Interaction of Zn²⁺ with extraframework aluminum in HBEA zeolite and its role in enhancing n-pentane isomerization

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• 作者：Nur Hidayatul Nazirah Kamarudin^a ; Aishah Abdul Jalil^a ; Sugeng Triwahyono^b ; ^{sugeng@utm.my} ; ^{sugengtw@gmail.com} ; Rino R. Mukti^c ; Muhammad Arif Ab Aziz^a ; Herma Dina Setiabudi^a ; Mohd Nazlan Mohd Muhid^d ; Halimaton Hamdan^d
• 关键词：Zn-HBEA ; Extraframework aluminum ; Bridging hydroxyl groups ; Protonic acid sites ; n-Pentane isomerization
• 刊名：Applied Catalysis A ; General
• 出版年：2012
• 期刊代码：4_0926860x
• 类别：ch
• 出版时间：26 July, 2012
• 卷：431-432
• 期：Complete
• 页码：104-112
• 文件大小：1175 K

摘要

The electrodeposition method was used to produce Zn²⁺ cation precursors, followed by the introduction of Zn²⁺ cation precursors to HBEA by the ion exchange technique. The introduction of Zn²⁺ cations slightly changed the specific surface area and crystallinity of HBEA. IR, XPS and solid state MAS NMR results showed that Zn²⁺ cations interacted with (AlO)⁺ extraframework aluminum to form Zn(OAl)₂ and simultaneously induced the formation of bridging hydroxyl groups, Si(OH)Al. The pyridine adsorbed IR study revealed that the presence of Zn²⁺ cations fully eliminated weak and partially eliminated strong Br酶nsted acid sites. As a result, strong and relatively weak Lewis acid sites were formed in which the pyridine probe molecule desorbed at 623 K and below. The presence of Zn²⁺ cations enhanced the catalytic activity of HBEA in n-pentane isomerization due to the presence of strong Lewis acid sites; the sites may facilitate the formation and maintenance of active protonic acid sites through a hydrogen spillover mechanism. At 598 K, the yield of isopentane for Zn-HBEA was 25.7%higher than that of HBEA. Within a reaction temperature range of 373-648 K, the apparent activation energy for isomerization of n-pentane over HBEA and Zn-HBEA was 118.76 and 90.79 kJ/mol, respectively.