奈米氧化鈰構形控制對乙醇轉氫效率研究

Abstract

本實驗利用共沉澱法合成出氧化鈰奈米纖維，以及水熱合成法合成出氧化鈰奈米粒子，奈米柱及奈米方塊，並且使用掃描及穿透式電子顯微鏡鑑定其奈米結構以及晶體成長方向，其中氧化鈰奈米纖維為多晶結構，氧化鈰奈米柱是由兩組{ 1 1 0 }及一組{ 1 0 0 }晶面組成之柱狀體，而氧化鈰奈米方塊是由三組{ 1 0 0 }晶面組成之正方形方塊。 經過使用上述合成之奈米氧化鈰晶體，在添加重量百分比5%的銠金屬，經過測試乙醇轉換裂解產氫實驗，發現與不加控制構形及所暴露晶面的氧化鈰比較，明顯有較佳的轉換效率，在相同情況下,利用傳統涵浸法所得催化劑之氫氣選擇率約116%，而利用氧化鈰奈米柱所製成催化劑可提高10%氫氣選擇率。而上述奈米構形催化劑在長時間催化反應後由於結構穩定性不佳，使得催化效率不能維持。

In this study , two methods, including (1) coprecipritation and (2) hydrothermal processes, were carried out to generate CeO2 nanocrystals with various shapes. On the basis of on the SEM study, the first method only produced polycrystalline CeO2 whereas the second method can generate rod and cube shape of CeO2. According to the TEM images , we found that the predominantly exposed planes are {001} in cerium oxide nanocubes . The predominantly exposed planes are {001} and {110} in cerium oxide nanorods . The catalytic activity for the conversion of ethanol to hydrogen have been carried out using the 5% wt Rh/CeO2 as the catalysts with as-synthesized CeO2 rods and cubes. The results from H2 selectivity, the effect of C/O ratio and stability test indicate that the cerium oxide which exposed planes under controlled more active than catalyst with irregular shape of CeO2 particles . Under the same condition , hydrogen selectivity of the cerium oxide nanorod catalyst is 10% higher than that of the catalyst prepared by impregnation method whose hydrogen selectivity is about 116% . However , the H2 selectivity for catalyst with rod and cube CeO2 gradually decrease after 24 hours, indicating the {100} and {110} surface are not stable at high temperature .