ESR measurements of concentration for strong surface acceptor centers on zeolites and Al2O3 using nitroxide radical TEMPON

Konovalova, T. A.; Volodin, Alexander M.; Чесноков, В. В.; Паукштис, Е. А.; Ечевский, Г. В.

doi:10.1007/bf02075437

Cited by 16 publications

(11 citation statements)

References 3 publications

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“…The present paper reports the results of a comprehensive ESR study of nanocrystalline MgO involving a variety of techniques successfully used earlier for characterization of catalytic materials prepared by more conventional methods. [14][15][16][17][18] Experimental AP-MgO was prepared by an aerogel technique as follows. Mg ribbon was dissolved in methanol to give a 1 M Mg(OCH 3 ) 2 solution.…”

Section: Introductionmentioning

confidence: 99%

ESR study of nanocrystalline aerogel-prepared magnesium oxide

Richards

Volodin

Bedilo

et al. 2003

Phys. Chem. Chem. Phys.

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Section: Introductionmentioning

confidence: 99%

ESR study of nanocrystalline aerogel-prepared magnesium oxide

Richards

Volodin

Bedilo

et al. 2003

Phys. Chem. Chem. Phys.

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“…It has been shown by EPR and IR spectroscopies that the TEMPONE radical can interact selectively with the strongest surface acceptor centres (LAS) on c-alumina and zeolites. 30 The TEMPONE radical contains two donor centres, the and CxO groups. Since the basicity of the CxO NwOg roup is much higher than that of the functionality,31 NwOĩ nteraction of the CxO group with an acceptor surface site is favourable.…”

Section: Resultsmentioning

confidence: 99%

EPR and ENDOR studies of carotenoid–solid Lewis acid interactions

Konovalova¹,

Kispert²

1998

Faraday Trans.

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EPR and ENDOR results provide strong support for the formation of carotenoid radical cations on activated alumina and silicaÈalumina as a consequence of electron transfer from the adsorbed carotenoid molecules to the Lewis acid sites on these surfaces. This assignment is conÐrmed by the correlation between the AlIII Lewis acid site content on the activated surfaces and the maximum concentration of the generated carotenoid radical cations. The results are compared with those obtained for a solution of carotenoid and which serves as a model system. The ENDOR line at ca. 6.5 MHz obtained for the carotenoids AlCl 3 , adsorbed on solid supports and solution, is attributed to the high-frequency feature of a hyperÐne doublet, carotenoidÈAlCl 3 centred about the 27Al Larmor frequency. ENDOR detection of the hyperÐne doublet, instead of the single line at the Larmor frequency, indicates the formation of strong complexes between carotenoid molecules and Lewis acid sites on the surface.

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“…More recently, the chemisorption of organic radicals, e.g, 2,2,6,6-tetramethyl-4-oxypiperidine-1-oxyl (TEMPON), has been employed in conjunction with ESR spectroscopic investigation of the sorbed molecules (Fionov et al 1996; Markaryan and Lunina 1996). The total number of radical molecules sorbed may be estimated either with or without the application of hyperfine structural analysis of the spectra (Konovalova et al 1991;Taranookha 1996, 1997). However, despite these recent innovations, the temperature programmed desorption (TPD) of ammonia still remains in widespread use (Jacobs 1977;Osako et al 1993;Conna 1995).…”

Section: Introductionmentioning

confidence: 99%

“…pyridine protonated by BAS) appears at 1550 errr' while the band arising from the coordination of pyridine with LAS appears at 1450 em" (Ward 1976;Jacobs 1977;Conna and Nieman 1991;Conna 1995). Studies of TEMPON as a tool are confined to LAS only since this radical is only sorbed on these sites (Konovalova et al 1991) while the ammonia TPD method provides a measure of the total number of BAS and LAS (Jacobs 1977;Conna 1995). Thus, each method has its merits and demerits.…”

Section: Introductionmentioning

confidence: 99%

“…This leads to changes in the hyperfine structure of the ESR spectrum and subsequent complication in the interpretation of the results obtained. This latter difficulty can be overcome by the use of a special version of the method which involves the determination of the total number of TEMPON molecules sorbed without the use of hyperfine structural analysis (Konovalova et al 1991;Patrylak and Taranookha 1997).…”

Section: Introductionmentioning

confidence: 99%

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Chemisorption of Lewis Bases on Zeolites – A New Interpretation of the Results

Patrylak

1999

Adsorption Science & Technology

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The chemisorption of pyridine, the 2,2,6,6-tetramethyl-4-oxypiperidine-1-oxyl radical and ammonia on the cationized and decationized forms of X and Y zeolites, as used for the determination of BrSnsted and Lewis acidity using infrared spectroscopy, ESR spectroscopy and the temperature programmed desorption of ammonia, has been investigated. A new approach, based on a detailed quantitative analysis of the experimental data, is proposed. It was found that the sodium cations are not the Lewis acid sites, but that on the outer surface of zeolite crystals such sites correspond to coordinatively unsaturated aluminium atoms. These amount to 17% and 14%, respectively, of the entire surface aluminium for NaX and NaY zeolites. The remaining coordinatively unsaturated aluminium in the heart of a zeolite structure decationized to 84% make little contribution to the overall percentage. It was shown that the temperature programmed desorption of ammonia is the most effective method for providing a quantitative determination of the BrOnsted acidity of zeolites. The overwhelming majority of Lewis acid sites on zeolites whose sodium ions had been exchanged for di- and tri-valent cations was provided by these latter cations. The quantitative accuracy of the determination of Lewis acid sites was not noticeably affected by the presence of BrOnsted sites on the zeolite.

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ESR measurements of concentration for strong surface acceptor centers on zeolites and Al2O3 using nitroxide radical TEMPON

Cited by 16 publications

References 3 publications

ESR study of nanocrystalline aerogel-prepared magnesium oxide

ESR study of nanocrystalline aerogel-prepared magnesium oxide

EPR and ENDOR studies of carotenoid–solid Lewis acid interactions

Chemisorption of Lewis Bases on Zeolites – A New Interpretation of the Results

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