Hydrothermal synthesis of octahedra-based layered niobium oxide and its catalytic activity as a solid acid
Hydrothermal synthesis of octahedra-based layered niobium oxide and its catalytic activity as a solid acid
复制标题
DOI：
10.1039/c4cy00713a
复制
发表时间：
2014-01-01
影响因子：
5
通讯作者：
Ueda, Wataru
中科院分区：
文献类型：
--
作者：
Murayama, Toru;Chen, Junli;Ueda, Wataru
以草酸铌铵为前驱体，采用水热法合成了层状结构的铌氧化物。所合成的氧化铌的X射线衍射图案（Cu-K α）在2 θ = 22.7度和46.2度处显示出特征峰，表明NbO 6八面体在c方向上的线性角共享。从拉曼测量，层状结构类型的铌氧化物是由NbO 6八面体和{Nb 6 O21}五边形单元。在低压（1.0 × 10 ~（-6））下通过N-2吸附证实了微孔的存在，表明a-b平面的排列是{Nb_6O_（21）}单元的晶体结构基元和Nb_2O_3通道的互连，但没有长程有序（变形正交）。铵阳离子和水通过在400 ℃下煅烧从变形的正交铌氧化物中解吸，并形成布朗斯台德酸位点。与其他晶体铌氧化物的催化活性相比，变形的正交铌氧化物作为固体酸显示出高的催化活性。对苯甲醇和苯甲醚烷基化反应的催化活性顺序为：斜方晶系Nb_2O_5> TT-Nb_2 O_5，无定形Nb_2O_5>> T-Nb_2 O_5，烧绿石型Nb_2O_5。
Layered-structure-type niobium oxides were synthesized by the hydrothermal method by using ammonium niobium oxalate as a precursor. The X-ray diffraction pattern (Cu-K alpha) of the synthesized niobium oxide showed characteristic peaks at 2 theta = 22.7 degrees and 46.2 degrees indicating the linear corner-sharing of NbO6 octahedra in the c-direction. From Raman measurements, the layered-structure-type niobium oxide was composed of NbO6 octahedra and {Nb6O21} pentagonal units. The presence of micropores was confirmed by N-2 adsorption at low pressure (1.0 x 10(-6)), indicating that the arrangement of the a-b plane was an interconnection of the crystal structure motifs of {Nb6O21} units and micropore channels but without long-range order (deformed orthorhombic). Ammonium cations and water were desorbed from the deformed orthorhombic niobium oxide by calcination at 400 degrees C, and Bronsted acid sites were formed. The deformed orthorhombic niobium oxide showed high catalytic activity as a solid acid compared to the catalytic activities of other crystalline niobium oxides. The order of catalytic activity for the alkylation of benzyl alcohol and anisole was deformed orthorhombic Nb2O5 > TT-Nb2O5, amorphous Nb2O5 >> T-Nb2O5, pyrochlore Nb2O5.