L-Α-谷氨酸在AL_2O_3表面的吸附和热缩合反应  

Adsorption and Thermal Condensation of L-α-Glutamic Acid on Al_2O_3

作　　者：郭丽红[1] 孟明[1] 查宇清[1] 

机构地区：[1]天津大学化工学院催化科学与工程系,天津300072

出　　处：《催化学报》2006年第2期189-194,共6页

基　　金：国家博士点专项基金(20040056028);天津大学985教育振兴行动计划资助项目

摘　　要：采用热重/差热(TG/DTA),X射线衍射(XRD)和漫反射红外光谱等手段对谷氨酸在AL2O3表面的吸附和热缩合反应进行了表征,并考察了谷氨酸水溶液平衡浓度和PH值对吸附行为的影响,探讨了原位条件下表面吸附的谷氨酸的缩合反应历程.TG/DTA结果表明,谷氨酸在AL2O3上的吸附分两个阶段:当谷氨酸水溶液的平衡浓度小于0.388 MOL/L时,吸附等温线符合LANGMUIR模型,谷氨酸分子在AL2O3表面的LEWIS酸位上发生特定位置吸附,并与载体形成了二齿螯合物;当平衡浓度大于0.388 MOL/L时,呈多层吸附,主要形成Β-谷氨酸.溶液PH值越小,谷氨酸在AL2O3上的吸附量越大.原位漫反射红外光谱表明,温度约为200℃时谷氨酸分子首先在载体表面进行分子内脱水,形成焦谷氨酸,并与载体通过二齿螯合形成具有较高热稳定性的焦谷氨酸铝盐.L-a-Glutamic acid was adsorbed on the surface of alumina from aqueous solution with different concentrations and pH values. The adsorption and thermal condensation performance of L-a-glutamic acid on alumina were investigated by thermogravimetry/differential thermal analysis, X-ray diffraction, and diffuse reflectance infrared Fourier transform spectroscopy. The results indicate that the adsorption performance is prominently influenced by the equilibrium concentration and pH value of the L-α-glutamic acid solution. When the equilibrium concentration is below 0.388 mol/L, the adsorption isotherm meets the Langmuir model; when the equilibrium concentration is above 0.388 mol/L, the multi-layer adsorption phenomena can be observed, which lead to the precipitation and crystallization of β-glutamic acid on the alumina surface. The lower the pH value is, the more L-α-glutamic acid molecules adsorb on the support. The adsorbed L-α-glutamic acid molecules bidenrarely bind to the Lewis acid sites on the alumina surface through the α-carboxyl group, making the symmetric stretching band shift from 1 376 to 1 348 cm^-1. At about 200℃, the cyclic anhydride bond is formed through the intra-molecular condensation reaction, and the main product is pyroglutamic acid, which bidentately binds to the surface of alumina to form aluminium pyroglutamate species with high thermal stability. No formation of surface acyl species, previously proposed for the related systems, was detected.

关 键 词：谷氨酸 氧化铝 吸附 热缩合 焦谷氨酸 

分 类 号：O647.31[理学—物理化学] O621.2[理学—化学]