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Abstract：
The potential of aerogels as catalysts for the synthesis of a relevant class of bis-heterocyclic compounds such as bis(indolyl)methanes was investigated. In particular, the studied catalyst was a nanocomposite aerogel based on nanocrystalline nickel ferrite (NiFe2O4) dispersed on amorphous porous silica aerogel obtained by two-step sol-gel synthesis followed by gel drying under supercritical conditions and calcination treatments. It was found that the NiFe2O4/SiO2 aerogel is an active catalyst for the selected reaction, enabling high conversions at room temperature, and it proved to be active for three repeated runs. The catalytic activity can be ascribed to both the textural and acidic features of the silica matrix and of the nanocrystalline ferrite. In addition, ferrite nanocrystals provide functionality for magnetic recovery of the catalyst from the crude mixture, enabling time-effective separation from the reaction environment. Evidence of the retention of species involved in the reaction into the catalyst is also pointed out, likely due to the porosity of the aerogel together with the affinity of some species towards the silica matrix. Our work contributes to the study of aerogels as catalysts for organic reactions by demonstrating their potential as well as limitations for the room-temperature synthesis of bis(indolyl)methanes.
摘要：
研究了气凝胶作为催化剂合成相关类别的双杂环化合物如双（吲哚基）甲烷的潜力。特别是,所研究的催化剂是基于纳米晶铁氧体（NiFe2O4）的纳米复合气凝胶，其分散在通过两步溶胶-凝胶合成，然后在超临界条件下进行凝胶干燥和煅烧处理获得的无定形多孔二氧化硅气凝胶上。发现NiFe2O4/SiO2气凝胶是所选反应的活性催化剂，在室温下实现高转化率，它被证明是活跃的三个重复运行。催化活性可以归因于二氧化硅基质和纳米晶铁氧体的纹理和酸性特征。此外,铁氧体纳米晶体提供从粗混合物中磁性回收催化剂的功能，使时间有效的分离反应环境。还指出了将参与反应的物种保留到催化剂中的证据，可能是由于气凝胶的孔隙率以及某些物质对二氧化硅基质的亲和力。我们的工作通过证明气凝胶在室温合成双（吲哚基）甲烷方面的潜力和局限性，为研究气凝胶作为有机反应的催化剂做出了贡献。
