Effect of oxygen on the generation of radical ions by synthetic zeolites

Dollish, Francis R.; Hall, W. Keith

doi:10.1021/j100863a037

Cited by 58 publications

(11 citation statements)

References 5 publications

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“…Others (Dollish and Hall, 1967;Neikam, 1967; Stamires and Turkevich, 1964) have reported that as long as 2 days may be required for the radical-ion concentration to reach equilibrium in the type Y zeolites, and although no time-dependency studies were made with H-mordenite, the presence of time-dependent color changes indicated that the radical-ion concentration here too increased with time. Equilibrium was reached sometime within 3 days, however, because no changes in the radical-ion count were observed after longer times.…”

Section: Resultsmentioning

confidence: 99%

“…Effect of the initial degree of benzene saturation upon the desorptive diffusion coefficient; vacuum activation; desorption temp, 25°C; saturation time of 16 hr except as noted at 500°C did not have a significant effect upon the effective diffusion coefficient. Activation in oxygen may cause oxidation of materials on the zeolite as found by Dollish and Hall (1967) or cause small variations in the zeolite structure and/or the positions of residual cations within the structure. The activation procedure clearly affected the chemical interaction of benzene with the zeolite since the color of the saturated H-mordenite was different after oxygen activation, nitrogen activation, or the vacuum activation.…”

Section: Resultsmentioning

confidence: 99%

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Desorption and Counterdiffusion Behavior of Benzene and Cumene in H-Mordenite

Satterfield¹,

Katzer²,

Vieth³

1971

Ind. Eng. Chem. Fund.

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The idealized mordenite pore structure comprises an array of parallel tubes only slightly greater in diameter than the minimum effective diameter of benzene and cumene molecules, and they cannot readily counterdiffuse in mordenite. The cumene desorptive diffusion coefficient from H-mordenite into benzene at 25°C decreased by over two orders of magnitude as the time of saturation before desorption was increased to 6 days. This decrease seems to be caused by the slow formation in the H-mordenite pores during the saturation step of radical ions and diisopropylbenzene molecules, the latter by the disproportionation of cumene. Both of these cause blockage of the pores. Most of the surface area of H-mordenite is apparently unavailable for reaction of aromatic species at temperatures moderately above ambient.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Desorption and Counterdiffusion Behavior of Benzene and Cumene in H-Mordenite

Satterfield¹,

Katzer²,

Vieth³

1971

Ind. Eng. Chem. Fund.

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“…A similar phenomenon is responsible for the single electron transfer which occurs when polynuclear aromatic hydrocarbons form radical ions on the surfaces of aluminum-silicates; the electron acceptor in these cases is 02. 32 The transfer of an electron from perylene to O2 does not take place in inert solvents or on the surface of silica gel. It does take place on the surface of decationated zeolites after they have become dehydr~xylated.~~ It also occurs on the surfaces of zeolites which contain multivalent base-exchange cations and Richardson 31 has shown that the extent of the reaction varies exponentially with the electron affinity of the cation.…”

Section: Discussionmentioning

confidence: 99%

Studies of the hydrogen held by solids. Part 15.—Cation exchanged zeolites

Christner¹,

Liengme²,

Hall³

1968

Trans. Faraday Soc.

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Dehydration of multivalent ion-exchanged zeolites produced structural hydroxyl groups of varying thermal stability as evidenced by differences in the retention of their L-r. bands on heating in uacuo. The retention increased with the electron af6nity of the base-exchange cation. Although the i.-r. bands in the 3650 and 3545 cm-l regions appeared to have the same chemical identity as those formed by heating the NHZ-zeolite, these hydroxyl groups were less reactive with pyridine (Py). Temperatures of 85-150" were required to react a substantial fraction of them to PyH+, whereas with the decationated zeolites, both bands were removed by Py interaction at room temperature although the 3545 cm-' band could be restored to its original intensity by evacuation at 150".Py also co-ordinated with the base-exchange cations (became Lewis bonded). The strength of this interaction (retention of PyL at elevated temperatures) increased with the electron affinity of the cation and the frequency of the corresponding i.-r. band increased concomitantly from 1443 cm-' (Na+) to 1455 cm-l (Zn2+). Addition of H20, or H20+C02, effected conversion of PyL to PyH+, and again the extent of these reactions paralleled the electron affinity of the cation.

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“…The same principle can be extended to zeolite which is a class of three-dimensionally interconnected inorganic polymers consisting of silicon, aluminum, and oxygen atoms, along with the exchangeable charge-balancing cations, which exist within the voids created by the negatively charged framework. It is therefore reasonable to expect that either the framework or the countercation, individually or in combination, would exert a donor − or an acceptor − property toward the incorporated guest molecules depending on their relative electron richness …”

Section: Introductionmentioning

confidence: 99%

Iodine as a Visible Probe for the Evaluation of Zeolite Donor Strength

et al. 1996

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The visible absorption band of iodine adsorbed on zeolite blue-shifted with increasing the electropositivity of the countercation and the aluminum content in the framework. This phenomenon was attributed to the increase in the donor strength of the zeolite framework based on the analogous spectral shift of iodine in solution. In support of this, a negative linear correlation was observed between the measured visible bands of iodine adsorbed on various zeolites and their calculated Sanderson's intermediate electronegativities. However, the simultaneous change in the electrostatic field strength within the zeolite pores, as a result of the change in the number and the size of the cation, has to be taken into account in order to interpret the overall spectral shifts more precisely. The iodine band sensitively blue-shifted with decreasing the moisture content in the framework but red-shifted with the loss of NH3 from NH4 +-exchanged zeolites. The visible band of iodine also progressively red-shifted with increasing the adsorbed amount, presumably due to the nature of iodine to deplete electron density from the framework. The framework structure also affected the spectral shift of the visible iodine band. The overall results established that iodine can be used as a novel molecular probe for the quantitative evaluation of the zeolite donor strength.

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Effect of oxygen on the generation of radical ions by synthetic zeolites

Cited by 58 publications

References 5 publications

Desorption and Counterdiffusion Behavior of Benzene and Cumene in H-Mordenite

Desorption and Counterdiffusion Behavior of Benzene and Cumene in H-Mordenite

Studies of the hydrogen held by solids. Part 15.—Cation exchanged zeolites

Iodine as a Visible Probe for the Evaluation of Zeolite Donor Strength

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