Abstract:Four highly crystalline, cobalt-containing microporous aluminophosphates have been investigated by using liquid He X-and/or Q-band electron spin resonance (ESR) spectroscopy in order to investigate the coordination of high-spin cobalt before and after calcination. The ESR spectra of the four zeolite structures are characterized by an axial signal with an effective g ⊥ ≈ 5.80-5.44 and g || ≈ 2.00. Quantitative temperature dependence measurements of this axial signal in the temperature range 4-30 K reveal a Cur… Show more
“…Computer simulation has yielded g' 1 g' 2 5.0, g' 3 2.4 and peak-topeak line widths W 1 W 2 27 mT and W 3 90 mT. [67] Several types of high-spin Co II complexes have so far been studied by EPR spectroscopy, [68] and the differences in the EPR pattern between tetrahedral and octahedral Co II have been well documented. [69±72] In tetrahedral Co II , the ground orbital state is 4 A 2 , and thus the orbital angular momentum is well quenched; this makes the spin Hamiltonian approach appropriate.…”
“…Computer simulation has yielded g' 1 g' 2 5.0, g' 3 2.4 and peak-topeak line widths W 1 W 2 27 mT and W 3 90 mT. [67] Several types of high-spin Co II complexes have so far been studied by EPR spectroscopy, [68] and the differences in the EPR pattern between tetrahedral and octahedral Co II have been well documented. [69±72] In tetrahedral Co II , the ground orbital state is 4 A 2 , and thus the orbital angular momentum is well quenched; this makes the spin Hamiltonian approach appropriate.…”
“…One of the most fascinating researches on microporous AlPO 4 -n materials is the process of isomorphous substitution, in which framework Al 3+ and/or P 5+ ions are replaced by e.g. transition metal ions, such as Mn 2+ [3][4][5][6], Fe 3+ [7,8], V 4+ [9][10][11][12][13], Ti 4+ [14,15], Zn 2+ [16,17], Nb 5+ [18], Cr 3+ [19][20][21] and Co 2+ [22][23][24][25][26]. This process can generate Brö nsted acid and redox sites, leading to intriguing shape-selective catalytic performances.…”
Section: Introductionmentioning
confidence: 99%
“…The incorporation of Co 2+ (d 7 ) can be considered as a showcase for these substituted materials since this transition metal ion not only gives the solid an intense blue color and interesting oxidation properties, but also provides convincing spectroscopic evidence for the framework substitution of Co 2+ as obtained with e.g. diffuse reflectance UV-Vis-NIR spectroscopy, electron spin resonance and X-ray absorption spectroscopy [1, 3,[22][23][24][25][26].…”
Series of CoAPO-5, CoAPO-11 and CoAPO-34 molecular sieves have been synthesized starting from a synthesis gel varying in its amount of Co 2+ and type of solvent molecule. Four protonic solvents have been investigated: water, ethanol, ethylene glycol and glycerol. The obtained crystalline materials were characterized with X-ray diffraction; diffuse reflectance UV-Vis-NIR spectroscopy; infrared spectroscopy; elemental analysis; electron microscopy microprobe analysis and thermo-gravimetrical analysis. It was found that the type of solvent has a strong influence on the crystallization behavior and the substitution degree of Co 2+ for Al 3+ in the framework of microporous aluminophosphates. Ethanol, ethylene glycol and glycerol seem to be the best solvents for the synthesis of single-phase and highly crystalline Co-rich CoAPO-34, CoAPO-11 and CoAPO-5 molecular sieves, respectively. By varying the type of solvent molecule, Co content and template amount in the synthesis gel it was possible to increase the substitution degree of framework Co 2+ in microporous aluminophosphates. In this manner, around 10%, 25% and 36% of Al 3+ could be replaced by Co 2+ in the framework of CoAPO-11, CoAPO-5 and CoAPO-34, respectively. These substitution degrees are substantially higher than those for CoAPO materials synthesized in the presence of water.
“…5. These spectra are typical for the isolated Co 2+ ion in powders [26]. The cobalt atoms substitute the zinc atoms and the neutral charge state is Co 2+ (a 3d 7 configuration).…”
Abstract:Structural, morphological and magnetic properties of Zn 1−x Co x O (x = 0 01 and 0 03) powdered materials are presented. XRD studies reveal a wurtzite-type structure, while the formation of a Co 3 O 4 secondary phase was evidenced by Raman spectroscopy. A ferromagnetic behaviour with low Curie temperature was evidenced by Electron Paramagnetic Resonance (EPR) investigation. We suggest that the origin of the ferromagnetism in Zn 1−x Co x O powders is probably due to the presence of the mixed cation valence of Co ions via a double-exchange mechanism rather than the real doping effect.
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