Citation: ZHANG Ye-Xin, SU Qing-Yun, WANG Zhong-Peng, GAO Xi-Yan, ZHANG Zhao-Liang. Surface Modification of Mg-Al Hydrotalcite Mixed Oxides with Potassium[J]. Acta Physico-Chimica Sinica, 2010, 26(04): 921-926. doi: 10.3866/PKU.WHXB20100446
钾对镁铝水滑石复合氧化物的表面改性
利用X射线衍射(XRD), X射线光电子能谱(XPS), 原位红外(in situ IR)光谱和CO2程序升温脱附(CO2-TPD)等技术研究了K对Mg-Al水滑石复合氧化物(MgAlO)的表面改性. 结果表明, 当K负载量臆8%(w)时, K高度分散在MgAlO表面, 并与载体作用形成了新的Lewis碱位. 其中, K取代MgAlO弱碱位OH上的质子形成弱碱性的Mg(Al)-O-K; 与强碱位表面O2-结合形成强碱性的Mg-O-K. 当K负载量为5%-8%(w)时, 还存在与载体作用较弱并具有更强碱性的准自由KOx. K增强MgAlO碱性的本质是K的电荷转移到了表面氧负离子上.
English
Surface Modification of Mg-Al Hydrotalcite Mixed Oxides with Potassium
The surface modification of Mg-Al hydrotalcite mixed oxides (MgAlO) with K was investigated using X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), in situ infrared (in situ IR) spectroscopy, and temperature-programmed desorption of CO2 (CO2-TPD).We found thatKwas highly dispersed on the surface of MgAlO when the loading amount was less than 8% (w). New Lewis base sites were formed through the interaction between K and MgAlO. The weakly basic Mg(Al)-O-K resulted from the proton substitution of Mg(Al)-OH with K. Mg-O-K was obtained by combination with strongly basic O2- sites. At a K loading between 5% (w) and 8% (w), the quasi free KOx species that interacted weakly with the support and showed stronger basicity than Mg-O-K was formed. The increase in basicity of K/MgAlO can be attributed to charge transfer from K to the surface oxygen anions, which increases the negative charge of the strongly basic sites.
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Key words:
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In situ IR
- / Hydrotalcite
- / Potassium
- / Surface modification
- / Basic site
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