H₅CoW₁₂O₄₀ supported on nano silica from rice husk ash: A green bifunctional catalyst for the reaction of alcohols with cyclic and acyclic 1,3-dicarbonyl compounds

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• 作者：Ezzat Rafiee^a ; ^{e.rafiei@razi.ac.ir} ; ^{ezzat_rafiee@yahoo.com} ; Maryam Khodayari^a ; Masoud Kahrizi^a ; Reza Tayebee^b
• 关键词：Nano catalyst ; 12-Tungestocobaltic acid ; Bifunctional catalyst ; Supported catalyst ; 尾-Keto enol ethers
• 刊名：Journal of Molecular Catalysis A ; Chemical
• 出版年：2012
• 期刊代码：57_13811169
• 类别：ch
• 出版时间：June, 2012
• 卷：358
• 期：Complete
• 页码：121-128
• 文件大小：1467 K

摘要

Rice husk ash (RHA) is an abundant agricultural by-product. The present research work deals with the production of nano silica powders, with high surface area and in amorphous form, from RHA using optimized technique. 12-Tungestocobaltic acid, H₅CoW₁₂O₄₀ (CoW), was supported on silica from RHA to produce silica supported CoW (CoW/NSiO₂) as a nano catalyst. The characterization data derived from FT-IR reveal that the Keggin structure of CoW remains intact in CoW/NSiO₂. TEM image showed that the catalyst had spherical shape with an average particle size of 10 nm. The acidity of the catalyst was measured by potentiometric titration with n-butylamine. To our surprise, this very strong solid acid catalyst showed an excellent distribution of acid sites, suggesting that the catalyst possesses a higher number of surface active sites compared to CoW supported on commercial silica (CoW/SiO₂), CoW and K₅CoW₁₂O₄₀. A high catalytic activity was found over CoW/NSiO₂. Finally, CoW/NSiO₂ has been used as a highly effective catalyst for benzylation of linear 1,3-dicarbonyl compounds with benzylic alcohols and synthesis of 尾-keto enol ethers from cyclic 1,3-dicarbonyl compounds. The present methodology offers a practical, simple, mild, environmentally friendly, and timesaving method under solvent-free conditions.