鈣-鎳-鋁水滑石觸媒對於乙醇蒸氣重組反應之二氧化碳捕獲及產氫研究

Abstract

本研究以鈣-鎳-鋁層狀水滑石結構做為前驅物，製備出一系列不同鈣-鎳莫耳比例之鈣-鎳-鋁氧化物。首先利用X光繞射(XRD)鑑定結構，並以電子顯微鏡(SEM)、比表面積儀(BET)分析其物理特性。藉由熱重分析(TGA)對其二氧化碳捕獲能力與穩定性進行量測，結果發現鈣-鎳-鋁氧化物之最佳捕獲溫度範圍約在600-700℃之間，經15次捕獲/脫附循環迴圈測試後，其材料仍可保有極高的二氧化碳捕獲量約41.6wt%，且無明顯劣化的跡象，其捕獲循環維持率約為98%，展現出極佳的穩定性。 其次，針對鈣-鎳-鋁氧化物應用於乙醇重組系統催化之效能探討，實驗以兩組乙醇重組系統進行分析：第一部分為通入氮氣的二氧化碳捕獲強化重組產氫系統，在此系統中，水-乙醇進料比例、反應溫度等操作條件改變皆會對二氧化碳捕獲與乙醇重組產生顯著影響。經由二氧化碳捕獲強化輔助，鎳含量0.15之樣品於水-乙醇莫耳比為5、催化溫度為600℃的條件下可獲得最高產氫量約5.14莫耳。第二部分則為通入空氣的乙醇自供熱重組系統。相較於調變催化溫度，實驗發現將鈣-鎳-鋁氧化物還原成金屬觸媒的方式更可有效獲得高氫氣產出。其中，高鎳含量0.67之樣品經還原後可具有最高之氫氣產量約3.15莫耳；即使減少鎳含量如0.33之樣品，其經長時間乙醇重組連續測試24小時，氫氣產量亦可達2.98莫耳，維持在96%，擁有優秀的催化穩定性；而低鎳含量0.15的樣品經還原後，則可獲得最多的氫氣提升量0.76莫耳。 綜合以上結果，鈣-鎳-鋁氧化物兼具優異的穩定性、良好的二氧化碳捕獲及氫氣產量，本研究成功開發出具備二氧化碳捕獲與乙醇重組催化效能之多功能鈣-鎳-鋁複合材料。

This study presentsthe experimental results of ethanol steam reforming to produce hydrogenviaCa-Ni-Al mixed oxidesderived from hydrotalcite-like compounds (HTlcs). These multifunctional catalysts were characterized by X-ray powder diffraction(XRD), scanning electron microscopy (SEM) and Nitrogenadsorption/desorptionisotherms. In addition, theperformance of CO2capture was evaluatedby thermogravimetry analysis(TGA). Owing to homogeneous distributedCa, Ni and Aloxides, the catalystshoweda high capacity of CO2and high stability of cyclic reactions during the carbonation/ decarbonation cycles in the range of 600-700℃. To further investigatethe catalytic activities in the process of ethanol steam reforming, two different systems, sorption enhanced steam reforming(SESRE) and autothermal reforming of ethanol(ATRE), were chosen to examine the performance. Inthe first part, it was found that optimizingthe molar ratio of steam/ethanol and the operating temperature would benefitboththe capacity of captured CO2and the production of hydrogen. The maximum yield of hydrogenas 5.14mol/mol ethanol was obtained from overLDO-Ni-0.15 catalystwith S/E=5 at 600℃. Furthermore, in the second part, it was demonstrated that not only the production of hydrogen but the catalyticstability could be more obviously improved by reducing the NiO to Ni,which was more prominent forthe Ni-poor catalysts. Finally, multifunctionalCa-Ni-Al oxide catalyst was successfully developed withhigh hydrogenproduction enhanced by excellentCO2capture capacity.