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首页> 外文期刊>Catalysis science & technology >The relevance of Lewis acid sites on the gas phase reaction of levulinic acid into ethyl valerate using CoSBA-xAl bifunctional catalysts
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The relevance of Lewis acid sites on the gas phase reaction of levulinic acid into ethyl valerate using CoSBA-xAl bifunctional catalysts

机译：路易斯酸的相关性网站气相戊酸乙酯反应乙酰丙酸使用CoSBA-xAl双功能催化剂

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摘要

A series of Co supported on Al-modified SBA-15 catalysts has been studied in the gas phase direct transformation of levulinic acid (LA) into ethyl valerate (EV) using a continuous fixed-bed reactor and ethanol as solvent. It was observed that once the intermediate product gamma-valerolactone (GVL) has been formed, the presence of aluminum is required for the selective transformation to EV. Three Lewis acid sites (LAS) are identified (from highest to lowest acid strength): aluminum ions in tetrahedral and octahedral coordination and Co2+ sites. The intrinsic activity of these LAS for the key reaction, the GVL ring opening, decreases with the strength of these acid sites, but so does the undesirable formation of coke, also catalyzed by these centers. The best catalyst was that with the highest Al content, CoSBA-2.5Al, that reached an EV yield of up to 70%. This result is associated with the presence of LAS attributed to the presence of Co2+ surface species that, although having low intrinsic activity in the selective GVL ring-opening reaction, are highly concentrated in this sample and also possess less activity in the undesirable and deactivating formation of coke. These Co2+ LAS have been stabilized by incorporation of aluminum into the support, modifying the reducibility and dispersion of cobalt species. Additionally, the lower proportion of metallic Co species decreases the hydrogenating capacity of this catalyst. This decrease is a positive result because it prevents GVL hydrogenation to undesired products. This catalyst also showed promising stability in a 140 h on-stream run.
机译：一系列的公司支持Al-modified SBA-15在气相催化剂进行了研究直接转化乙酰丙酸(LA)戊酸乙酯(EV)使用一个连续固定床反应堆和乙醇作为溶剂。一旦中间产品gamma-valerolactone (GVL)已经形成铝需要的存在选择性转换EV。网站(LAS)标识(从最高最低的酸强度):铝离子四面体和八面体协调和Co2 +网站。GVL开环的关键反应,减少这些酸网站的实力,但可口可乐的不良的形成,也催化的中心。铝含量最高,cosba - 2.5,了电动车收益率高达70%。结果是与拉斯维加斯的存在有关归因于二氧化碳+表面的存在物种,尽管拥有较低的内在选择性活动GVL开环反应,在此示例中高度集中同时也拥有更少的活动不受欢迎的和去活化焦炭的形成。拉斯维加斯已经稳定的公司铝的支持,修改钴物种的还原能力和分散。此外,低比例的金属有限公司物种减少的加氢,能力这种催化剂。因为它可以防止GVL加氢不受欢迎的产品。承诺在140 h在工作过程中运行稳定。

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