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 450degreesC 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 as-synthesized 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 730degreesC. Bridging hydroxyls [Co2+-O(H)-P] were found by FTIR, and the presence of tetrahedral Co2+ ions was inferred by UV-Vis-NIR spectroscopy.