TiO2-Catalyzed n-Valeraldehyde Self-Condensation to 2-Propyl-2-Heptenal: Acid Catalysis or Base Catalysis?

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• 作者：Lili Zhao ; Hualiang An ; Xinqiang Zhao ; Yanji Wang
• 刊名：Industrial & Engineering Chemistry Research
• 出版年：2016
• 出版时间：December 7, 2016
• 年：2016
• 卷：55
• 期：48
• 页码：12326-12333
• 全文大小：336K
• ISSN：1520-5045

文摘

Several TiO₂ samples with different morphologies and structures, nano/microcomposite of TiO₂ (anatase), TiO₂ whisker (anatase), and nano-TiO₂ (anatase), were prepared and characterized by means of N₂ adsorption–desorption, CO₂-TPD, and NH₃-TPD, and their catalytic performance for n-valeraldehyde self-condensation was investigated. The results indicated that the conversion of n-valeraldehyde was correlated with their acid amount while the selectivity of 2-propyl-2-heptenal was associated with their base amount. Since the catalytic performance of nano-TiO₂ (anatase) was the best, its preparation process was further studied and the suitable preparation conditions were obtained. Then the effect of reaction conditions on the catalytic performance of nano-TiO₂ (anatase) for n-valeraldehyde self-condensation was investigated and the suitable reaction conditions were obtained as follows: a weight percentage of TiO₂ catalyst of 15 wt %, a reaction temperature of 190 °C, and a reaction time of 10 h. Under the above reaction conditions, the conversion of n-valeraldehyde, 2-propyl-2-heptenal yield, and selectivity were 94.6%, 93.7%, and 99.1%, respectively. The TiO₂ catalyst could be reused four times without a significant loss in its catalytic performance, which was different from most of the literature. The catalytic stability of TiO₂ catalyst was associated with the properties of the active sites, especially acid–base property. Not as some of the literature claimed that their TiO₂-catalyzed reactions were base-catalyzed reactions, the TiO₂ catalyst used in this work possessed much greater acid amount than base amount. To assess the role of acidic and basic sites in n-valeraldehyde self-condensation, ammonia and carbon dioxide were separately used as a probe molecule for poisoning the corresponding active sites. The results confirmed the key role of acid sites in n-valeraldehyde self-condensation. Therefore, we were convinced that the TiO₂-catalyzed n-valeraldehyde self-condensation was mainly an acid-catalyzed reaction.