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首页> 外文期刊>Journal of Catalysis >Effects of the thermal stability and the fine structure changes of strontium hydroxyapatites ion-exchanged with lead on methane oxidation in the presence and absence of tetrachloromethane
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Effects of the thermal stability and the fine structure changes of strontium hydroxyapatites ion-exchanged with lead on methane oxidation in the presence and absence of tetrachloromethane

机译：有无四氯甲烷与铅离子交换的羟锶磷灰石的热稳定性和精细结构变化对甲烷氧化的影响

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The oxidation of methane has been investigated in the presence and absence of tetrachloromethane (TCM) on strontium hydroxyapatite with (SrPbHAp) and without (SrHAp) ion-exchanged lead. In the absence of TCM at 873 K, the introduction of lead to strontium hydroxyapatite resulted in a substantial increase in the selectivity to C-2 hydrocarbons and an increase in the conversion of methane and specific activities. In the presence of TCM, the conversion of methane and the selectivity to C-2 compounds decreased with increasing time-on-stream while that to carbon monoxide increased. However, the change in the specific activities with time-on-stream is dependent upon the composition of the catalysts. Some SrPbHAp catalysts showed evidence of transformation from apatites to the corresponding phosphates at temperatures greater than 873 K. At 773 K, at which temperature the aforementioned hydroxyapatites are relatively stable, no formation of C-2 compounds was observed in the absence of TCM, and the conversion of methane and the specific activities (with the exception of SrPb26HAp at 0.5 h on-stream) increased with the lead content of the catalysts. On introduction of TCM, the selectivities to CH3Cl and CO2 increased and decreased, respectively, on both SrHAp and SrPbHAp catalysts. The results of extended X-ray absorption fine structure (EXAFS) spectroscopic measurements suggest that the catalytic properties of SrPbHAp at 773 K in the absence of TCM are related to the nearest-neighbor distances of the Pb-O bond rather than those of the Sr-O bond. (C) 1998 Academic Press. [References: 48]
机译：在有（SrPbHAp）和无（SrHAp）离子交换铅的条件下，在羟基磷灰石锶上存在和不存在四氯甲烷（TCM）的情况下，研究了甲烷的氧化。在没有873 K的TCM的情况下，将铅引入羟基磷灰石锶中导致对C-2烃的选择性大大提高，并且甲烷转化率和比活度增加。在TCM存在下，甲烷的转化率和对C-2化合物的选择性随运行时间的增加而降低，而对一氧化碳的转化率则增加。但是，比活性随生产时间的变化取决于催化剂的组成。一些SrPbHAp催化剂在高于873 K的温度下显示出从磷灰石转变为相应的磷酸盐的证据。在773 K时，上述羟基磷灰石相对稳定，在没有TCM的情况下未观察到C-2化合物的形成，并且甲烷的转化率和比活度（在运行0.5 h时SrPb26HAp除外）随催化剂中铅含量的增加而增加。引入TCM后，SrHAp和SrPbHAp催化剂对CH3Cl和CO2的选择性分别升高和降低。扩展X射线吸收精细结构（EXAFS）光谱测量的结果表明，在没有TCM的情况下，SrPbHAp在773 K处的催化性能与Pb-O键的最近邻居距离有关，而不与Sr的最近邻距离有关。 -O键。 （C）1998年学术出版社。 [参考：48]

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