Studies On Oxidative Dehydrogenation Of Propane Over Cesium Salts Of 12-tunstophosphoric Acid And Hydroxylation Of Benzene To Phenol Over Cu-zeolite Catalysts With Molecular Oxygen In Gas-phase

This dissertation first studied the oxidative dehydrogenation of propane over Cs salts of Keggin-type Cs_xH_3-xPW₁₂O₄₀ which were synthesized by precipitation between dilute aqueous solutions of H₃PW₁₂O₄₀ and Cs₂CO₃.From XRD,IR, N₂-adsorption,SEM,H₂-TPR and NH₃-TPD characterizations,it is clear that along the increase in Cs content of Cs_xH_3-xPW₁₂O₄₀ samples,the concentration of acid site decreased gradually,and the microstructure transformed step by step from compact large particles(for Cs_xH_3-xPW₁₂O₄₀,x＜2.0) to nano-sized spheres with which mesoporous structure was constructed(for Cs_xH_3-xPW₁₂O₄₀,x＞2.2).The relationship between catalytic behaviors and the physicochemical properties of Cs_xH_3-xPW₁₂O₄₀ samples suggests that the acidity and the microstructure played important roles on determining their catalytic performance in ODH of C₃H₈.Over the Cs_xH_3-xPW₁₂O₄₀ (0.9＜x＜2.0) catalysts without mesoporous structure,the conversion of C₃H₈ decreased along the abatement in the concentration of acid site,and the selectivity of C₃H₆ formation was much higher than those over Cs_xH_3-xPW₁₂O₄₀(2.2≤x≤2.7) catalysts.Over the Cs_xH_3-xPW₁₂O₄₀(2.2≤x≤2.7) catalysts with mesoporous structure, the conversion of C₃H₈ was slightly improved although the concentration of acid site decreased,however most of the target products C₃H₆ was converted to CO₂,probably owing to the strong adsorption effect of mesopores for C₃H₆.The highest yield of C₃H₆ was achieved over the Cs_1.5H_1.5PW₁₂O₄₀ catalyst which possessed concentrated acid site and non-porous structure.This dissertation also studied the hydroxylation of benzene with molecular oxygen in gas-phase over Cu-H-ZSM-5 catalysts which were synthesized by solid state ion exchange method.From XRD,UV-vis and H₂-TPR characterizations,it is clear that ion exchange calcination temperature,Cu loading and Si/Al ratio can change the interaction strength between Cu species and support(ZSM-5),and also the dispersion of Cu species.The state of Cu species determine the catalytic performance in hydroxylation of benzene.The maximum yield of benzene(＞10%) was achieved over the SR1123K-1.5wt%Cu-ZSM-5(25) catalyst.