Catalytic activity of phosphorus and steam modified HZSM-5 and the theoretical selection of phosphorus grafting model |
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Authors: | Zuogang Cao Xinhai Liu |
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Institution: | 1. College of Chemistry and Chemical Engineering, China University of Petroleum (East China), Dongying 257061, Shandong, China; 2. College of Mathematics and Computational Science, China University of Petroleum (East China), Dongying 257061, Shandong, China |
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Abstract: | The modification of HZSM-5 zeolite with phosphorus and steam has been studied. Results show that 1% phospho-rus and steam modified HZSM-5 has the highest catalytic activity for n-heptane. Physicochemical and catalytic properties of 1% phosphorus and steam modified HZSM-5 zeolites have been investigated. The X-ray diffraction (XRD) results exhibit that there is considerable variation in the relative intensity of the individual diffraction peaks. The acidity of the samples decreases with an increase in the steaming temperature, which is determined by the IR of adsorbed pyridine and temperature programmed desorption (TPD) of ammonia. The oxidation state of phosphorus shown by XPS is 5, and a model for surface structure modification is proposed. The nitrogen adsorption isotherm for all samples is a combination of type Ⅰ and type Ⅳ, all hysteresis loops resemble the H4-type. The density functional and cluster model methods have been invoked to select the phosphorus grafting model, and it was found that the phosphorus grafting model were more probable in the form of the terminal oxygen coordinating with aluminum. |
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Keywords: | HZSM-5 zeolites steam treatment phosphorous acid modification cracking activity cluster model cluster model grafting phosphorus selection theoretical modified steaming activity form terminal oxygen aluminum density functional methods hysteresis loops nitrogen adsorption isotherm combination type surface structure |
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