不同方法脱铝八面沸石性质研究——Ⅱ.孔道结构研究

STUDY ON FAUJASITES DEALUMINATED WITH DIFFERENT METHODS——Ⅱ.STUDY ON PORE STEUCTURE

研究了SiCl_4、(NH_4)_2SiF_6、H_2C_2O_4及水热脱铝沸石的孔道结构。结果表明,所有脱铝方法均不能影响沸石晶粒大小的变化;SiCl)_4和(NH_4)_2SiF_6脱铝沸石基本上保持了沸石原有的孔道结构,而H_2C_2O_4和水热法脱铝则可导致沸石中出现40(?)左右的大量中孔结构,且H_2C_2O_4脱铝沸石的中孔孔径较为集中;在脱铝过程中,沸石的骨架崩塌以及中孔的形成都存在有某些规律性。随着沸石骨架Si/Al 比的增加,沸石由亲水性逐渐变为憎水性,而对烃的吸附能力则与体相铝含量有一致关系。

From the pore diameter distribution data of dealuminated Y-zeolites,the following facts can be observed:NH_4Y has almost no secondary pores;H_2C_2O_4 and hydrothermal dealumination causes the formation of mesopore system at a diameter of 40(?) which is not evident for(NH_4)_2SiF_6,SiCl_4 dealuminated Y-zeolites.As to high-temperature hydrothermally treated Y-zeolites,mesopores with larger diameter around 60～200(?) emerge.Pore structure among crystal particles does not change by the analysis of N_2-isotherms and TEM regardless the dealumination method. Much attention should be paid to the fact that mesopores of dealuminated Y-zeolites concentrate on 40(?),with no obvious relation to dealumination method.It is perhaps due to partial β cages collapse and finially to two to three suppercages connected.Further collapse of β cages of Y-zeolites under high temperature hydrothermal treatment contributes to larger mesopores formation around 60～200(?). No matter what dealumination method is used,the amount of H_2O adsorption on Y-zeolites de- creases with increasing framework Si/Al ratios.Comparing to chemically dealuminated Y-zeolites with the same framework Si/Al ratio,hydrothermally dealuminated Y-zeolites show low H_2O ad- sorption amounting only to a quarter of NH_4Y's for HUSY-750.The results demonstrate that high temperature hydrothermal treatment can reduce Y-zeolite's polarity greatly. As to hydrocarbons,n-hexane,decalin,Al content in Y-zeolite bulk has a decisive effect on their hydrocarbon adsorption amount.