| Summary: | 碩士 === 國立臺灣科技大學 === 化學工程系 === 95 === This study used a nanosized FeZSM-5 and a series of modified FeZSM-5 to to produce phenol by direct oxidation of benzene. Nitrous oxide was the oxidant. FeZSM-5 was modified in four ways: incorporation of copper by impregnation, treating with steam, treating with steam and acid, and adding carbon nanotubes in the synthesis.
The catalysts synthesized for this study were characterized by XRD for the crystalline structures, by FESEM for the morphology, by nitrogen adsorption for the BET surface and micropore volume, by ICP-AES for the composition, and by NH3-TPR for knowing the acid strength distribution..
The activities of the catalysts were measured at 1 atm and 300-550oC, using a continuous flow micro-reactor loaded with 0.3 g catalyst. The total feed rate to the reactor was maintained at 396 mmol/min. The result showed that the optimum reaction temperature was 450oC. Carrying out the reaction at a temperature lower than 450oC would only give insufficient phenol yield. A temperature higher than 450oC would cause excessive catalyst deactivation, hence lower the yield of phenol. The selectivity to phenol increased with an increase in the ratio of benzene/N2O. A maximum selectivity of 93% was obtained at a ratio of 3.56. An activation period of 80 min was found for a newly synthesized FeZSM-5. The catalyst was stable after the activation for a 4 hours test run.
An incorporation of small amount of copper ( < 0.2 wt %) could enhance the activity of the FeZSM-5. But excess copper ( > 1 wt %) resulted in a lower activity due possibly to the clog of the pores by the copper. Steam treatment as well as steam plus acid treatments could both partially remove the aluminum and iron in FeZSM-5. The removal resulted in a decrease in the number of acid sites and an increase in the strength of the sites. As a consequence, the activity of the treated FeZSM-5, at least in 300-500oC, was reduced. The selectivity of CO, however, was not altered. The steam and acid treated FeZSM-5, due possibly to its higher thermal stability, exhibited a higher activity than the untreated counter part at a reaction temperature between 500-550oC. Adding carbon nanotubes in synthesizing could change the size of the FeZSM-5 crystals. Some of the crystals were found to be penetrated by the tubes. But the content of FeZSM-5 in the synthesized product was lower than that prepared without the tubes. As a consequence, the activity of the catalyst synthesized with the tubes was also lower. However, if purity factor was removed and the comparison was made on the same amount of pure FeZSM-5 basis, the FeZSM-5 prepared with the tubes showed higher activity than that synthesized without the tubes.
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