An Investigation of Framework Substitution of Cobalt into Aluminophosphate-5 Using Electron Spin Resonance and Temperature-Programmed Desorption Measurements

Kurshev, Vadim; Kevan, Larry; Parillo, D. J.; Pereira, Clairton Marcolongo; Kokotailo, G. T.; Gorte, Raymond J.

doi:10.1021/j100091a035

Cited by 95 publications

(70 citation statements)

References 3 publications

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“…Our observation is in line with those of Kurshev et al, 11 Pereira et al, 12 and Berndt et al 13 that only a small fraction of Co 2+ is oxidized during calcination. This observation is not in full agreement with the results of Thomson et al 30 The observed change in ESR parameters and line shape of the Co 2+ ESR signal clearly indicates a change in the coordination geometry upon calcination, but it is not necessary to postulate the extreme distortion causing negative zero-field splitting (2|D| ) -13 cm -1 ) and a non-Curie-Weiss behavior as proposed by Kurshev et al 11 Thus, in contrast to Kurshev et al, 11 we found a zero field splitting ∆ ) 2|D| ) 7 cm -1 , and a normal ESR temperature dependency for both the assynthesized and calcined CoAPO-n material. The latter has also been observed by Thomson et al 30 This confirms that the results of Kurshev et al 11 cannot be reproduced.…”

Section: Discussionsupporting

confidence: 94%

“…The observed decrease of signal intensity with 30% is significant, knowing that the absolute and relative error for ESR quantifications are estimated to be about 20% and 5-10%, respectively. 25,26 These results confirm those of Kurshev et al, 11 Pereira et al, 12 and Berndt et al 13 that only a small fraction of Co 2+ is oxidized to Co 3+ during calcination.…”

Section: Esr Signals Of Cosupporting

confidence: 68%

“…In any case, the observed effective g values are comparable to those previously found for CoAPO-5 and CoAPO-41 and comparable with those of relevant reference compounds (Table 2). 8,11,[20][21][22][23][24] After calcination, the overall ESR signal intensity decreases and the perpendicular component of the broad, axially symmetric signal shifts to 5.44 ( Figure 1B).…”

Section: Methodsmentioning

confidence: 99%

“…Lee and Chon proved the oxidative abilities of calcined CoAPO-5 and CoAPO-11 with ESR by the formation of radicals from alkenes. 10 However, this oxidation-reduction behavior of CoAPO-5 materials has been challenged by Kurshev et al 11 They observed an unusual temperature-dependent behavior for the Co 2+ ESR signal of calcined CoAPO-5 (non Curie-Weiss behavior) in comparison with the as-synthesized CoAPO-5 material (CurieWeiss behavior) between 4 and 20 K, and accordingly, a zerofield splitting ∆ of -13 cm -1 was determined for the calcined material. This observation was explained by a distortion of tetrahedral Co 2+ to dihedral symmetry resulting from the interaction with two O 2 molecules.…”

Section: Introductionmentioning

confidence: 99%

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Electron Spin Resonance of High-Spin Cobalt in Microporous Crystalline Cobalt-Containing Aluminophosphates

et al. 1999

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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 Curie-Weiss behavior for both as-synthesized and calcined samples confirming (a) the m s ) ( 1/2 ground state of magnetically isolated high-spin cobalt and (b) a zero field splitting ∆ > 0 cm -1 . Quantitation of the ESR signals indicated that most of the Co 2+ is ESR active and that only about 30% of this Co 2+ can be oxidized to the ESR-inactive Co 3+ after calcination. The spin Hamiltonian parameters of as-synthesized and calcined CoAPO-5 material, as determined by spectrum simulation and the microwave power saturation technique, support the presence of framework Co 2+ in a flattened or elongated tetrahedron (D 2d ).

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Section: Discussionsupporting

confidence: 94%

Section: Esr Signals Of Cosupporting

confidence: 68%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Electron Spin Resonance of High-Spin Cobalt in Microporous Crystalline Cobalt-Containing Aluminophosphates

et al. 1999

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“…Apart from usual techniques such as XRD, TG and FT-IR [18,19], a variety of spectroscopic methods including DRUV-VIS [19] and EPR [20] were employed to probe the location and oxidation of state of cobalt in the aluminophosphate matrix. Beyond the spectroscopic investigation, reactivity assessment is an important method to probe the cobalt sites.…”

Section: Introductionmentioning

confidence: 99%

Probing Cobalt Sites in CoAPO-11 via Spectroscopic and Activity Studies

Sahoo¹,

Badamali²

2017

Asian J. Chem.

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A systematic study undertaken for the oxidation state, coordination, stability of cobalt in CoAPO-11 structure by means of spectroscopic and catalytic activity, is presented. AlPO-11 containing Co(II) in the tetrahedral coordination was indicated by powder diffraction, electronic and EPR data. During calcination of Co(II) was partly converted to Co(III) and reverted back to Co(II) upon exposure to atmosphere. Apart from micropores, CoAPO-11 sample contains mesopores, which possibly arise from interparticle void space. The tetrahedral location of Co(II) was inferred from EPR data. The rectangular to spherical shapes of CoAPO-11 material was evident from electron micrographs. Activity studies revealed that o-cresol can selectively be converted to o-hydroxy benzoic acid. Moderate activity of CoAPO-11 along with spectroscopic analysis supports the fact that Co(II) is predominantly located in tetrahedral framework and do not convert to Co(III) effectively, as a consequence Co(II) are stable and do not display appreciable oxidative ability under mild reaction conditions.

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Transition Metal Ions in Microporous Crystalline Aluminophosphates: Isomorphous Substitution

Weckhuysen¹,

Rao

Martens

et al. 1999

Eur. J. Inorg. Chem.

122

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Microporous crystalline metalloaluminophosphates (MeAPO‐n) represent an important group of molecular sieves because of their potential catalytic and adsorptive properties. Many transition metal ions are claimed to incorporate in the framework of these molecular sieves. Here, the concept of isomorphous substitution, and the different indirect and direct tools available to verify this substitution process for Co, Cr, V, Fe and Mn are reviewed taking the AlPO4‐5 structure as an example. In addition, it will be shown that transition metal ions can be used as a probe to follow the hydrothermal synthesis process of microporous aluminophosphates.

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An Investigation of Framework Substitution of Cobalt into Aluminophosphate-5 Using Electron Spin Resonance and Temperature-Programmed Desorption Measurements

Cited by 95 publications

References 3 publications

Electron Spin Resonance of High-Spin Cobalt in Microporous Crystalline Cobalt-Containing Aluminophosphates

Electron Spin Resonance of High-Spin Cobalt in Microporous Crystalline Cobalt-Containing Aluminophosphates

Probing Cobalt Sites in CoAPO-11 via Spectroscopic and Activity Studies

Transition Metal Ions in Microporous Crystalline Aluminophosphates: Isomorphous Substitution

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