镧离子在Y型分子筛中的定位及迁移规律

Location and Migration Rule of Lanthanum Ions in Y Zeolite

综合运用X射线光电子能谱(XPS)、X射线荧光光谱(XRF)、X射线衍射谱(XRD)及吡啶吸附红外光谱(Py-IR)等多种表征技术研究了镧离子在镧含量不同的Y型分子筛中的定位情况,并用高分辨XRD Rietveld结构精修验证了综合表征的结论。结果表明:当La_(2)O_(3)质量分数为4%、8%、10%、12%和14%时,镧离子基本能迁移进Y型分子筛β笼;当La_(2)O_(3)质量分数为16%时,有相当一部分镧离子留在Y型分子筛超笼。进一步应用原位水热XRD研究了镧改性Y型分子筛在水热处理过程中(二交二焙工艺)的结构变化,原位观察到了镧离子在此过程中的迁移规律:即在一次离子交换后镧离子大部分定位于超笼,经一次焙烧后大部分镧离子迁移到β笼,二次焙烧后镧离子几乎全部迁移到β笼。

The location of lanthanum(La)ions in Y zeolites with different La contents was studied by a number of characterization techniques,including X-ray photoelectron spectroscopy(XPS),X-ray fluorescence(XRF),X-ray diffraction(XRD)and Py-Fourier transform infrared spectroscopy(Py-IR),and the comprehensive characterization result was verified by high-resolution XRD Rietveld structure refinement.The results show that La ions can basically migrate intoβcage of Y zeolites when the mass fractions of La_(2)O_(3)are 4%,8%,10%,12%and 14%;when the mass fraction of La_(2)O_(3)is 16%,a considerable amount of La ions remain in the supercage of Y zeolites.In situ hydrothermal XRD was further applied to investigate the structural changes of lanthanum-modified Y zeolites in the hydrothermal process(double-exchange double-calcination method),and the migration rule of La ions in this process was observed in situ,that is La ions mostly located in the supercage after primary ion exchange,La ions mostly migrated intoβcage after primary calcination,and almost all La ions migrated intoβcage after secondary calcination.