參數則為改變進流氣體之種類（氫氣、氧氣）以及處理順序（觸媒鍛燒前，鍛燒後）。乙醇蒸氣重組實驗之固定參數包括空間流速10602 hr-1，乙醇和水的進流莫耳比為1:3，操作參數則為反應溫度 (446、535、637、736 ℃)。 在電漿處理之觸媒與傳統觸媒之關係上，在鍛燒前以氫氣、氧氣電漿進行處理之觸媒，其乙醇轉化率，氫氣選擇性階低於傳統觸媒，在溫度為446 ℃的狀況下，傳統觸媒，氧氣電漿觸媒、氫氣電漿觸媒之乙醇轉化率分別為82.6%、61.9%、57.1%，氫氣選擇性分別為42.9%、22.8%、0.0%。隨著溫度上升至736 ℃，各觸媒的乙醇轉化率可上升至99.0%以上，傳統觸媒，氧氣電漿觸媒、氫氣電漿觸媒之氫氣選擇性分別為85.7%、71.6%、83.0%。在鍛燒後以氫氣電漿進行處理之觸媒，其乙醇轉化率，氫氣選擇性階低於傳統觸媒及氧氣電漿觸媒，在溫度為446 ℃的狀況下，傳統觸媒，氧氣電漿觸媒、氫氣電漿觸媒之乙醇轉化率分別為56.9%、39.2%、60.4%，氫氣選擇性皆為0.0%。隨著溫度上升至736 ℃，各觸媒的乙醇轉化率可上升至99.0%以上，傳統觸媒，氧氣電漿觸媒、氫氣電漿觸媒之氫氣選擇性為51.7%， 39.9%，72.5%。考慮觸媒積碳的影響，將傳統和鍛燒後經電漿處理之觸媒將溫度由高至低進行實驗，在溫度為446 ℃的狀況下，傳統觸媒，氧氣電漿觸媒、氫氣電漿觸媒之乙醇轉化率分別為79.0%、66.9%、90.6%，氫氣選擇性為42.8%、64.5%、37.4%。在736 ℃的狀況下，傳統觸媒，氧氣電漿觸媒、氫氣電漿觸媒之乙醇轉化率分別為99.8%、96.6%、99.6%，氫氣選擇性為87.0%、82.3%、92.8%。 The plasma modification of the catalyst is a novel way to improve performance of catalyst. Such prepared catalyst presents a higher catalytic activity and an enhanced stability over the catalyst prepared without plasma treatment. This study aims to evaluate the characteristics of Ni/Al2O3 catalyst for steam reforming of ethanol to syngas via a DBD by different flowing gases and with different processes. DBD reactor is made of the quartz tube with the inner diameter of 10.6 mm. A stainless steel rod with the diameter of 0.1 mm is used as the inner electrode and the length of discharge region is 100.0 mm. Experimental tests are conducted at fixed applied voltage (16 kV), frequency (100 Hz), applied energy of catalyst (10800 J/g), space velocity (1498 hr-1) and temperature (25 ℃), while the flowing gases include hydrogen and oxygen, the processes include discharge before and after calcination. Steam reforming experimental tests are conducted at fixed space velocity (10602 hr-1), ethanol-water mole ratio (1:3), while the temperature vary from 446 ℃ to 736 ℃. The catalyst prepared with discharge before calcination exhibits lower ethanol conversion rate and hydrogen selectivity, compared to the catalyst prepared without plasma treatment. At 446 ℃, ethanol conversion efficiency of traditional, O2 plasma and H2 plasma catalyst are 82.6%, 61.9% and 57.1%, H2 selectivities of each one are 42.9%, 22.8% and 0.0%, respectively. At 736 ℃, ethanol conversion efficiency of each catalyst reaches to above 99.0%, H2 selectivities of traditional, O2 plasma and H2 plasma catalyst are 85.7%, 71.6% and 83.0%, respectively. At another case, the catalyst prepared with discharge after calcination by H2 plasma shows improved ethanol conversion rate and hydrogen selectivity, compared to O2 plasma and tranditional catalyst. At 446 ℃, ethanol conversion efficiency of O2 plasma and H2 plasma catalyst are 56.9%, 39.2% and 60.4%, the H2 selectivities of each one are all 0.0%. At 736 ℃, the ethanol conversion efficiency of each catalyst reach above 99.0%, H2 selectivities of traditional, O2 plasma and H2 plasma catalyst are 51.7%, 39.9% and 72.5%, respectively. In order to reduce the effect of coke formation, the catalyst discharged after calcination conducts steam reforming process by temperature decrease way, at 446 ℃, ethanol conversion efficiency of traditional, O2 plasma and H2 plasma catalyst are 79.0%, 66.9% and 90.6%, H2 selectivities of each one are 42.8%, 64.5%, 37.4%, respectively. At 736 ℃, ethanol conversion efficiency of each catalyst are able to reach to above 99.0%, H2 selectivities of each one are 42.8%, 64.5%, 37.4%, respectively. 87.0%, 82.3%, 92.8%. The present investigation confirms the DBD treatment of Ni/γ-Al2O3 catalyst with hydrogen after calcination thermally, leads to better activity and selectivity for steam reforming of ethanol to syngas. |
