| Summary: | 碩士 === 義守大學 === 生物技術與化學工程研究所碩士班 === 98 === Reverse micelles-synthesized copper nanoparticles supported on cerium oxide for selective CO oxidation in rich hydrogen is studied in this work. To prepare the catalyst, the copper nanoparticles were destabilized from the microemulsion, and thus quickly adsorbed onto the cerium oxide powder. XRD patterns exhibited the characteristic peaks of cerium oxide only. No diffraction lines corresponding to those of copper species were detected, indicating very good dispersion of the nano-sized copper on the carrier. Activity test of the 0.5 wt% CuO/CeO2 catalyst (0.01 M copper ion concentration) showed that 30% conversion of CO was attained at 80℃. The CO selectivity remained almost at 100% for temperatures below 110℃, indicating that hydrogen at these temperatures would not affect the CO oxidation reaction. However, when the temperature exceeded 110℃, hydrogen was energetically enough to be dissociatively adsorbed on the catalyst surface to compete with CO for interfacial oxygen ions, thus inhibiting the activity of CO oxidation. CO was not easily converted into CO2 under the influence of hydrogen. When temperature exceeded 130℃, the hydrogen was ‘lighted off’, though the light-off was not very significant so that the selectivity declined slowly. This temperature depends on the interaction of CO and H2 for interfacial oxygen ions. It was observed, from the study of the competitive oxidation of CO and H2 at temperatures higher than that of hydrogen ‘light-off’, that CO exhibited a higher oxidation activity in the competitive oxidation of CO and H2, thereby limiting the accessibility of hydrogen to oxygen.
The effects of different concentrations of copper ions and copper loadings were investigated also. It was found that much better oxidation activity could be obtained from the catalyst of 2 wt% CuO/CeO2 prepared by 0.01 M copper ion concentration. The conversion of CO was 46% at 80℃, while at 120℃ the CO conversion was able to reach 100% and the selectivity still maintained at about 80%. The performance of the copper catalyst synthesized in this work is comparable to that of the precious metal catalyst, yet with economic advantages.
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