奈米金觸媒在富氫氣流中選擇性一氧化碳氧化之應用;Selective Oxidation of CO in Hydrogen Stream over gold catalysts

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Title:	奈米金觸媒在富氫氣流中選擇性一氧化碳氧化之應用;Selective Oxidation of CO in Hydrogen Stream over gold catalysts
Authors:	鄭雯璟;Cheng,Wen-ching
Contributors:	化學工程與材料工程研究所
Keywords:	金觸媒;銀;一氧化碳氧化;二氧化鈰;燃料電池;CeO2;CO oxidation;silver;gold;PROX;fuel cell
Date:	2012-06-19
Issue Date:	2012-09-11 18:10:52 (UTC+8)
Publisher:	國立中央大學
Abstract:	燃料電池除了能高效率的把化學能轉化成電能，更是一種方便攜帶的能源。在燃料電池產氫能的過程中會產出副產物一氧化碳，一氧化碳會毒化白金電極，而選擇性氧化一氧化碳反應(PROX)將一氧化碳減至< 5 ppm，是目前最能有效移除一氧化碳方法之一。本研究將金及銀或銠之奈米顆粒擔載於二氧化鈰上，並應用於富氫氣流中之一氧化碳選擇性氧化反應中。金-銀/二氧化鈰是以沉積沉澱法製備；另一方面，銠則是以含浸法方式與二氧化鈰擔體混合，之後再使用沉積沉澱法將金顆粒擔載於上述擔體。在此研究中，改變不同的促進劑比例和擔體鍛燒溫度找出最佳的條件以製備出最適合PROX反應之金觸媒。製備完成的觸媒經過X光繞射分析儀、穿透式電子顯微鏡、X光電子能譜儀和感應耦合電漿質譜分析儀等鑑定分析其觸媒性質。PROX反應是在固定床反應器中填充0.1克觸媒，並以進料氣體CO/O2/H2/He 體積比為1.33/1.33/65.33/32.01，總流量控制在50 ml/min下進行反應。結果顯示金-銀/二氧化鈰觸媒及金-銠/二氧化鈰觸媒在80-100℃對一氧化碳的轉化率及轉化率皆比金/二氧化鈰觸媒更好。其中金-銀(1:1)/二氧化鈰觸媒在80℃下更可將一氧化碳完全轉化。金以2-5奈米的大小分佈於擔體上。加入銀後，銀失去的電子可使吸附的氧分子解離成氧原子，有助於二氧化碳的形成，此外，電子也可使金的正三價離子轉變成金屬態，也有助於一氧化碳選擇性氧化反應。另一方面，反應中一氧化碳之選擇性隨銀的添加量而提高。金-銠/二氧化鈰觸媒在較高的觸媒鍛燒溫度下(350℃)在轉化率及選擇率上才有比較明顯的促進作用。兩種觸媒在燃料電池操作溫度(65-100℃)下進行反應，金-銀(1:1)/二氧化鈰觸媒鍛燒溫度180℃的觸媒可在80℃將一氧化碳完全轉化。Nanoscaled gold, silver and gold, rhodium particles supported on CeO2 was used for preferential oxidation of carbon monoxide in hydrogen-rich stream (PROX). They were loaded on CeO2 through deposition-precipitation method. The catalysts with different amounts of silver and different calcination temperatures were tested to develop the best catalyst for PROX reaction. These catalysts were characterized by XRD, TEM, XPS, and TPR. The PROX reaction was carried out in a fixed bed continuous flow reactor with a feed of CO: O2: H2: He = 1.33: 1.33: 65.33: 32.01 in volume ratios. The results showed that the catalyst with specific Ag content and calcinations temperature could reach 100% of CO conversion at the PEM fuel cells operating temperature (65℃-100℃) even as the gold content was 0.5 wt. %. The particle size of gold was around 2-5 nm and Au particles were dispersed well on the support. In Au-Ag/CeO2 catalysts, the higher calcination temperature resulted sintering of gold, leading to the lower activity. The CO selectivity increased with increasing silver amount. The promotional effect of rhodium addition was more obvious at higher calcination temperature (350℃) of catalyst. However, the exist of this hydroxide did not show significant promotion on catalytic selectivity. These two kinds of catalyst underwent reaction with operating temperature 80℃, the Au-Ag/CeO2 (1:1) catalysts calcined at 180℃ can converted CO to CO2 completely.
Appears in Collections:	[化學工程與材料工程研究所] 博碩士論文

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