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用Hammett指示剂法测定Y型分子筛催化剂的表面酸性,可以得到表面酸量和酸强度的信息,并可反映出表面酸性随NaOH加入量的变化.但当用于测定较小孔径的HZSM-5和氢型丝光沸石(HM)的表面酸性时,所得结果达不到理论酸量,也反映不出表面酸性随NaOH加入量的变化.而用电位滴定法可以得到良好的结果.这是由于分子筛的表面酸性分析受结构因素的制约.Y型分子筛的孔径较大,孔道体系的连通性较好,正丁胺和指示剂分子容易进入Y型分子筛的内表面,因而用Hammett指示剂法能够较好地测定其表面酸性.而HZSM和HM的孔径较小,孔道结构的连通性差,正丁胺和指示剂分子不易进入其内表面,因而用Hammett指示剂法只能测定其外表面及孔口附近表面的酸性.在HZSM-5和HM中,这部分表面的酸性比内表面上的要弱些.
Using the Hammett indicator method to determine the surface acidity of the Y zeolite catalyst, the surface acidity and acid strength information can be obtained, and the surface acidity changes with NaOH addition, but when used to determine the smaller pore size HZSM-5 And the surface acidity of the hydrogen type mordenite (HM), the obtained results do not reach the theoretical acid amount and also do not reflect the change of the surface acidity with the amount of NaOH added, but good results can be obtained by potentiometric titration, because The surface acidity of molecular sieve is controlled by the structural factors.Y-type molecular sieve has larger pore size and better connectivity of the pore system, and n-butylamine and indicator molecules can easily enter the inner surface of Y-type molecular sieve, so the Hammett indicator method can Better determination of the surface acidity.The HZSM and HM smaller pore size, pore structure connectivity is poor, n-butylamine and indicator molecules are not easy to enter the inner surface, so Hammett indicator method can only determine the outer surface and pores The acidity of the surface near the mouth In HZSM-5 and HM, the acidity of this part of the surface is weaker than that on the internal surface.