The Preparation And Characterization And Applied Research Of Phosphotungstate Catalyst

The heteropoly compound is a kind of compound both have strong acidity and have strong oxidisability, that it not only is easy to dissolve in water and the oxo organic solvent, but also has "pseudo liquid Phase" in solid state, is one kind of ideal catalyst therefore. The applying field at present is not broad, because of whose reaction mechanism is still not vague. The heteropoly salts with different catalysis function can be get by changing the counter-balance cation of heteropoly compounds. Two kinds of heteropoly salts were prepared by double decomposition reaction in this paper, and the samples' structure have been characterized by ultraviolet (UV) Spectroscopy, powder X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) Spectroscopy, and the the samples' thermal property have been characterized by thermogravimetry-differential scanning calorimetry (TG-DSC), and the samples' redox have been characterized by cyclic voltammetric measurements (CV).The lanthanon phosphotungstate were prepared by different amounts of lanthanum chloride, cerium chloride and neodymium chloride with Phosphotungstic acid (PTA) via double decomposition reaction. XRD analysis indicated that rare-earth element is beneficial to the dispersing of WO3 and the forming and perfecting of Phosphotungstic acid crystal, and the effect are more obvious along with the increasing of the rare earth element's amounts; And IR and UV analysis indicated that the compounds kept entire Keggin structure, the introduction of rare earth element didn't destroy the Keggin structure, but the coordination of lanthanon cation have strengthened the M-Ob-M bond and M-O_c-M bond and weakened the Td symmetrical characteristic of the Keggin structure; TG-DSC analysis indicated that the introduction of rare earth element have improved the stability of water of hydration; The CV testing indicated that the lanthanon phosphotungstate had two pairs of redox peak that gain and loss one electron, and the rare earth element made the redox more reversible. It is the esterification of acetic acid and n-butanol as probe reaction to test the catalysis of lanthanon phosphotungstate. The result indicated that the rare earth is beneficial to the esterification and the amount of rare earth had severe influence to esterification, too much rare earth will cover the active point, result in low reaction rate, too little rare earth has high acid concentration can lead side reaction, generated by-product that could cover the active point and educes the reaction rate. Cerium phosphotungstate had the best catalysis in three kinds lanthanon phosphotungstates to esterification. when Ce (B) (Ce : HPA= 1:1) is catalyst, the reaction temperature is 110°C , the mole ratio of acetic to butanol is 1: 1.2, reaction time is 2 hours, the dosage of catalyst is 4%, the acetic acid conversion rate amounted to 89.0%.The quaternary ammonium phosphotungstate were prepared by different amounts of hexadecyl trimethyl ammonium chloride (HTAC), cetyl pyridine chloride (CPC) and tetramethyl ammonium chloride (TMAC) with Phosphotungstic acid (PTA) via double decomposition reaction. XRD analysis indicated that quaternary ammonium is beneficial to the forming and perfecting of Phosphotungstic acid crystal, and the diagnostic diffraction peak of phosphotungstic acid strengthened along with the increasing amounts of the quaternary ammonium salts; And IR and UV analysis indicated that the compounds kept entire Keggin structure,but the inductive effect of methyls have weakened the M-O_b-M bond and M-O_c-M bond; The CV testing indicated that the quaternary ammonium phosphotungstate had three pairs of reversible redox peak.The catalystic oxidative desulfurization test was carried out on diesel oil under Ishii-Venturello which were composed of quaternary ammonium phosphotungstate and hydrogen peroxide. The result indicated that micellar catalysis together with phase transfer catalysis might play an important role in the oxidation process of organic sulfur compounds. When the concentration of heteropoly anion and quaternary ammonium cation exceed their critical micelle concentration respectively, there would be a flat or decreasing reaction rate. When there were inappropriate value of hydrophile-lipophile balance of quaternary ammonium cations, the raction rate was also slow. There were favorable desulfuration rate when the quaternary ammonium phosphotungstate of HTAC (B) and HMPC (B) were used as catalyst, and HMPC (B) was preferable. When the mole ratio of H₂O₂ to Diesel oil is 1:50, the temperature is 60°C , catalyst dosages were 0.100 g , the concentration of hydrogen peroxide was 30%, reaction time was 2.5 hours , the desulfuration rate used HTAC (B) and HMPC (B) to be catalyst were 98.92% and 99.47% respectively.There were similar mechanism between Oxidative desulfuration and epoxidation about Ishii-Venturello system. There was pseudo-first-order reaction kinetics equation if assumed the oxidation of organic sulfur compounds is the controlling step, and the fitting curve that draw according to the desulfurization process which HTAC (B) and HMPC (B) were used displayed a good linear relationship that confirmed the pseudo-first-order reaction kinetics.