磷钨杂多酸铵盐固体酸催化剂的制备、表征及性能

以室温沉淀法制备了一系列铵取代磷钨杂多酸盐催化剂(NH4)xH3-xPW12O40(x=0.5,1.0,1.5,2.0,2.5,3.0),用X-射线衍射(XRD)、傅里叶-红外光谱(FT-IR)、固体紫外-可见漫反射光谱(DR UVVis)、扫描电镜(SEM)、氮气吸附-脱附(N2adsorption-desorption)等手段对其进行了表征,并考察了它们在H2O2氧化苯甲醛制苯甲酸反应中的催化活性.结果表明,NH4+取代H+后形成的杂多酸盐仍很好地保持了Keggin结构;随着NH4+取代度的增大,(NH4)xH3-xPW12O40的颗粒逐渐均匀,晶格常数逐渐减小,而比表面积和总孔容呈先增大后减小的趋势;在相同实验条件下,所制(NH4)xH3-xPW12O40的催化活性均优于H3PW12O4(71%),其中在(NH4)2.5H0.5PW12O40催化作用下,苯甲酸收率达到最高(76%).

Preparation,Characterization and Catalytic Behavior of Ammonium Salts of 12-tungstophosphoric Acid Solid Catalysts

A series of ammonium salts of 12-tungstophosphoric acid(( NH4)xH3- xPW12O40,x = 0. 5,1. 0,1. 5,2. 0,2. 5,3. 0) were synthesized by the precipitation method at room temperature. The resulting materials were characterized by XRD,FT-IR,DR UV-Vis,SEM,and N2adsorption-desorption. Their catalytic activities in the green synthesis of benzoic acid were evaluated under organic solvent-free conditions. The results suggested that the substitution of H+by NH4+did not change the Keggin structure of H3PW12O40. On the other hand,the particles became more uniform and the lattice constant decreased with the increase of x in( NH4)xH3- xPW12O40. Meanwhile,the specific surface area and pore volume increased to some extent and( NH4)2. 5H0. 5PW12O40 exhibited the maximum values. It was interesting that( NH4)xH3- xPW12O40 showed higher catalytic activities than that of bulk H3PW12O40( 71%),and the yield of benzoic acid may reach up to 76% over( NH4)2. 5H0. 5PW12O40.