Characterization of thermally stable Bronsted acid sites on alumina-supported niobium oxide after calcination at high temperatures

Characterization of thermally stable Bronsted acid sites on alumina-supported niobium oxide after calcination at high temperatures
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高温煅烧后氧化铝负载氧化铌上热稳定布朗斯台德酸位的表征

DOI：
10.1002/cphc.201300189
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发表时间：
2013
期刊：
ChemPhysChem
影响因子：
2.9
通讯作者：
and Tsunehiro Tanaka
and Tsunehiro Tanaka
中科院分区：
化学3区
文献类型：
--
作者：
Tomoyuki Kitano;Tetsuya Shishido;Kentaro Teramura;and Tsunehiro Tanaka

文献摘要

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在氧化铝负载的Nb_2O_5/Al_2O_3催化剂上，通过高温焙烧(如1123K)产生了热稳定的BrO_2O_3酸中心。傅立叶变换红外光谱、电子显微镜、扫描电子显微镜和能量色散X射线(EDX)分析结果表明，当Nb_2O_5的负载量较低时(如5wt %)，Nb_2O_5单层晶格高度分散在氧化铝上，没有出现B_2O_3酸中心。随着Nb_2O_5负载量的增加，Nb_2O_5单层结构域在Al_2O_3表面的覆盖率增加，当负载量为16wt %时，复盖率几乎达到全覆盖。在该负载量水平下，作为布朗斯特酸中心的羟基的数量急剧增加。酸性质与材料结构之间的关系表明，在Nb2O5单分子膜结构域之间形成的桥羟基(NbO(H)Nb)起着热稳定的Brnsted酸中心的作用。
Thermally stable Brønsted acid sites were generated on alumina‐supported niobium oxide (Nb2O5/Al2O3) by calcination at high temperatures, such as 1123 K. The results of structural characterization by using Fourier‐transform infrared (FTIR) spectroscopy, TEM, scanning transmission electron microscopy (STEM), and energy‐dispersive X‐ray (EDX) analysis indicated that the Nb2O5monolayer domains were highly dispersed over alumina at low Nb2O5loadings, such as 5 wt %, and no Brønsted acid sites were presents. The coverage of Nb2O5monolayer domains over Al2O3increased with increasing Nb2O5loading and almost‐full coverage was obtained at a loading of 16 wt %. A sharp increase in the number of hydroxy groups, which acted as Brønsted acid sites, was observed at this loading level. The relationship between the acidic properties and the structure of the material suggested that the bridging hydroxy groups (NbO(H)Nb), which were formed at the boundaries between the domains of the Nb2O5monolayer, acted as thermally stable Brønsted acid sites.