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以磷钨酸和过渡金属盐在pH值为4.0~5.0的条件下合成了4种具有Keggin结构的单过渡金属配位磷钨酸铵盐NH4MPW11(M=Zr2+,Co2+,Ni2+,Cu2+),通过红外、紫外、热重、X射线衍射、循环伏安法等技术对这类杂多化合物的结构和性质进行了表征,并考察了它们在环己酮氨肟化反应中的催化性能.结果表明:单过渡金属配位的磷钨酸铵盐NH4MPW11(M=Zr2+,Co2+,Ni2+,Cu2+)具有典型的Keggin结构,过渡金属离子配位后,热稳定性和氧化性增强;在催化环己酮氨肟化反应中,NH4MPW11的催化性能低于单缺位磷钨酸铵盐(NH4PW11),其中NH4ZrPW1 1为催化剂,性能优于M=Co2+,Ni2+,Cu2+的催化剂,环己酮的转化率达到85.1%,环己酮肟的选择性达到92.1%,而NH4CuPW11的催化性能则下降显著;H2O2的分解实验表明,过渡金属配位的磷钨酸铵盐对H2O2分解均存在一定的促进作用,分解能力随过渡金属种类而变化,其中NH4CuPW1 1对H2O2的分解率高达72.3%,这是造成过渡金属配位的磷钨酸铵盐在环己酮氨肟化反应中催化性能下降的主要原因;回收催化剂的红外和XRD表征表明,氨肟化反应后的NH4MPW11保持了Keggin型的一级结构,但二级结构遭到一定程度的破坏.
Four kinds of single transition metal complex phosphotungstate NH4MPW11 (M = Zr2 +, Co2 +, Ni2 +, Cu2 +) with Keggin structure were synthesized by using phosphotungstic acid and transition metal salt at pH 4.0 ~ 5.0. The structures and properties of these heteropoly compounds were characterized by IR, UV, TG, X-ray diffraction and cyclic voltammetry, and their catalytic performances in the ammoximation of cyclohexanone were also investigated. : A single transition metal coordination ammonium phosphotungstate NH4MPW11 (M = Zr2 +, Co2 +, Ni2 +, Cu2 +) has a typical Keggin structure, transition metal ions coordination, thermal stability and oxidation enhanced; in the catalytic cyclohexanone In the course of ammoximation, the catalytic performance of NH4MPW11 is lower than NH4PW11, NH4PW1 1 is better than that of M = Co2 +, Ni2 + and Cu2 +, and the conversion of cyclohexanone reaches 85.1%, the selectivity of cyclohexanone oxime reached 92.1%, while the catalytic performance of NH4CuPW11 decreased significantly. The decomposition experiments of H2O2 showed that the transition metal coordinated ammonium phosphotungstic acid could promote the decomposition of H2O2 to a certain degree, Capacity changes with the transition metal species, of which NH4CuPW1 1 H2O2 decomposition rate as high as 7 2.3% .This is the main reason for the decrease of the catalytic performance of the ammonium phosphotungstate coordinated by the transition metal in cyclohexanone ammoximation. The IR and XRD characterization of the recovered catalyst showed that the NH4MPW11 after the ammoximation remained Keggin-type primary structure, but the secondary structure has been a certain degree of damage.