Properties and Characterization of Modified HZSM-5 Zeolites

摘要/Abstract

摘要： Physicochemical and catalytic properties of phosphorus and boron modified HZSM-5 zeolites treated with 100% steam at 673 K were investigated. The acidity and distribution of acidic sites were stud- ied by infrared spectroscopy using pyridine as probe molecule and temperature programmed desorption (TPD) of ammonia. The structure of the samples was characterized by XRD, and the textural properties of the catalysts were determined by nitrogen isothermal adsorption-desorption measurements and scanning electron microscopy (SEM). The XRD results show that the modified samples have no novel crystalline phase, indicating a high dispersion of phosphorus and boron species. After treatment, the microporous volume and surface area of the samples markedly decrease, implying the blockage of the channel. The nitro- gen adsorption-desorption measurements suggest that the isothermal type of all samples is a combination of isothermal type I and IV, and all hysteresis loops resemble the H4-type in the IUPAC classification. The total acidity of the modified samples, determined by pyridine adsorption IR and TPD of ammonia, decreases in contrast to that of the parent HZSM-5. The conversion of n-heptane over P and B steam- modified HZSM-5 is higher than that of P and B-modified HZSM-5 zeolites but lower than that of the parent HZSM-5.

关键词: HZSM-5 zeolite, steam treatment, phosphorus, boron, secondary pore, texture, cracking activity

Abstract: Physicochemical and catalytic properties of phosphorus and boron modified HZSM-5 zeolites treated with 100% steam at 673 K were investigated. The acidity and distribution of acidic sites were stud- ied by infrared spectroscopy using pyridine as probe molecule and temperature programmed desorption (TPD) of ammonia. The structure of the samples was characterized by XRD, and the textural properties of the catalysts were determined by nitrogen isothermal adsorption-desorption measurements and scanning electron microscopy (SEM). The XRD results show that the modified samples have no novel crystalline phase, indicating a high dispersion of phosphorus and boron species. After treatment, the microporous volume and surface area of the samples markedly decrease, implying the blockage of the channel. The nitro- gen adsorption-desorption measurements suggest that the isothermal type of all samples is a combination of isothermal type I and IV, and all hysteresis loops resemble the H4-type in the IUPAC classification. The total acidity of the modified samples, determined by pyridine adsorption IR and TPD of ammonia, decreases in contrast to that of the parent HZSM-5. The conversion of n-heptane over P and B steam- modified HZSM-5 is higher than that of P and B-modified HZSM-5 zeolites but lower than that of the parent HZSM-5.

Key words: HZSM-5 zeolite, steam treatment, phosphorus, boron, secondary pore, texture, cracking activity

Renqing Lü;Hejin Tangbo;Qiuying Wang;Shouhe Xiang. Properties and Characterization of Modified HZSM-5 Zeolites[J]. 能源化学(英文), 2003, 12 (1): 56-62.

Renqing Lü;Hejin Tangbo;Qiuying Wang;Shouhe Xiang. Properties and Characterization of Modified HZSM-5 Zeolites[J]. Journal of Energy Chemistry, 2003, 12 (1): 56-62.

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