Structure of the Catalytic Active Sites in Vanadium-Doped Aluminophosphate Microporous Materials. New Evidence from Spin Density Studies

Maurelli, Sara; Berlier, Gloria; Chiesa, Mario; Musso, Federico; Corà, Furio

doi:10.1021/jp505896x

Cited by 23 publications

(34 citation statements)

References 76 publications

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“…The 27 Al signal is consistent with a hyperfine interaction dominated by the isotropic Fermi contact contribution ( a iso ), ranging between 5 and 20 MHz (Table S1). Such isotropic couplings provide a unique and direct confirmation for the presence of Ti 3+ −Cl−Al linkages, corresponding to a spin density transfer in the 3 s Al orbital in the range of 0.15–0.60 %, which is significantly larger than that observed for other systems involving M(3d 1 )−L−Al linkages …”

Section: Figurementioning

confidence: 66%

Unraveling the Catalytic Synergy between Ti³⁺ and Al³⁺ Sites on a Chlorinated Al₂O₃: A Tandem Approach to Branched Polyethylene

et al. 2016

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An original step‐by‐step approach to synthesize and characterize a bifunctional heterogeneous catalyst consisting of isolated Ti3+ centers and strong Lewis acid Al3+ sites on the surface of a chlorinated alumina has been devised. A wide range of physicochemical and spectroscopic techniques were employed to demonstrate that the two sites, in close proximity, act in a concerted fashion to synergistically boost the conversion of ethylene into branched polyethylene, using ethylene as the only feed and without any activator. The coordinatively unsaturated Al3+ ions promote ethylene oligomerization through a carbocationic mechanism and activate the Ti3+ sites for the traditional ethylene coordination polymerization.

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Section: Figurementioning

confidence: 66%

Unraveling the Catalytic Synergy between Ti³⁺ and Al³⁺ Sites on a Chlorinated Al₂O₃: A Tandem Approach to Branched Polyethylene

et al. 2016

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“…These values nicely correlates with values recently observed by some of us in the case of VO 2? -O-Al linkages in V doped alumino-phosphate materials [67]. Considerations analogous to those described in the case of Si allow inferring a spin density in the Al 3 s orbital of the order of 0.16 % consistent with the spin density transfer over the Si framework.…”

Section: Reduced Ti Species In Ets-10mentioning

confidence: 77%

Rational Design of Engineered Multifunctional Heterogeneous Catalysts. The Role of Advanced EPR Techniques

et al. 2015

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The importance of surface paramagnetic species owes much to that of surface phenomena which are involved in numerous areas of chemistry and material science such as heterogeneous catalysis, photochemistry and, in general terms, nano-sciences and technology. In the present contribution the opportunities offered by the use of EPR in the field of heterogeneous catalysis, with emphasis on the application of hyperfine techniques, will be illustrated taking as an example Ti-based catalytic materials. The reductive activation of framework titanium ions in the different materials and their sub-sequent reactivity towards NH 3 is followed, highlighting subtle differences in chemical reactivity related to the different matrixes.

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“…Both time intervals T 1 and T 2 were incremented in 16 ns from the starting value of 96 ns. Q-band HYSCORE experiments were implemented using the remote detection technique [32] to avoid blind spot effects. The remote-echo detector sequence π/2t r -π/2 -τ r -πτ recho was added at the end of the HYSCORE sequence, with t π/ 2 = 16 ns, τ r = 200 ns, and t r = 3 μs.…”

Section: Characterization Techniquesmentioning

confidence: 99%

“…Under these circumstances the nuclear Zeeman interaction dominates (A < 2ν I ) and an extended ridge, with maximum extension of approximately 20 MHz, centered at ν P is observed, in the (+,+) quadrant. In order to avoid blind spot effects the remote detection technique was used and, since only part of the correlation pattern is observed due to the limited excitation bandwidth, experiments at different magnetic field settings were performed [32]. Inspection of Fig.…”

Section: H G βH S G β H S H S a I S A I S I Smentioning

confidence: 99%

Synthesis and structural characterization of a new SbPO4-GeO2 glass system

Montesso

Manzani

Donoso

et al. 2018

Journal of Non-Crystalline Solids

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This work presents the production and characterization of a new prolific binary glass system based on SbPO 4-GeO 2. The dependence of GeO 2 content on thermal, structural and optical properties were investigated by means of thermal analysis, Raman, UV-Vis-NIR, infrared, M-lines and EPR spectroscopy. Glass transition temperatures remain constant around 410°C when GeO 2 content is increased, indicating that GeO 4 units are not responsible for increasing the connectivity of PO 4 units. Thermal stability linearly increases as a function of GeO 2 content, reaching a value around 400°C for glass containing 90 mol% of GeO 2. Raman spectroscopy was used to evaluate the glass structural changes when GeO 2 is incorporated from 30 to 90 mol% indicating a gradual change from a phosphate to a germanate glass skeleton. The optical window extends from 350 nm at UV region, up to 2.7 μm in the middle-infrared region limited by the multiphonon cutoff due to the strong OH absorption. M-lines technique shows that increasing GeO 2 content decreases the refractive index, mainly because the lower concentration of higher polarizable antimony atoms. EPR spectra of heat treated V 2 O 5 doped glasses, at different temperatures above the glass transition temperature, shows the characteristic eight-line hyperfine splitting spectrum. The spin Hamiltonian parameters obtained from the simulated spectra indicates that the paramagnetic tetravalent vanadium ions in the glasses exist as vanadyl form VO 2+ , located in axially distorted octahedral sites. For glasses treated at higher temperatures a second VO 2+ component appears in the EPR spectra and the analysis of the spin-Hamiltonian parameters suggests that these vanadyl ions are in more tetragonal distorted octahedral sites than those in the glass.

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Structure of the Catalytic Active Sites in Vanadium-Doped Aluminophosphate Microporous Materials. New Evidence from Spin Density Studies

Cited by 23 publications

References 76 publications

Unraveling the Catalytic Synergy between Ti³⁺ and Al³⁺ Sites on a Chlorinated Al₂O₃: A Tandem Approach to Branched Polyethylene

Unraveling the Catalytic Synergy between Ti³⁺ and Al³⁺ Sites on a Chlorinated Al₂O₃: A Tandem Approach to Branched Polyethylene

Rational Design of Engineered Multifunctional Heterogeneous Catalysts. The Role of Advanced EPR Techniques

Synthesis and structural characterization of a new SbPO4-GeO2 glass system

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Structure of the Catalytic Active Sites in Vanadium-Doped Aluminophosphate Microporous Materials. New Evidence from Spin Density Studies

Cited by 23 publications

References 76 publications

Unraveling the Catalytic Synergy between Ti3+ and Al3+ Sites on a Chlorinated Al2O3: A Tandem Approach to Branched Polyethylene

Unraveling the Catalytic Synergy between Ti3+ and Al3+ Sites on a Chlorinated Al2O3: A Tandem Approach to Branched Polyethylene

Rational Design of Engineered Multifunctional Heterogeneous Catalysts. The Role of Advanced EPR Techniques

Synthesis and structural characterization of a new SbPO4-GeO2 glass system

Contact Info

Product

Resources

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Unraveling the Catalytic Synergy between Ti³⁺ and Al³⁺ Sites on a Chlorinated Al₂O₃: A Tandem Approach to Branched Polyethylene

Unraveling the Catalytic Synergy between Ti³⁺ and Al³⁺ Sites on a Chlorinated Al₂O₃: A Tandem Approach to Branched Polyethylene