Genesis of a bi-functional acid-base site on a Cr-supported layered double hydroxide catalyst surface for one-pot synthesis of furfurals from xylose with a solid acid catalyst
Genesis of a bi-functional acid-base site on a Cr-supported layered double hydroxide catalyst surface for one-pot synthesis of furfurals from xylose with a solid acid catalyst
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DOI：
10.1039/c6cy01426g
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发表时间：
2016-01-01
影响因子：
5
通讯作者：
Ebitani, Kohki
中科院分区：
文献类型：
--
作者：
Shirotori, Mahiro;Nishimura, Shun;Ebitani, Kohki
铬负载镁铝层状双氢氧化物(Cr/Mg-Al LDH)在催化剂表面的Cr3+氧化物和镁铝LDH的紧密界面上含有双功能Lewis酸-Bronsted碱活性中心。这使得高效的醛糖-酮糖异构化成为可能。在温和条件下，固体Bronsted酸Amberlyst-15与双官能酸碱Cr/Mg-Al LDH联用时，木糖经醛糖-酮糖异构化和连续脱水一锅反应的活性高于碱性裸Mg-Al LDH、取代镁铬LDH和Lewis酸性Cr3+负载的Amberlyst-15催化剂。采用多种表征技术，以MPV还原反应为模型反应，考察了镁铝LDH的活性与铬负载量之间的相关性。结果表明：(1)在1wt%以下的Mg-Al LDH表面负载了Lewis酸性氧化铬单体。(2)此后，Cr3+物种形成小的Lewis酸性Cr3+氧化物二聚体和/或三聚体，最高可达5wt%。然后，它们覆盖在镁铝LDH表面，生成高活性的双功能Lewis酸-Bronsted碱位。(3)在5wt%以上，过量的Cr3+物种形成了惰性的镁铬和/或镁铝铬类LDH复合材料。它们被沉积在一些活性部位，导致活性降低。结果表明，随着铬负载量的不同，呋喃甲醛的产率有很大差异，其中5wt%Cr/Mg-Al LDH催化剂的产率最高(59%，18h)，这是因为在5 wt%的铬负载量下，Lewis酸性Cr3+氧化物与镁铝LDH碱性中心之间的相互作用最有效。
A Cr-supported Mg-Al layered double hydroxide (Cr/Mg-Al LDH) comprised bi-functional Lewis acid-Bronsted base active sites on the catalyst surface at close boundaries between Cr3+ oxide and Mg-Al LDH. These enabled efficient aldose-ketose isomerization. The combined use of solid Bronsted acid Amberlyst-15 and bi-functional acid-base Cr/Mg-Al LDH exhibits higher activity for one-pot transformation of xylose into furfural via aldose-ketose isomerization and successive dehydration under mild conditions than those exhibited by basic bare Mg-Al LDH, substituted Mg-Cr LDH, and Lewis acidic Cr3+ supported catalysts with Amberlyst-15. The correlation between the activity and the Cr loading amount for Mg-Al LDH was evaluated using several characterization techniques and MPV reduction as a model reaction for Lewis acidity investigation. The results show the following: (1) the monomer of Lewis acidic Cr3+ oxide is supported on the Mg-Al LDH surface below 1 wt%. (2) Thereafter, Cr3+ species form small Lewis acidic Cr3+ oxide dimers and/or trimers up to 5 wt%. Then, they cover the Mg-Al LDH surface to generate highly active bifunctional Lewis acid-Bronsted base sites. (3) Above 5 wt%, the excess Cr3+ species generate inert Mg-Cr and/or Mg-Al-Cr LDH-like composites. They are deposited on some active sites, leading to decreased activity. The results show that furfural yields vary significantly in accordance with Cr loadings and that the 5 wt% Cr/Mg-Al LDH achieved the highest value (59% yield, 18 h) because the most effective interaction between the Lewis acidic Cr3+ oxide and the Mg-Al LDH basic site is observed at 5 wt% Cr loading.