Thermally Stable Amorphous Mesoporous Aluminophosphates with Controllable P/Al Ratio: Synthesis, Characterization, and Catalytic Performance for Selective O-Methylation of Catechol

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• 作者：Gang Liu ; Zhenlü ; Wang ; Mingjun Jia ; Xiujing Zou ; Xiaomei Zhu ; Wenxiang Zhang ; Dazhen Jiang
• 刊名：Journal of Physical Chemistry B
• 出版年：2006
• 出版时间：August 31, 2006
• 年：2006
• 卷：110
• 期：34
• 页码：16953 - 16960
• 全文大小：258K
• 年卷期：v.110,no.34(August 31, 2006)
• ISSN：1520-5207

文摘

Amorphous mesoporous aluminophosphates (AlPO) with P/Al molar ratio in the range 0.8-1.15 are synthesizedby using the citric acid (CA) route and are systematically characterized using N₂-adsorption, XRD, SEM,solid-state CP-MAS NMR, FT-IR, TG-DTA, CO₂-TPD, and NH₃-TPD. The characterization studies showthat the change in P/Al ratio could affect the structure, texture, thermal stability, and surface acid-baseproperties of AlPO. Samples with a relatively low P/Al ratio (1.0) exhibit uniform amorphous mesoporouscharacter and high thermal stability (up to 1173 K). Partial crystallization of the AlPO framework easilyoccurred on the sample with higher P/Al ratio (1.1), thus leading to significant decrease of surface area andformation of particle pile mesopores. Both weak acid and weak base sites are observed over AlPO materials,and the amounts of acid-base sites can be effectively controlled by adjusting the P/Al ratio. The presence ofsuitable interaction between citric acid and AlPO framework is critical for the formation of mesoporousstructures. Both CA and PO₄ units are considered to be ligands to coordinate with aluminum ions, formingrelative uniform complexes (such as CA-Al-PO₄) in the as-synthesized AlPO materials. The mesoporousstructure of AlPO materials is obtained after the rapid decomposition of citric acid. Vapor phase selectiveO-methylation of catechol with methanol reaction is carried out to investigate the catalytic performances ofAlPO materials with different P/Al ratios. Among them, AlP_1.1O shows the highest activity (88.4% conversionof catechol) and the highest yield of guaiacol (74.3%). The presence of suitable weak acid-base pairs mayplay an important role on the title reaction.