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利用脉冲微反和程序升温脱附研究磷、镁和磷-镁改质沸石的酸性、正己烷的裂化和氢转移活性以及烯烃选择性。当 HZSM-5上磷和镁含量增加时,反应条件下吡啶中毒所得到的酸中心数、裂化活性和单位酸中心上转化频率降低。在3%磷改性的 HZSM-5上加入镁时,沸石的酸中心数、裂化活性和单位酸中心上转化频率都随着镁含量增加而增加。结果还表明,裂化反应主要是在强酸中心上进行,随着沸石的酸性降低,氢转移反应减弱,烯烃选择性增加。氨的 TPD 表明,HZSM-5沸石上强弱酸中心随着磷或镁含量增加而减小,而且强酸中心比弱酸中心下降得快,当磷或镁含量达一定值时,强酸峰消失。在含3%PHZSM-5上,强酸中心和弱酸中心随镁含量增加而增加。
The acidity of phosphorus, magnesium and phosphorus-magnesium modified zeolites, the cracking and hydrogen transfer activities of n-hexane and the selectivity of olefins were investigated by means of pulse micro-reversion and temperature programmed desorption. When the content of phosphorus and magnesium in HZSM-5 was increased, the number of acid sites, the activity of cracking and the frequency of conversion on the center of the unit of pyridine were decreased under the reaction conditions. When 3% phosphorous-modified HZSM-5 was added to magnesium, the zeolite acid number, the cracking activity and the frequency of conversion per unit of nucleus increased with the increase of magnesium content. The results also show that the cracking reaction is mainly carried out at a strong acid site, and as the acidity of the zeolite decreases, the hydrogen transfer reaction diminishes and the olefin selectivity increases. The TPD of ammonia shows that the strong and weak acid sites on HZSM-5 zeolite decrease with the increase of phosphorus or magnesium content, and the strong acid sites decrease faster than the weak acid sites. When the phosphorus or magnesium content reaches a certain value, the strong acid peaks disappear. On the 3% PHZSM-5, the strong acid center and the weak acid center increased with the increase of magnesium content.