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利用量子力学中的密度泛函理论(DFT),对EU-1分子筛中与T1、T2、T3、T6、T7、T8位相邻的骨架铝原子的落位稳定性及酸强度进行理论计算.通过计算得知,双Al原子在EU-1分子筛骨架中优先落位于Al7(Si6-Si7)Al8、Al1(Si2-Si2)Al1、Al2(Si1-Si2)Al2、Al1(Si2-Si2)Al3、Al1(Si2)Al3;根据(Al/Si,H)取代能确定了质子的落位,质子氢较易落位于(O12-H)Al1-(O12-H)Al1、(O12-H)Al1-Al1(O13-H)、(O12-H)Al1-Al1(O12-H)、(O14-H)Al2-(O14-H)Al2、Al2(O12-H)-(O14-H)Al2、Al1(O12-H)-(O15-H)Al3、(O26-H)Al7-Al8(O28-H);且根据质子亲和势分析知,EU-1分子筛骨架中质子氢落位于NNN位的Brnsted酸强度小于NNNN位.借助1H MAS NMR分析合成的不同硅铝比的样品,可知硅铝比低的EU-1分子筛Brnsted酸吸收峰的面积增加;由NH3-TPD可知硅铝比低的EU-1分子筛的强酸脱附峰温度降低,酸强度减小.硅铝比低的EU-1分子筛的强酸表现出酸量高、酸强度低的性质.
Based on the density functional theory (DFT) in quantum mechanics, the dislocation stability and acid strength of framework aluminum atoms adjacent to T1, T2, T3, T6, T7 and T8 in EU-1 molecular sieve were theoretically calculated. It is found from calculation that the double Al atoms preferentially fall on Al7 (Si6-Si7) Al8, Al1 (Si2-Si2) Al1, Al2 (Si1- Si2) Al2, Al1 (Si2- Si2) Al3, (O12-H) Al1- (O12-H) Al1, (O12-H) Al1-Al1 (Si2) Al3 can be easily determined by the substitution of (Al / Si, H) (O12-H) Al1-Al1 (O12-H), (O14-H) Al2- (O14-H) Al2, Al2 (O12-H) - (O14-H) Al2, Al1 (O12-H) - (O15-H) Al3, (O26-H) Al7-Al8 (O28-H). According to the proton affinity analysis, the proton in the EU-1 zeolite framework is located at the NNN nsted acid strength is less than NNNN.HPAS NMR analysis of the synthesized samples with different Si / Al ratios shows that the area of Brnsted acid absorption peak of EU-1 molecular sieve with low Si / Al ratio increases. The Si / Al ratio Low EU-1 molecular sieve strong acid desorption peak temperature decreases, the acid strength decreases. EU-1 zeolites with low silica to alumina ratio show strong acids with high acid strength and low acid strength.