Acidity study of X zeolites modified by nickel and/or chromium cations in the case of binary and ternary exchanges

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• 作者：Souhila Bendenia^a ; Isabelle Batonneau-Gener^b ; Jean-dominique Comparot^b ; Kheira Marouf-Khelifa^a ; Habib Hammoudi^a ; Amine Khelifa^a ; ^{aminekhelifadz@yahoo.fr}
• 关键词：NaX zeolite ; Ternary exchange ; Textural properties ; Pyridine ; Acidity
• 刊名：Microporous and Mesoporous Materials
• 出版年：2012
• 期刊代码：78_13871811
• 类别：ch
• 出版时间：1 September, 2012
• 卷：159
• 期：Complete
• 页码：111-118
• 文件大小：609 K

摘要

A series of Ni(x)-, Cr(x) and CrNi(x)-exchanged X zeolites (x being the ion-exchange degree) was prepared and characterised by nitrogen adsorption, XRD, DTA/TGA and pyridine adsorption-desorption followed by IR spectroscopy. The objective is mainly to estimate quantitatively the number, strength and nature of acid sites and their dependence on the type of cation and its exchange level. A comparison between the binary and ternary exchanges was also established. The crystallinity and micropore volume losses were more significant for Cr(x)X and CrNi(x)X. The concentration of Lewis acid sites decreases with increasing the exchange degree for Cr(x)X and Ni(x)X, while it increases up to 39%for CrNi(x)X. An increase of the concentration of Br酶nsted sites was obtained. The fact that both the Lewis and Br酶nsted acidities markedly decrease between 423 and 623 K, proves that the available acid sites are overall weak. The pyridine desorption from the protonic sites is easier with CrNi(39)X than with Cr(39)X and Ni(40)X at 623 K, indicating a decrease in the strength in the case of ternary exchange.