The basic units of the framework structure of HZSM-5 zeolite are the five-membered rings which are linked by bridging oxygen atoms and as a result form units of four-membered rings or six membered rings. Semiempirical...The basic units of the framework structure of HZSM-5 zeolite are the five-membered rings which are linked by bridging oxygen atoms and as a result form units of four-membered rings or six membered rings. Semiempirical CNDO/2 quantum chemical method is used to calculate the charge density distribution for all these basic units, i.e., 4-, 5- and 6-membered rings of HZSM-5 zeolite. Quantitative relations between the structural parameter α<sub>0</sub> of the acidity of HZSM-5 zeolite and the number of aluminum atoms N<sub>Al</sub> per unit cell are obtained. Zeolite may be considered as solids acting more or less as protonic polyacids in solution. This protonic acidity is expressed as activity, a<sub>H<sup>+</sup></sub>= [H<sup>+</sup>]f<sub>H<sup>+</sup></sub> ,were =n<sub>H<sup>+</sup></sub>aN<sub>Al</sub>/Z<sub>cat</sub> and the activity coefficient f<sub>H<sup>+</sup></sub> is equal to a constant multiplied by the structural parameter, f<sub>H<sup>+</sup></sub>= Kα<sub>0</sub>, K is taken to be 32. Upder different （SiO<sub>2</sub>/Al<sub>2</sub>O<sub>3</sub>） ratios, therefore, the protonic activities could be obtained theoretically, and the calculation results are展开更多
文摘The basic units of the framework structure of HZSM-5 zeolite are the five-membered rings which are linked by bridging oxygen atoms and as a result form units of four-membered rings or six membered rings. Semiempirical CNDO/2 quantum chemical method is used to calculate the charge density distribution for all these basic units, i.e., 4-, 5- and 6-membered rings of HZSM-5 zeolite. Quantitative relations between the structural parameter α<sub>0</sub> of the acidity of HZSM-5 zeolite and the number of aluminum atoms N<sub>Al</sub> per unit cell are obtained. Zeolite may be considered as solids acting more or less as protonic polyacids in solution. This protonic acidity is expressed as activity, a<sub>H<sup>+</sup></sub>= [H<sup>+</sup>]f<sub>H<sup>+</sup></sub> ,were =n<sub>H<sup>+</sup></sub>aN<sub>Al</sub>/Z<sub>cat</sub> and the activity coefficient f<sub>H<sup>+</sup></sub> is equal to a constant multiplied by the structural parameter, f<sub>H<sup>+</sup></sub>= Kα<sub>0</sub>, K is taken to be 32. Upder different （SiO<sub>2</sub>/Al<sub>2</sub>O<sub>3</sub>） ratios, therefore, the protonic activities could be obtained theoretically, and the calculation results are
