Modification Of Catalyst Supported Phosphotungstic Acid And Characterization Of Its Acidic Catalysis Performance

Phosphotungstic acid is a kind of environmental-friendly catalyst which has strong acidic and oxidative-catalytic centers. It is an ideal catalyst because of its dissolution in water and the polar organic solvents as well as the"pseudo liquid phase"characteristics in solid state. In order to overcome the defection of the recycling of liquid phosphotungstic acid, the supported catalyst using phosphotungstic acid as active-center and pseudo-boehmite modified by lanthanum nitrate as support was prepared in this thesis. Its dissolution was evaluated by ultraviolet spectrophotometry and its acidic catalytic performance was evaluated through the synthesis of ethyl p-hydroxybenzoate by ethanol with p-hydroxybenzoate. In addition, BET,IR,NH3- TPD,XRD and SEM were employed to analyze the surface area, pore structure, acid intensity and crystal structure of the supported phosphotungstic acid catalyst.The results showed that the optimum preparation condition of the supported phosphotun- gstic acid catalyst was proposed as follows: using thirty percent of phosphotungstic acid as active-center, pseudo-boehmite modified by two percent of lanthanum nitrate after calcination at 400℃as support. The optimum synthesis condition of ethyl p-hydroxybenzoate was also given: the reaction temperature is 80℃, the reaction time is 4 hours, the molar ratio is n (ethanol):n (p-hydroxybenzoate):n (catalyst)=4:1:0.52%, the yield is up to 85.6%, even after recycled eight times the total dissolution is only about 11.9% and the yield is still 82%. The results of analysis showed that although there was strong chemisorption between phosphotungstic acid and support, the Keggin structure of phosphotungstic remain unchangeable. Phosphotungstic acids absorb uniformly on the support or into the internal hole-channel as microcrystalline cluster, the acid strength of modified catalysts increased a little, but the total acid amount decreased.The reaction condition is moderation, the operation is easy and the secondary reaction is few. And the catalysts have not only high activity and selectivity but little corrosive effect on the equipment. The supported catalyst is a kind of environmental friendly catalyst with high supported strength, good acid and oxidation catalytic activity.