CATALYTIC OXIDATION OF TOLUENE AND METHYL ETHYL KETONE OVER LA-SR-MN PEROVSKITE CATALYSTS

摘要

This study investigates the catalytic oxidation of toluene and methyl ethyl ketone (MEK) over La_(1-x)Sr_xMnO_3 (x = 0, 0.3, 0.5, 0.7, 1.0) catalysts. The experimental results indicate that catalyst has the highest activity. Toluene and MEK are 95% destroyed over catalyst at 300 and 196℃, respectively. The catalytic activity is enhanced when the catalyst is pretreated with an N_2 stream for 1 hour at 400℃, that catalyst is in the reduced-state. The temperature for the 95% destruction of toluene over reduced-state La_(0.7)Sr_(0.3)MnO_3 catalyst is 267℃. The decreased temperature is possibly attributed to that some lattice oxygen of the catalyst is lost in the preheating process without oxygen. The catalytic reaction shifts from superficial to interfacial, thereby enhancing the catalytic activity. Acetaldehyde and butyrolactone are observed in the oxidation of MEK as the intermediate products. The maximum yield of intermediate products occurs at the temperature where about 50% of MEK is destroyed over each catalyst. In addition, the mechanisms of the MEK oxidation are discussed. The temperature of 95% destruction of toluene increases with the increasing concentration of MEK in the reaction. The experimental results also demonstrate that toluene catalytically incinerates after the conversion rate of MEK reaches more than 90%. This may be caused by MEK being adsorbed easily at the active site and thus being oxidized more than toluene. The weight-hour space velocity limit for the oxidation of 4,000 ppm toluene is 24,000 mL hr~(-1) g~(-1). Therefore, the oxidation of toluene is inhibited before the complete oxidation of MEK. Finally, the adsorption equilibrium constant, the apparent reaction rate constant, and the activation energy of these reactions are evaluated using experimental results.