SO_4^(2-)/SiO_2表面酸性的红外光谱和密度泛函理论研究  

FT-IR and Density Functional Theory Studies on Surface Acidity of SO_4^(2-)/SiO_2

作　　者：郭岱石[1] 马紫峰[1] 蒋淇忠[1] 叶伟东[2] 李春波[2] 

机构地区：[1]上海交通大学化学工程系,上海200240 [2]浙江医药股份有限公司新昌制药厂,浙江新昌312500

出　　处：《催化学报》2007年第7期627-634,共8页

基　　金：国家自然科学基金(20476055);教育部高等学校博士学科点专项科研基金(20060248064);新世纪优秀人才支持计划(2004)

摘　　要：对介孔SiO2及硫酸根促进的SiO2样品进行了原位吡啶吸附红外光谱测试,分别建立了硫酸根促进前后的SiO2表面原子簇模型,用密度泛函理论对其吡啶吸附行为进行了计算,分析了SO42-/SiO2表面酸性产生的机理.实验和计算结果表明,SO42-/SiO2表面不存在Lewis酸中心,原位红外谱图中表征Lewis酸性的特征峰对应于氢键吸附吡啶的环振动,这种氢键作用因SiO2表面的硫酸根促进而得到加强.HSO4-螯合结构为SO42-/SiO2表面Brφnsted酸中心,其酸强度强于表面磺酸基团修饰的介孔SiO2材料SO3H-MSU,而弱于HZSM-5.SO42-/SiO2的酸催化活性源于其表面的Brφnsted酸性.Silica MCM-41 without and with sulfuration treatment was measured by in situ pyridine adsorption infrared spectroscopy. Cluster models of pure SiO2 and SO4^2- /SiO2 were built up, and density functional theory calculations on pyridine adsorption were carried out to analyze the surface acidity of SO4^2- /SiO2. The combined results of experimental and theoretical studies showed that there were no Lewis acid sites on the surface of SO4^2-/SiO2. The IR frequencies assignable to Lewis acidity corresponded to the enhanced hydrogen-bonded adsorption of pyridine by sulfuration treatment. The chelating structure of HSO4^- acts as Bronsted sites on the surface of SO4^2-/SiO2, with an acid strength higher than that of sulfonic group-functionalized silica SO3H-MSU but weaker than that of HZSM-5. The acid catalytic activity of SO4^2-/SiO2 results from the BrФnsted acidity.

关 键 词：二氧化硅 硫酸根 表面酸性 吡啶吸附 红外光谱 密度泛函理论 

分 类 号：O643.3[理学—物理化学]