Au/TiO2觸媒催化NO+CO反應特性研究

李美銀(Mei-Yin Lee)

指導教授 ： 林昇佃

元智大學/工程學院/化學工程與材料科學學系/碩士(1997年)

摘要

本研究主要在討論不同製備方法製得Au/TiO2觸媒催化NO+CO反應特性研究。以含浸法製得觸媒經120℃烘箱乾燥(DO)後以HTR/C/LTR-II還原所得活性較佳，粗略估計其催化NO→N2O之活化能(Ea)為-5.0Kcal/mole，而催化NO→N2之活化能Ea則約為1.7Kcal/mole；含浸法觸媒經室溫抽真空乾燥(DR)後則是以CO/H2O(g)還原較HTR/C/LTR還原條件來得好，且從323K-623K都是以N2為主產物。即使進料只通入NO，發現仍有明顯NO分解反應活性。而以HAuCl4為precursor製得Au/TiO2所得反應活性均沒有以AuCl3為precursor來得好。
以沈澱法製備過程而言，TiO2擔體懸浮液pH值愈高所得反應活性愈好而以NaOH調整pH值的活性也優於NH4OH，實驗發現以pH=11.4(NaOH)經CO/H2O(g)還原所得反應活性為最佳，其催化NO→N2O之活化能(Ea)為-3.1Kcal/mole ，NO→N2之活化能Ea約為2.4 Kcal/ mole，且測得對NO的反應級數約為1級。
表面紅外光譜分析(DRIFTS)方面，在323K時，通入CO ，在2186cm-1可見一吸收峰為CO在TiO2的訊號，而在2120cm-1有一CO在Au上的訊號。而通入NO時，則以NO吸附在TiO2的訊號為主。而含浸法Au/TiO2 (HTR/C/LTR-II)在323K下通入CO時，比Au/TiO2(HTR/C/LTR-I)在1820cm-1多了一吸收峰，只通入NO時也多了2167cm-1此訊號，這些額外訊號的形成有可能是造成這兩種含浸法Au/TiO2經HTR/C/LTR觸媒在323-523K範圍內不同NO+CO反應選擇性的主要原因。

關鍵字

Au/TiO2觸媒 ； NO+CO反應 ； 含浸法 ； 沈澱法 ； HTR/C/LTR還原 ； CO/H2O(g)還原 ； 表面紅外光譜分析

並列摘要

The NO+CO reaction was studies over Au/TiO2 catalysts prepared by either the impregnation or the deposition method. The drying conditions and pretreatment conditions were found to affect the reactivity. The prepration parameters such as pH value the type of alkaline also effected the reactivity of those prepared by the deposition method.
For catalysts prepared by the impregnation method, the incipiently wet powders were dried either in a 393K oven (DO) or under vacuum at 298K (DR) .For the DO sample, a pretreatment sequence of high temperature reduction/calcination low temperature reduction (HTR/C/LTR) showed the best activity. The NO to N2 activation energy was —5.0 Kcal/mole and the NO to N2O activation energy was 1.7Kcal/mole. For the DR sample, a reduction by CO/H2O(g) at 343K had the highest NO reduction activty. The most active Au/TiO2(DR,CO/H2O(g)) produced mainly N2 whereas the others involved the production of N2O. At 323K, this sample yields N2 at a selectivity of 100%. HAuCl4/TiO2 prepared by the impregnation method was found to have lower activities than corresponding AuCl3/TiO2 catalysts.
For the deposition method, the activity increased with the increasing pH of TiO2 solution. A catalyst prepared at pH=11.4 (adjusted by NaOH) had the highest NO reduction activity after a reduction by CO/H2O (g) at 343K.
Analyses with Diffuse Reflectance Infrared-Fourier Transform Spectroscopy (DRIFTS) showed various CO and NO absorbance features over these Au catalysts. A slight change in the HTR/C/LTR pretreatment caused somewhat different reaction selectivity and different IR absorbance band.

並列關鍵字

HASH(0xd9c82e0)

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