Acidity, Redox Behaviour and Stability of Coapo Molecular Sieves of Structure Types 5, 11, 34 and 16

Clustering of cobalt in CoAPO-5 molecular sieves

“…In the present case, no intense spinning sidebands were detected, in contrast to the work of Peeters et al [13,14], Prakash et al [20,21], Chen et al [22], Kraushaar et al [18] and Montes et al [4,19]. For CoAPSO-34 and CoAPSO-44 [23] and CoZnPO-SOD [24] and CoMnAPO-34 [25], intense sidebands were also found.…”

“…1 ). Conventional and straightforward 3~p and 27A1 MAS NMR studies on cobalt-substituted AIPOs (CoAPOs) could not be used in the same way as for MAPO-20 [4,17,18] Montes et al [4,19], for example, measured 31p MAS NMR of CoAPO-5. They observed that, compared with A1PO-5, multiple and intense sidebands were present in the spectrum of CoAPO-5.…”

“…They ascribed the observed increase in anisotropy to strong dipolar couplings of phosphorus with paramagnetic cobalt, supporting the view that cobalt primarily substitutes for framework aluminium. Measurements on Co/A1PO-5 (cobalt-impregnated A1PO-5) and Co/A1PO-11, however, also showed an increased anisotropy [13,14,18], so in the case of CoAPOs, chemical shift anisotropy in 3~p MAS NMR as such cannot be used to prove the framework incorporation of cobalt.…”

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

“…They ascribed this increase in anisotropy to strong dipolar coupling of phosphorus with paramagnetic Co(II) and, hence, as evidence for framework incorporation of Co(II) replacing aluminum. The observation of intense sidebands is reported by several authors, ,, while in other studies no such increase indicating increased anisotropy was reported. , However, measurements of impregnated Co/AlPO-5 and Co/AlPO-11 112,55 also showed NMR sidebands consistent with increased anisotropy. Therefore, such increased anisotropy cannot be used as evidence for isomorphous substitution of cobalt into aluminophosphates.…”

“…Diffuse reflectance UV−vis spectroscopy has been frequently employed for the characeterization of cobalt-containing aluminophosphates. ,, As-synthesized CoAPO-5 has been characterized by a triplet at 16 000, 17 300, and 18 500 cm -1 , which corresponds to 625, 578, and 541 nm. ,,,,, These absorptions are interpreted as due to Co(II) in a tetrahedral environment of oxygens in the AlPO framework. After calcination the intensities of these bands are reduced and the band positions shift to 15 500 cm -1 (645 nm), 17 300 cm -1 (578 nm), and 19 500 cm -1 (513 nm).…”