Stability of the Co(II) valence state in aluminophosphate-5 molecular sieve to calcination from low temperature electron spin resonance

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

“…Temperature-programmed desorption (TPD) and thermogravimetric analysis (TGA) of amine probe molecules show that Co(II) at low concentrations is present in lattice positions and generates discrete Brønsted sites in a concentration equal to the cobalt content in both as-synthesized blue CoAPO-5 and calcined yellow-green CoAPO-5 consistent with no oxidation associated with the color change . On the basis of this finding, Kurshev et al , performed ESR experiments from 7 to 34 K. The experimental data in this temperature range show that the ESR signal of Co(II) in calcined CoAPO-5 does not follow the Curie law and therefore that the ESR intensity of calcined samples is not directly associated with the amount of paramagnetic cobalt. The intensity of the doubly integrated spectra as a function of the temperature of as-synthesized and calcined CoAPO-5 is displayed in Figure .…”

Local Environment of Phosphorus Atoms in CoAPO4-n Molecular Sieves: A 31P NMR Study

“…A nice example has been recently published by Barrett et al on four different CoAPO 4 - n that shows the power of the method to access the local structure around Co atoms. Diffuse reflectance electronic absorption spectroscopy (DREAS) and electron spin resonance (ESR) have also been applied to the study of the redox properties of CoAPO 4 - n molecular sieves. , These techniques yield oxidation state and coordination of Co species in the material. However, the discrimination between framework and extraframework species is not trivial as tetrahedrally coordinated Co species have also been observed in AlPO 4 - n materials impregnated with cobalt salts …”