摘要
研究了微量氧对Mo/HZSM 5沸石上甲烷芳构化反应的影响 .结果表明 ,氧的浓度存在阈值 ,当甲烷中氧的浓度低于阈值时 ,氧的加入可提高Mo/HZSM 5沸石对甲烷芳构化反应的稳定性 ;高于此值则发生甲烷的完全氧化反应 .用紫外拉曼光谱和紫外激光诱导荧光光谱对在不同氧浓度的甲烷中反应后的Mo/HZSM 5样品进行了表征 .催化剂上的积碳量 ,钼物种的碳化程度以及反应后样品在 5 2 0～ 5 80nm间出现的荧光谱带峰位都随反应气氛中氧浓度的增加而降低 .完全氧化时 ,钼物种被氧化为氧化钼 ,而此时荧光谱带下降到 5 2 0nm .可以认为 ,荧光光谱的变化反映了钼物种的碳化程度 ,从而可将发生完全氧化反应后Mo/HZSM 5样品的 5 2 0nm荧光谱带归属为氧化钼 ,而 5 80nm附近的谱带可归属为MoOxCy;加氧时 ,MoOxCy/HZSM
The effect of oxygen on aromatization of methane over Mo/HZSM-5 zeolite was studied. It was found that there exists a threshold value of the oxygen concentration. The durability of Mo/HZSM-5 zeolite in aromatization of methane is greatly improved by the added oxygen when the oxygen concentration is lower than the threshold value; otherwise, the total oxidation of methane takes place. The Mo/HZSM-5 samples after aromatization of methane in the presence of oxygen was characterized by UV-Raman spectroscopy and laser induced fluorescence spectroscopy (LIFS). It was disclosed that the amount of coke, the carburization degree of molybdenum species and the wavelength of a band at 520 similar to 580 nm in the LIFS of Mo/HZSM-5 zeolite decrease monotenously with the rising of oxygen concentration. It was suggested that the variation of the LIFS band with the oxygen concentration originates from the difference in the caburization degree of molybdenum species. The band at similar to580 nm in LIFS is tentatively assigned to MoOxCy/HZSM-5 and the band at 520 nm to MoO3/HZSM-5. So MoOxCy/HZSM-5 can be suggested to be the active phase for aromatization of methane over Mo/HZSM-5 in the presence of oxygen.
出处
《催化学报》
SCIE
CAS
CSCD
北大核心
2002年第2期150-152,共3页
基金
国家重点基础研究规划项目 (G19990 2 2 40 7)
