【摘要】 研究了铌酸催化剂的制备方法、表面酸性及晶体结构对乙醇和乙酸酯化反应的影响．结果表明，热处理温度对水洗法制备的铌酸催化剂的催化性能有显著的影响，经３５０℃热处理后其达到活性极大值．并发现催化性能受热处理温度影响的原因是铌酸结构中含水量及比表面积随热处理温度变化而导致铌酸表面酸性的变化，而与氧化铌的形态和晶体结构无明显关系．更多还原

【Abstract】 Hydrated niobic pentoxide or niobic acid is a unique and promising solid acid catalyst for its mode rate acid strength and water-resistance property.This paper investigated the effect of the following factors,i.e.preparation method ,pretreatment temperature and crystalline structure,of catalyst on its activity for probe reaction.The catalyst samples were prepared by three different methods,i.e.water-washing（Ⅰ）,hydrothermal treatment in dilute H₂SO₄（Ⅱ） and K₂S₂O₇ fusion（Ⅲ）.They were characterized by N₂ adsorption at 77K,TA,XRD,TEM,IR spectra of adsorbed pyridine and esterification reaction of ethanol with acetic acid.It was found that pretreatment temperature strongly affected the acidity,acid strength and therefore activity of the catalysts.As treatment temperature increased,the specific surface area and acid amount of（Ⅰ）decreased, while the activity passed a maximum at 350℃.To account for the phenomenon of activity maximum appeared at 350℃,we correlated the acid amount with the acid strength （by IR spectrum of pyridine degassed at different temperatures）.It was found that with the treatment temperature increasing in the range of 200-450℃,the amount of Lewis acid decreased while the amount of Bronstad acid with a certain strength （corresponding to pyridine degassed at 200℃） remained constant. The amount of both strong Lewis and Bronsted acid（corresponding to pyridine degassed at 350℃）,however,exhibited maximum for treatment temperature of 350℃.It was the compensation effect of acid strength for the amount that caused the maximum of activity for treatment temperature of 350℃.Tanabe explained that the sample treated at 500℃ lost its activity considerably was due to crystallization.Chen Z.H. found that β-phase crystalline niobic acid pre pared by hydrothermal treatment in dilute H₂SO₄ exhibited much higher activity than amorphous niobic acid prepared by water-washing. On the contrary,we found that the three samples with different structure prepared by different methods. i.e. amorphous （Ⅲ）,amorphous plus minor amount of crystal（Ⅰ）and α-phase crysal（Ⅱ） had essentially the same activity.Hence the strong influence of treatment temperature on the catalytic behavior may be attributed to the change in surface area and water content of the catalyst,not to the change in crystal structure.更多还原