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 %.