Al2O3掺杂SO4^2-/SnO2固体酸催化剂上的酯化和酯交换反应

Esterification and Transesterification on Al_2O_3-Doped Sulfated Tin Oxide Solid Acid Catalysts

用共沉淀法制备了一系列不同Al2O3掺杂量(0.5%-3.0%,摩尔分数)的SO24-/SnO2催化剂.采用N2吸附、热重(TG)分析、X射线粉末衍射(XRD)、X射线光电子能谱(XPS)、漫反射红外光谱(DRIFTS)、拉曼(Raman)光谱、魔角旋转固体核磁共振(27AlMASNMR)对催化剂的结构和织构性质进行了表征,用正丁胺电位滴定法测定了催化剂的酸量,并评价了这些催化剂对月桂酸与甲醇的酯化和三乙酸甘油酯与甲醇的酯交换反应性能.实验结果表明SO24-/SnO2催化剂中掺杂少量Al2O3能明显提高催化活性,这是由催化剂的酸性位增加而引起的,添加Al2O3的摩尔分数为1.0%的催化剂表现出最高的反应活性,在酯化反应中6h后月桂酸转化率高达92.7%,在酯交换反应中8h后三乙酸甘油酯转化率高达91.1%.

A series of Al2O3-doped （0.5%-3.0%, molar fraction） sulfated tin oxide catalysts were prepared by a co-precipitation method.The structures and textural properties of these catalysts were characterized by N2 adsorption, thermogravimetric （TG） analysis, X-ray diffraction （XRD）, X-ray photoelectron spectroscopy （XPS）, diffuse reflectance infrared Fourier transform spectroscopy （DRIFTS）, Raman spectroscopy, and 27Al magic-angle spinning nuclear magnetic resonance （MAS NMR）.The number of acid sites on the catalysts was measured by the potentiometric titration of n-butylamine.Their catalytic performance for the esterification of lauric acid with methanol and the transesterification of triacetin with methanol was also investigated.The results showed that the addition of Al2O3 to sulfated tin oxide improved the catalytic activity markedly.The remarkable activities of the Al2O3-doped catalysts are caused by the larger number of acid sites.The SO4^2-/SnO2 catalyst doped with a 1.0% molar fraction of Al2O3 exhibited the highest activity.The lauric acid conversion was 92.7% after esterification for 6 h, and the triacetin conversion was 91.1% after transesterification for 8 h on this catalyst.