10.1021/ic500352g.s002
Qiaoqi Li
Qiaoqi
Li
Cong Lin
Cong
Lin
Zhengyang Zhou
Zhengyang
Zhou
Jing Ju
Jing
Ju
Guobao Li
Guobao
Li
Jianhua Lin
Jianhua
Lin
Wenliang Gao
Wenliang
Gao
Rihong Cong
Rihong
Cong
Tao Yang
Tao
Yang
Systematic Study of Cr<sup>3+</sup> Substitution into
Octahedra-Based Microporous Aluminoborates
American Chemical Society
2014
Al 2 sites
mullite phase
Al 3B
heat treatment
Al 4B
Al 3
Al 1
R 3.
postannealing experiments
octahedral environment
Rietveld refinements
R 3 structure model
aluminoborate PKU
XRD
Al 4B structure
27 Al NMR results
Al atoms
Systematic Study
5 h annealing
Cr 2O
Al 3O octahedra release
2014-06-02 00:00:00
Dataset
https://acs.figshare.com/articles/dataset/Systematic_Study_of_Cr_sup_3_sup_Substitution_into_Octahedra_Based_Microporous_Aluminoborates/2287324
Single crystals of pure aluminoborate
PKU-1 (Al<sub>3</sub>B<sub>6</sub>O<sub>11</sub>(OH)<sub>5</sub>·<i>n</i>H<sub>2</sub>O) were obtained, and the structure was redetermined
by X-ray diffraction. There are three independent Al atoms in the <i>R</i>3 structure model, and Al3 locates in a quite distorted
octahedral environment, which was evidenced by <sup>27</sup>Al NMR
results. This distortion of Al3O<sub>6</sub> octahedra release the
strong static stress of the main framework and leads to a symmetry
lowering from the previously reported <i>R</i>3̅ to
the presently reported <i>R</i>3. We applied a pretreatment
to prepare Al<sup>3+</sup>/Cr<sup>3+</sup> aqueous solutions; as a
consecquence, a very high Cr<sup>3+</sup>-to-Al<sup>3+</sup> substitution
content (∼50 atom %) in PKU-1 can be achieved, which is far
more than enough for catalytic purposes. Additionally, the preference
for Cr<sup>3+</sup> substitution at the Al1 and Al2 sites was observed
in the Rietveld refinements of the powder X-ray data of PKU-1:0.32Cr<sup>3+</sup>. We also systematically investigated the thermal behaviors
of PKU-1:<i>x</i>Cr<sup>3+</sup> (0 ≤ <i>x</i> ≤ 0.50) by thermogravimetric–differential scanning
calorimetry, in situ high-temperature XRD in vacuum, and postannealing
experiments in furnace. The main framework of Cr<sup>3+</sup>-substituted
PKU-1 could be partially retained at 1100 °C in vacuum. When
0.04 ≤ <i>x</i> ≤ 0.20, PKU-1:<i>x</i>Cr<sup>3+</sup> transferred to the PKU-5:<i>x</i>Cr<sup>3+</sup> (Al<sub>4</sub>B<sub>6</sub>O<sub>15</sub>:<i>x</i>Cr<sup>3+</sup>) structure at ∼750 °C by a 5 h annealing
in air. Further elevating the temperature led to a decomposition into
the mullite phase, Al<sub>4</sub>B<sub>2</sub>O<sub>9</sub>:<i>x</i>Cr<sup>3+</sup>. For <i>x</i> > 0.20 in PKU-1:<i>x</i>Cr<sup>3+</sup>, the heat treatment led to a composite
of Cr<sup>3+</sup>-substituted PKU-5 and Cr<sub>2</sub>O<sub>3</sub>, so the doping upper limit of Cr<sup>3+</sup> in PKU-5 structure
is around 20 atom %.