苯在酸性氧化物上的吸附研究

The study for the adsorption of benzene over the acidic oxide

翁佳宏(C.H.Woang)

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

本研究主要針對不同酸性的氧化物，以自建流動式吸附系統進行苯的吸附及脫附實驗，由吸附等溫線、吸附時的脫氫現象和程溫脫附來研究吸脫附現象與氧化物表面酸性的關聯。吸脫附實驗係在50℃和常壓下進行，吸脫附實驗後再以程溫脫附分析留於表面上的不可逆吸附物質；此外，也藉由表面積分析儀(ASAP)和熱重分析(TGA)的分析數據，來建立氧化物的物性與酸性之間的關聯。
實驗結果顯示氧化物對苯的吸附量和吸附時脫氫現象與氧化物表面酸性有關，而且酸性較強的氧化物有不可逆吸附現象：TiO2和SO42-/TiO2的不可逆吸附等溫線屬於Type I (Langmuir isotherm)的單層吸附，SO42-/SiO2的不可逆吸附等溫線則隨苯分壓提高而上升。
由程溫脫附圖得知苯在氧化物不可逆吸附的脫附物，在質譜圖中以MS=27、 39和52出現，但並無對應的MS=78訊號，顯示有非苯分子的脫附物產生。除了SiO2在苯的程溫脫附未發現有不可逆吸物脫出外，其它不同酸性的氧化物有不同脫附峰；SiO2的脫附峰形狀因加了TiO2而改變，而硫酸處理的氧化物則有不同的酸性點產生。本研究發現苯的程溫脫附圖也能如文獻中異丙醇程溫脫附實驗來提供的氧化物表面酸性的資訊，並可應用於硫酸根處理的超強酸氧化物上來判斷其酸性點性質。

關鍵字

吸附 ； 氧化物 ； 苯 ； 程溫脫附 ； 酸性

並列摘要

The benzene adsorption (desorption) over oxides support were investigated in order to find correlation with the acidity of oxide. The oxides examined included SiO2, TiO2, TiO2/SiO2, SO42-/SiO2 and SO42-/TiO2. The benzene adsorption experiments were conducted at 50℃ and atmospheric pressure; thereafter, the surface residue on the oxides were analyzed by the temperature- programmed desorption. The adsorption isotherm, the possible dehydrogenation occurred during the adsorption process and the temperature-programmed desorption were examined using a home-made flow-type adsorption system. Besides, the physical properties of the modified oxides were studied using ASAP 2000 and TGA.
The results indicated that the benzene uptake and the degree of dehydrogenation during the adsorption were related to the oxide acidity. Furthermone, irreversible adsorption of benzene takes place on the more acidic oxides. The irreversible benzene adsorption isotherms on TiO2 and SO42-/TiO2 correspond to the Type I (Langmuir)isotherm, and that of sulfated silica increases with the pressure of benzene.
The TPD results showed that the residue due to the irreversibly adsorped benzene could be detected with MS=27, 39 and 52 in mass spectrum. Silica itself had no desorption singnal detected, but all other oxides examined showed various type of TPD spectrum. The desorption spectrum depends on the type of oxides. This suggests that the benzene-TPD may be a useful tool for characterizing the surface acidity of oxides.

並列關鍵字

adsorption ； oxide ； benzene ； temperature programmed desorption ； acidity

參考文獻

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