Structural characterization of Co- and Si-substituted AlPO-34 synthesized in the presence of morpholine

SAPO-34, CoAPO-34 and CoAPSO-34 materials, synthesized using morpholine as structure directing agent, were structurally characterized by single-crystal and X-ray powder diffraction (XRD) data. HF was also used for the crystallization of CoAPO-34. The incorporation of Co and/or Si atoms in the framework sites was determined by different routes in the structure refinement. In CoAPO-34, at room temperature one of the Al framework sites was sixfold-coordinated with four O and two F atoms. Fluorine bridged two Al atoms. The loss of fluorine occurred at around 450°C and restored the tetrahedral coordination of the 6-coordinated Al atom. In agreement with TGA analysis, the presence of two morpholine molecules in each cage of all these chabazite-type materials was assessed by structural studies. -NH₂ vibrations in the IR spectra of assynthesized samples indicated that some morpholine molecules are protonated and act as counterbalancing charges of the negative framework. Structural modifications under heating, followed by in-situ high temperature XRD, showed that CoAPO-34 materials start to lose crystallinity at around 730°C. Bridging hydroxyls [Co²⁺-O(H)-P] were found by FTIR, and the presence of tetrahedral Co²⁺ ions was inferred by UV-Vis-NIR spectroscopy.