Adsorption and Desorption Behavior of NO on H-ZSM-5, Na-ZSM-5, and Na-A as Studied by EPR

Rudolf, Thomas; Böhlmann, Winfried; Pöppl, Andreas

doi:10.1006/jmre.2002.2504

Cited by 19 publications

(20 citation statements)

References 30 publications

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“…Spectra of all samples show at temperatures T ≤ 62 K a signal which is typical for a paramagnetic species with electron spin S = 1/2 and a nearly axially symmetric g-tensor with principle values g xx,yy ≈ 1.95 ± 0.4 > g zz (S7, S8). We attribute it to NO molecules adsorbed at diamagnetic sites [23][24][25][26][27] . Unfortunately the g zz powder edge singularity, which is most sensitive to the electric field at the adsorption site, is not resolved.…”

Section: Resultsmentioning

confidence: 96%

“…25 The electronic ground state of NO becomes paramagnetic leading to a characteristic EPR signal of an electron spin S = 1/2 at g-values near but smaller than the free electron one g e = 2.0023. 23,[25][26][27] In case of the MOF DUT-8(Ni) another interesting aspect might be the possibility of NO molecules to form paramagnetic complexes with the Ni 2+ ions. 28 mmol) were dissolved in 21 ml DMF.…”

Section: Introductionmentioning

confidence: 99%

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EPR Insights into Switchable and Rigid Derivatives of the Metal–Organic Framework DUT-8(Ni) by NO Adsorption

et al. 2016

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The metal-organic framework (MOF) DUT-8(Ni) (DUT = Dresden University of Technology) shows a structural transformation from a non-porous to a porous phase during the adsorption of gases. A rigid derivative of this material has recently been synthesized, where this "gate pressure like" flexibility is completely absent. This rigid derivative of DUT-8(Ni) always stays in the porous phase even in the absence of any adsorbate. This motivates the present investigation of the adsorption of nitric oxide (NO) on the flexible and rigid forms of DUT-8(Ni) by continuous wave electron paramagnetic resonance (EPR) spectroscopy at Xband frequency. The EPR signal of desorbed NO is measured at moderate temperatures and the decrease of its intensity indicates the adsorption of this gas within the porous phase of DUT-8(Ni) at low temperatures. An adsorption and desorption related hysteresis loop of the intensity of this signal is observed for the flexible but not for the rigid . This difference might reflect the difference in the flexibility of both materials. Furthermore EPR signals with electron spin S = 1/2 are measured, which can likely be attributed to Ni 2+ -NO adsorption complexes at defective paddle wheel units within the porous phase of with the unpaired electron sitting at the Ni 2+ ion. The order of their g-tensor principle values allows a distinct characterisation of the ligand environment of these ions. Defects for which the EPR signals indicate, that at least one NDC (2,6-naphthalenedicarboxylate) ligand molecule does not coordinate to the paddle wheel, are only observed for the rigid but not for the flexible . Also the density of defective paddle wheel units with only one Ni 2+ ion or a missing dabco (1,4 -diazabicyclo[2.2.2]octane) ligand is indicated to be one order of magnitude larger in the rigid than in the flexible derivative of this MOF. The observed differences in the presence and amount of distinct defects might be related to the difference in the flexibility of both forms of the investigated material.

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Section: Resultsmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

EPR Insights into Switchable and Rigid Derivatives of the Metal–Organic Framework DUT-8(Ni) by NO Adsorption

et al. 2016

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“…As it has been pointed out by other authors [8,13], the line width of the EPR signal of NO gas might also be used to determine the amount of desorbed NO. Indeed it has been reported for other paramagnetic gases like molecular oxygen [14,15] or fluorine [16], that the line width of their EPR signals is linearly related to the corresponding gas pressures.…”

Section: Introductionmentioning

confidence: 97%

“…Since EPR is quite sensitive to small amounts of NO gas, this method is well suited to determine the characteristic temperature, where desorption of NO from the host material starts. To determine the total amount of desorbed NO, one has to compare such results with EPR signals of samples with a known amount of pure NO gas as it has been done by Rudolf et al [12,13]. This step is necessary since one has to deal with the temperature dependence of the paramagnetic susceptibility of the corresponding rotational state which follows a Curie law and its temperature-dependent population.…”

Section: Introductionmentioning

confidence: 98%

“…The signal intensity depends on the paramagnetic susceptibility and the population of the corresponding rotational state responsible for the EPR signal [12] as well as the total number of NO molecules inside the microwave cavity. Its measurement has been already used to study the desorption of NO from zeolites [12,13]. Since EPR is quite sensitive to small amounts of NO gas, this method is well suited to determine the characteristic temperature, where desorption of NO from the host material starts.…”

Section: Introductionmentioning

confidence: 98%

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The Line Width of the EPR Signal of Gaseous Nitric Oxide as Determined by Pressure and Temperature-Dependent X-band Continuous Wave Measurements

Mendt

Pöppl

2015

Appl Magn Reson

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The electron paramagnetic resonance (EPR) signal of gaseous nitric oxide (NO) has been measured by continuous wave X-band experiments at room temperature at gas pressures between 1 mbar and 60 mbar and at a gas pressure of 48 mbar at different low temperatures. A phenomenological spin Hamiltonian approach allows simulating each EPR signal of NO by changing only a single line width parameter. At room temperature, this line width depends linearly on the NO gas pressure which can be explained by kinetic gas theory. An effective collisional cross section has been determined by this way which is about twice as large as the known cross section for NO derived from viscosity measurements. Experiments with NO gas at low temperatures are consistent to the line width interpretation by kinetic theory. In total, the results demonstrate that in NO adsorption and desorption experiments at different temperatures and NO gas pressures below 60 mbar the amount of desorbed NO can simply be determined in situ by the line width of this signal, which one can obtain easily from a conventional simulation procedure.

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Continuous Wave EPR of Radicals in Solids

Lund¹,

Liu²

2003

EPR of Free Radicals in Solids

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Adsorption and Desorption Behavior of NO on H-ZSM-5, Na-ZSM-5, and Na-A as Studied by EPR

Cited by 19 publications

References 30 publications

EPR Insights into Switchable and Rigid Derivatives of the Metal–Organic Framework DUT-8(Ni) by NO Adsorption

EPR Insights into Switchable and Rigid Derivatives of the Metal–Organic Framework DUT-8(Ni) by NO Adsorption

The Line Width of the EPR Signal of Gaseous Nitric Oxide as Determined by Pressure and Temperature-Dependent X-band Continuous Wave Measurements

Continuous Wave EPR of Radicals in Solids

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