A Study of the Feasibility of Incorporation of Chromium into the Molecular Sieve Framework: The Transformation of 1-Butene over Cr-Silicoaluminophosphate Molecular Sieves

Computational Study of the Structural and Electronic Properties of Dopant Ions in Microporous AlPOs. 2. Redox Catalytic Activity of Trivalent Transition Metal Ions

“…The Cr III dopant does not follow this trend, and its replacement energy is much higher than expected from its ionic radius, which can be attributed to the instability of Cr III in tetrahedral coordination, as confirmed by the scarcity of inorganic complexes with tetrahedral Cr III . The crystal field stabilization energy of octahedral and tetrahedral Cr III has been estimated for oxides with the spinel structure. , The resulting values are 2.33 eV for octahedral Cr III and 0.69 eV for tetrahedral Cr III , with a difference of 1.64 eV. This value has the same order of magnitude as the energy difference of ∼1.20 eV required in our calculations for bringing the replacement energy Δ E III of Cr III in AlPO-34 in line with the trend observed for the other Me III dopants.…”

Transition-Metal Ions in Aluminophosphate and Silicoaluminophosphate Molecular Sieves: Location, Interaction with Adsorbates and Catalytic Properties

“…In the patent literature 28 the synthesis of CrAPO-5 has been reported, but the remaining question concerns the possibility and the extent of tetrahedral Cr(III) substitution for Al 3+ in the framework. Isomorphous substitution requires tetrahedral coordination of Cr(III), which is very rare in inorganic complexes because the crystal field stabilization energy of octahedral Cr(III) (224.5 kJ/mol) is much greater than that for tetrahedral Cr(III) (66.9 kJ/mol). , Therefore, tetrahedral coordination of Cr(III) in aluminophosphates should be difficult to achieve. Although several papers report the synthesis of chromium-containing AlPOs and their application as advanced materials, − only limited effort was made to characterize these materials.…”

Synthesis and Characterization of Mesoporous Chromium-Containing Silica Tube Molecular Sieves CrMCM-41

“…Chromium compounds have been widely used as catalysts for selective oxidation of various organic substrates. , Chromium-containing molecular sieves have attracted catalytic interest. − Several chromium-containing molecular sieves such as CrS-1, , Cr-β, CrAPSO-5, ,, CrAPSO-11, , and CrAPSO-34 have been synthesized and characterized. However, these molecular sieves are microporous solids with channels less than 10 Å which are too small for the oxidation of large organic molecules.…”