亚磷酸和水蒸气联合改性的HZSM-5的物化性质和催化性能研究

考察了由亚磷酸改性的HZSM-5在673、873和1073K温度下100％水蒸气处理样品的物化和催化性质。采用XRD表征了样品的结构。通过吸附吡啶红外光谱和NH3-TPD进行了酸性和酸分布研究。XPS的研究结果表明，P由 3价氧化成了 5价，并提出了可能的改性的表面结构模型。通过N2吸附．脱附等温线研究了样品的孔结构，样品的吸附-脱附等温线为Ⅰ型和Ⅳ型的复合型，滞后环为IUPAC分类的H4型。Al的状态由^27Al MAS NMS表征。采用AMl(Austin Model I)半经验量子化学方法和模型簇法筛选了磷改性可能的两种结构模型，其区别在于磷上的桥氧与铝配位还是端氧与铝配位，结果表明端氧与铝配位的可能性更大。以正庚烷裂化反应为探针反应考察了样品的活性。

EFFECT OF STEAM TREATMENT AND PHOSPHOROUS ACID MODIFICATION OF HZSM-5 ON ITS PHYSICOCHEMICAL AND CATALYTIC PROPERTIES

Physicochemical and catalytic properties of phosphorous acid modified HZSM 5 zeolites treated with 100% steam at 673，873，and 1073*!K have been investigated.The structure of the samples was characterized by XRD.The acidity and distribution of the acidic sites were studied by IR using pyridine as probe molecule and temperature programmed desorption (TPD) of ammonia.The state of phosphorus were studied by XPS，showing that P (Ⅲ) was oxidized to P(Ⅴ)，a model for the surface structure of the modification is proposed.The textural properties of catalysts determined by nitrogen isothermal adsorption desorption measurements suggest the isothermal type of all samples is a combination of type Ⅰ and type Ⅳ，all hysteresis loops resemble the H4 type in the IUPAC classification.The state of aluminum was characterized by 27Al MAS NMR spectroscopy.AM1 (Austin model) semi empirical method and cluster model method have been employed to study the stability of two possible phosphorus modified zeolite geometries，the difference was the bridging oxygen of phosphorus coordination with aluminum or the terminal oxygen of phosphorus coordination with aluminum.The result showed that the terminal oxygen coordination was more possible according to the heat of formation (HF).The n heptane cracking reaction was selected as probe reaction to investigate the activity of studied samples.