Synthesis, Characterization, and Catalytic Performance of Cr-Incorporated Aluminoborate Octahedral Molecular Sieves

Identification of key oxidative intermediates and the function of chromium dopants in PKU-8: catalytic dehydrogenation of sec-alcohols with tert-butylhydroperoxide

t-BuOO* activated by Cr-PKU-8 from TBHP is the key intermediate to the highly selective dehydrogenation of sec-alcohols.

Continuous solid solutions constructed from two isostructural octahedron-based molecular sieves: preparation, acidity regulation and catalytic application in Strecker reactions

Al_xGa_1−x-PKU-1 solid solutions were used as acidity-tunable solid acids to catalyze the nucleophilic addition of the cyanide anion to imines.

Extending Unique 1D Borate Chains to 3D Frameworks by Introducing Metallic Nodes

Two novel alkali/alkaline-earth borates, Ba₆ [B₆ O₉ (OH)₆ ]₂ (H₃ BO₃ ) (1) and Li₇ MAlB₁₂ O₂₄ (M=Ba, Sr, Ca) (2 a-c), with 1D and 3D structures have been made hydrothermally and characterized. 1 features a rare 1D anionic chain built by hexaborate clusters of B₆ O₁₁ (OH)₆ ; each made of six BO₄ /BO₂ (OH)₂ tetrahedra. The anionic chains are embedded in the channels of a Ba₆ -based wheel-cluster open-framework. On the basis of the structural analyses of 1, by incorporating Al atoms as the linkers and tuning the reaction conditions, the novel anhydrous 3D aluminoborates (ABOs) 2 a-c have been successfully obtained, constructed from B₆ O₁₄ -based cluster chains and AlO₆ octahedra. The 3D ABO framework and 3D Ba-O-Li network are interpenetrated to give a final dense structure. The study not only realized the expansion of the structure from the 1D chain of 1 to the 3D dense ABOs 2 a-c, but also obtained the first 3D AlO₆ -containing ABOs made under hydrothermal conditions. Different from the previously known 4-connected zeolite-type ABOs, alternately arranged from AlO₄ tetrahedra and oxo-boron clusters, the AlO₆ octahedra in 2 a-c as the linkers join to six 1D B₆ O₁₄ -based cluster chains to produce 3D ABOs. The optical diffuse reflectance spectra reveal that 2 a-c have wide range transparency. In addition, the thermal property analysis proves that 2 a-c are congruently melting compounds and possess high thermostability.

Octahedron-based gallium borates (Ga-PKU-1) with an open framework: acidity, catalytic dehydration and structure–activity relationship

The octahedron-based Ga-PKU-1 catalyst with an open framework acted as an efficient solid acid catalyst for isopropanol decomposition.

Systematic study of Cr3+ substitution into octahedra-based microporous aluminoborates

Single crystals of pure aluminoborate PKU-1 (Al3B6O11(OH)5·nH2O) were obtained, and the structure was redetermined by X-ray diffraction. There are three independent Al atoms in the R3 structure model, and Al3 locates in a quite distorted octahedral environment, which was evidenced by (27)Al NMR results. This distortion of Al3O6 octahedra release the strong static stress of the main framework and leads to a symmetry lowering from the previously reported R3 to the presently reported R3. We applied a pretreatment to prepare Al(3+)/Cr(3+) aqueous solutions; as a consecquence, a very high Cr(3+)-to-Al(3+) substitution content (∼50 atom %) in PKU-1 can be achieved, which is far more than enough for catalytic purposes. Additionally, the preference for Cr(3+) substitution at the Al1 and Al2 sites was observed in the Rietveld refinements of the powder X-ray data of PKU-1:0.32Cr(3+). We also systematically investigated the thermal behaviors of PKU-1:xCr(3+) (0 ≤ x ≤ 0.50) by thermogravimetric-differential scanning calorimetry, in situ high-temperature XRD in vacuum, and postannealing experiments in furnace. The main framework of Cr(3+)-substituted PKU-1 could be partially retained at 1100 °C in vacuum. When 0.04 ≤ x ≤ 0.20, PKU-1:xCr(3+) transferred to the PKU-5:xCr(3+) (Al4B6O15:xCr(3+)) structure at ∼750 °C by a 5 h annealing in air. Further elevating the temperature led to a decomposition into the mullite phase, Al4B2O9:xCr(3+). For x > 0.20 in PKU-1:xCr(3+), the heat treatment led to a composite of Cr(3+)-substituted PKU-5 and Cr2O3, so the doping upper limit of Cr(3+) in PKU-5 structure is around 20 atom %.