硅区尺寸对SAPO-34分子筛稳定性和酸性的影响

摘要

构建了SAPO-34分子筛中不同尺寸的硅区Sin(n=5,8,9,11,12,13,14),并运用色散力修正的密度泛函理论(DFT-D)方法研究了SAPO-34分子筛中不同尺寸硅区形成的难易,以及所形成硅区对SAPO-34分子筛的稳定性和酸性的影响.计算结果表明:在SAPO-34分子筛中,含Si5和Si9的硅区容易形成.硅区尺寸越大,SAPO-34分子筛的结构越稳定,酸性越强.同时给出了预测含有不同硅区的分子筛中各酸性位强弱次序的规则.%SAPO-34 molecular sieve with different sizes of Si islands Sin(n=5,8,9,11,12,13,14) was constructed and investigated using dispersion-corrected density functional theory method in order to study the formation of Si islands,and the effects on the stability and acidity of SAPO-34 molecular sieve were studied.It indicates that the Si islands including Si5 and Si9 are easy to form in SAPO-34 molecular sieve.In addition,the larger the Si island is,the more stable the structure is and the more acidity the Br(φ)nsted sites are.The rule is proposed to judge the acidic strength in SAPO-34 molecular sieve with different sizes of Si islands.