Development of an ESR technique for testing sulfated zirconia catalysts

Bedilo, Alexander F.; Ivanova, A. S.; Пахомов, Н. А.; Volodin, Alexander M.

doi:10.1016/s1381-1169(00)00114-x

Cited by 27 publications

(19 citation statements)

References 10 publications

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“…The spectrometer operation and analysis of the obtained results were performed using a PC and the software package EPR‐CAD. The concentration of paramagnetic Ti 3+ ions was found using a standard ESR procedure of double integration of the spectra with the zero‐line correction, which was used in earlier work . 2,2‐Diphenyl‐1‐picrylhydrazyl and a solution of Cu(acac) 2 in the mixture of toluene:chloroform = 1:1 were used as the standards for calibration.…”

Section: Methodsmentioning

confidence: 99%

Formation of Isolated Titanium(III) Ions as Active Sites of Supported Titanium–Magnesium Catalysts for Polymerization of Olefins

Mikenas

Koshevoy

Захаров

et al. 2014

Macro Chemistry & Physics

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Electron spin resonance (ESR) studies reveal a high yield of isolated Ti3+ compounds (30–70% of the total titanium content) that form in superactive supported titanium–magnesium catalysts (TMCs) of composition TiCl4/MgCl2 with a low titanium content (≤0.1 wt%) after their interaction with different aluminum trialkyls (AlR3). These catalysts strongly differ from conventional TMCs with titanium contents of 1–3 wt%, which produce a set of isolated or associated Ti(II) and Ti(III) species after the interaction with the AlR3. A correlation is found between the content of the isolated Ti(III) ions and the activity in ethylene polymerization. According to temperature rising elution fractionation (TREF) data, the catalysts with a low titanium content (isolated Ti(III) ions) mainly produce polypropylene with a very high atactic‐fraction content. Organic products formed on the interaction of AlEt3 and AlMe3 with TMC are identified. The data obtained allow a scheme of Ti3+ and Ti2+ compounds formed in these catalysts to be proposed.

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Section: Methodsmentioning

confidence: 99%

Formation of Isolated Titanium(III) Ions as Active Sites of Supported Titanium–Magnesium Catalysts for Polymerization of Olefins

Mikenas

Koshevoy

Захаров

et al. 2014

Macro Chemistry & Physics

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show abstract

“…This paper continues a series of our publications devoted to detailed investigation of sulfated zirconia catalysts by means of in situ ESR. 8,[21][22][23][24][25][26][27] While the focus of attention in most of these earlier publications was the study of strong surface one-electron acceptor sites that are unique for sulfated zirconia and other similar materials, now we turn our attention to O 2 À radical anions that were mentioned only briefly by us before. 8,22 Despite the fact that we found their appearance very common for sulfated zirconia, the literature lacks any systema-tic data on their formation, structure and properties on the surface of this material.…”

Section: Introductionmentioning

confidence: 99%

Superoxide radical anions on the surface of zirconia and sulfated zirconia: formation mechanisms, properties and structure

Bedilo

Plotnikov

Mezentseva

et al. 2005

Phys. Chem. Chem. Phys.

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In situ ESR spectroscopy has been used for direct comparison of different thermal and light-induced processes leading to generation of superoxide radical anions on the surface of various zirconia and sulfated zirconia materials. For materials of both types the magnetic resonance parameters of the radical anions were found to be practically independent of the generation method, except for oxygen coadsorption with NO that yields radicals with somewhat smaller gz values. The parameters appear to depend mostly on the state of the surface zirconia cations stabilizing the radical anions, so that the g tensor anisotropy is significantly smaller over sulfated zirconia. It is shown that light-induced formation of superoxide radical anions in the presence of coadsorbed hydrocarbons can be initiated with visible light. Original SIET reaction mechanisms are suggested for the formation of superoxide radical anions by coadsorption with hydrocarbons and illumination after such coadsorption to extend the previously known ones to account for the observed phenomena. Cluster model DFT calculations of magnetic resonance parameters of O2- radical anions stabilized on the surface of zirconium dioxide showed that the adsorption complexes have a -shape rather than linear structure. The magnetic resonance parameters obtained by calculations practically match experimental data and adequately describe their changes after the surface modification with sulfates.

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“…Earlier direct correlations were observed between the concentrations of such sites and the catalytic activity in low-temperature CO oxidation, n-butane isomerization and ethanol dehydration. 32,54,55 A strong signal of TNB radical anions characterized by anisotropic splitting on a nitrogen atom with A zz = 27.2 G was observed on the AP-MgO sample after activation in nitrogen flow without any reaction. 56 Its intensity on activated AP-MgO before reaction was about 6×10 18 g -1 .…”

Section: Characterization Of Electron-donor and Electron-acceptor Sitmentioning

confidence: 96%

“…The EPR experiments were conducted using the EPR installation described in detail elsewhere. 32 An ERS-221 spectrometer was used for registration of the X-band ESR spectra at room temperature. The concentrations of the paramagnetic species were determined by numerical double integration with baseline compensation.…”

Section: Introductionmentioning

confidence: 99%

Study of MgO transformation into MgF2 in the presence of CF2Cl2•

Vedyagin

Bedilo

Mishakov

et al. 2017

JSCS

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Alkaline-earth metal oxide aerogels prepared by sol-gel method followed by autoclave drying are nanocrystalline mesoporous materials with high reactivity. Bulk solid-state reaction of MgO aerogels with CF 2 Cl 2 takes place after a long induction period, during which the active sites are accumulated on the surface of the nanoparticles. It was found that vanadium addition has a promoting effect on this reaction accelerating the process of the active sites formation. A method for characterization of electron-acceptor sites by electron spin resonance spectroscopy using perylene as the spin probe was developed. A good correlation was observed between the rate of the CF 2 Cl 2 destructive sorption and the concentration of weak electron-acceptor sites. Simplified models of such sites were suggested. The acid sites on the modified MgO surface were supposed to be originated from separation of the charged fragments resulting in the surface polarization. Uncompensated oxygen substitution for chlorine and/or fluorine ions leads to appearance of Lewis acid sites while HCl/HF chemisorption results in Bronsted acid sites formation.

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Development of an ESR technique for testing sulfated zirconia catalysts

Cited by 27 publications

References 10 publications

Formation of Isolated Titanium(III) Ions as Active Sites of Supported Titanium–Magnesium Catalysts for Polymerization of Olefins

Formation of Isolated Titanium(III) Ions as Active Sites of Supported Titanium–Magnesium Catalysts for Polymerization of Olefins

Superoxide radical anions on the surface of zirconia and sulfated zirconia: formation mechanisms, properties and structure

Study of MgO transformation into MgF2 in the presence of CF2Cl2•

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