Layered niobic acid with self-exfoliatable nanosheets and adjustable acidity for catalytic hydration of ethylene oxide
Layered niobic acid with self-exfoliatable nanosheets and adjustable acidity for catalytic hydration of ethylene oxide
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DOI：
10.1016/j.jcat.2011.03.026
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发表时间：
2011-06
影响因子：
7.3
通讯作者：
Zhijian Yang;Ye-Fei Li;Qingbin Wu;N. Ren;Yahong Zhang;Zhipan Liu;Yi Tang
中科院分区：
文献类型：
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作者：
Zhijian Yang;Ye-Fei Li;Qingbin Wu;N. Ren;Yahong Zhang;Zhipan Liu;Yi Tang
报道了层状铌酸(HxK1−xNb3O8，x=0-1)催化环氧乙烷(EO)选择水合反应的新型固体酸催化剂。它们是通过简单地焙烧Nb2O5-K2CO3混合物，然后在不同浓度的HNO3溶液中进行离子交换而得到的。在H2O/EO比为8时，当x=0.7时，单甘醇(MEG)的选择性最高可达95%以上，转化率为99%。结合第一性原理密度泛函理论计算和Hammett指示剂法的计算结果，表明合适的酸强度比酸量对MEG选择性的影响更大。此外，在环氧乙烷的水合过程中，层状HNb3O8也发生了自剥离，这是其良好催化性能的另一个重要因素，暴露了Nb3O8-纳米片层中丰富的酸中心。HNb3O8的热稳定性研究也表明，这种层状铌酸的表征和应用方式都是经过精心选择的。
Layered niobic acids (H x K 1− x Nb 3 O 8, x= 0–1) are reported as new solid acid catalysts for the selective hydration of ethylene oxide (EO). They are prepared by simply calcinating Nb 2 O 5–K 2 CO 3 mixture followed by an ion-exchange process in HNO 3 solution of different concentrations. The highest selectivity for monoethylene glycol (MEG) is achieved over 95% with EO conversion of> 99% at x of 0.7 under H 2 O/EO ratio of 8. Combined with the results of first-principles density functional theory calculations and Hammett indicator method, it is revealed that the suitable acid strength is more crucial for MEG selectivity than acid amount. Furthermore, a self-exfoliation of layered HNb 3 O 8 is also found during EO hydration, which proves to be another important factor for its good catalytic performance by exposing the abundant acid sites among the Nb 3 O 8-nanosheets. The thermal stability investigation of HNb 3 O 8 also indicates a careful selection of characterization and application way for this layered niobic acid.