Fe-AlPO4-5分子筛的共振拉曼光谱

利用周期性密度泛函的方法, 将过渡金属杂原子取代的硅基分子筛的共振拉曼计算结果成功推广到磷铝分子筛体系中. 根据对Fe-ZSM-5共振拉曼光谱特点的推广和对Fe-AlPO4-5振动光谱的理论计算结果, 预测在Fe-AlPO4-5的共振拉曼光谱的1190、1130、1000-1050和600 cm-1位置附近将出现四条显著的谱带. 实验的Fe-AlPO4-5的共振拉曼光谱中确实观察到四条与骨架Fe物种相关的谱带分别位于1210、1130、1050和630 cm-1处, 与预测结果一致. 另外发现含铁磷铝分子筛的共振振动频率要高于相应的含铁硅基分子筛体系的振动频率, 这种频率的差异主要是氧在不同分子筛体系中受力的力常数不同引起的. 另外磷氧四面体和铝氧四面体之间的电荷吸引作用对振动频率也有较大的影响.

Resonance Raman Spectrumof Fe-AlPO4-5 Zeolite

Resonance Raman spectrum results from the study of silica zeolites that contain transition metals by density functional theory (DFT) calculations were extended successfully to an aluminum phosphate zeolite system. Based on the study of the resonance Raman spectrum of Fe-ZSM-5 and DFT calculations of Fe-AlPO4-5, we predicted the presence of four vibrational bands at 1190, 1130, 1000-1050 and 600 cm-1 in the resonance Raman spectrum of Fe-AlPO4-5. Experimentally those four bands were found at 1210, 1130, 1050, and 630 cm-1 in the Raman spectrum of Fe-AlPO4-5, excited by a 244 nmlaser, and were assigned to the framework Fe species. The resonance Raman spectrum of Fe-AlPO4-5 is similar to that of the Fe-ZSM-5 zeolite since both zeolites have similar tetrahedrally coordinated Fe species in the framework. However, the vibrational frequencies of Fe-AlPO4-5 are higher than those of Fe-ZSM-5 because of the higher force constant of oxygen in Al—O—P than in Si—O—Si. Furthermore, the effect of the electrostatic attraction between the PO4 tetrahedron and the AlO4 tetrahedron is found to be important to the vibrational frequencies.