USY沸石中非骨架铝形态分析及其对沸石酸性的影响

 本文采用27AlMASNMR、BET、XRD Rietveld结构精修、IR等表征技术，通过清除和交换引入非骨架铝，研究了Y沸石中非骨架铝的形态。由27Al MAS NMR，得到0ppm非骨架铝以游离在超笼中的非骨架铝为主，30～50ppm的非骨架铝可能黏附于沸石骨架。XRD Rietveld结构精修结果表明晶体学可识别的离子态非骨架铝存在于方钠石笼的SI'和SII'位置，SI'位置的非骨架铝与沸石骨架3个O3原子及与其配位的三重轴的氧形成不稳定的四配位结构，SII'位置的Al不与沸石骨架氧形成配位。超笼中未发现可识别的离子态非骨架铝。聚合态非骨架铝的存在会堵塞沸石孔道，影响微孔吸附性能，并会掩盖B酸中心。清除非骨架铝后，可以使沸石孔道畅通，并使B酸中心得到恢复。

CHEMICAL STATE OF NON-FRAMEWORK ALUMINUM IN USY ZEOLITE AND ITS INFLUENCE ON ZEOLITE ACIDITY

The type and the chemical state of non-framework aluminum and the related influence on zeolite acidity, are investigated by means of Al27-MASNMR, N2 adsorption-desorption, XRD Rietveld refinement. The Al27-MASNMR results show that non-framework aluminum corresponding to the chemical shift at 60 ppm exists in an isolate state in the supercage and that non-framework aluminum corresponding to the chemical shift at 30~50 ppm may be bound to Y zeolite framework. XRD Rietveld refinement results indicate that crystallographically identifiable non-framework Al3+ locate at site SI' and site SII' in sodalite cage, and the non-framework Al3+ at site SI' coordinates with three framework O3 atoms and oxygen atom at [111] ternary axis to form unstable four fold coordination structure, and that non-framework Al3+ at site SII' can not coordinate with framework oxygen atom. There is not any crystallographically identifiable non-framework Al3+ in supercage. Polymeric non-framework aluminum block up pore channels of Y zeolite, influence microporous adsorption ability and cover Br?nsted acid sites. Removing polymeric non-framework aluminum, pore channels of Y zeolite become free from blockage and Br?nsted acid sites are recovered.