钾对镁铝水滑石复合氧化物的表面改性

Surface Modification of Mg-Al Hydrotalcite Mixed Oxides with Potassium

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≤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.

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 that K was 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.