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Interpretation of NMR relaxation as a tool for characterising the adsorption strength of liquids inside porous materials.

D'Agostino C, Mitchell J, Mantle MD, Gladden LF - Chemistry (2014)

Bottom Line: Thus we demonstrate that NMR relaxation measurements have a direct physical interpretation in terms of the characterisation of activation energy of desorption from the surface.Further, for a series of chemically similar solid materials, in this case a range of oxide materials, for which at least two calibration values are obtainable by TPD, the esurf parameter yields a direct estimate of the maximum activation energy of desorption from the surface.The particular motivation for this work is to characterise adsorbate-surface interactions in liquid-phase catalysis.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical Engineering & Biotechnology, University of Cambridge, Pembroke Street, Cambridge CB2 3RA (UK).

No MeSH data available.


T1–T2 correlation plots for water in: a) TiO2-a, b) TiO2-r, c) γ-Al2O3, d) SiO2, e) θ-Al2O3 and f) ZrO2. The solid diagonal line indicates T1=T2; the dashed line indicates T1/T2 at the maximum of the peak. Projected T1,2 distributions are shown for clarity.
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fig03: T1–T2 correlation plots for water in: a) TiO2-a, b) TiO2-r, c) γ-Al2O3, d) SiO2, e) θ-Al2O3 and f) ZrO2. The solid diagonal line indicates T1=T2; the dashed line indicates T1/T2 at the maximum of the peak. Projected T1,2 distributions are shown for clarity.

Mentions: The T1–T2 correlations for water in the porous oxides are shown in Figure 3. In each case, a single relaxation time component is observed; the relaxation times are dominated by surface adsorbed species due to the small pore size and high surface area in these oxides. The ratio T1/T2 is obtained from the logarithmic mean of the individual T1,2 dimensions, which corresponds almost exactly with the maximum intensity of the 2D peak in these mono-modal distributions. In these porous materials with narrow, mono-modal pore size distributions, details of the peak shape are determined predominantly by the raw data quality (degree of smoothing on inversion[43]) and are not considered representative of physical sample properties. The 2D correlations provide a straightforward visual comparison and are required to interpret relaxation results obtained from complicated systems with multiple liquids or diffusive exchange.[24, 29]


Interpretation of NMR relaxation as a tool for characterising the adsorption strength of liquids inside porous materials.

D'Agostino C, Mitchell J, Mantle MD, Gladden LF - Chemistry (2014)

T1–T2 correlation plots for water in: a) TiO2-a, b) TiO2-r, c) γ-Al2O3, d) SiO2, e) θ-Al2O3 and f) ZrO2. The solid diagonal line indicates T1=T2; the dashed line indicates T1/T2 at the maximum of the peak. Projected T1,2 distributions are shown for clarity.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4510707&req=5

fig03: T1–T2 correlation plots for water in: a) TiO2-a, b) TiO2-r, c) γ-Al2O3, d) SiO2, e) θ-Al2O3 and f) ZrO2. The solid diagonal line indicates T1=T2; the dashed line indicates T1/T2 at the maximum of the peak. Projected T1,2 distributions are shown for clarity.
Mentions: The T1–T2 correlations for water in the porous oxides are shown in Figure 3. In each case, a single relaxation time component is observed; the relaxation times are dominated by surface adsorbed species due to the small pore size and high surface area in these oxides. The ratio T1/T2 is obtained from the logarithmic mean of the individual T1,2 dimensions, which corresponds almost exactly with the maximum intensity of the 2D peak in these mono-modal distributions. In these porous materials with narrow, mono-modal pore size distributions, details of the peak shape are determined predominantly by the raw data quality (degree of smoothing on inversion[43]) and are not considered representative of physical sample properties. The 2D correlations provide a straightforward visual comparison and are required to interpret relaxation results obtained from complicated systems with multiple liquids or diffusive exchange.[24, 29]

Bottom Line: Thus we demonstrate that NMR relaxation measurements have a direct physical interpretation in terms of the characterisation of activation energy of desorption from the surface.Further, for a series of chemically similar solid materials, in this case a range of oxide materials, for which at least two calibration values are obtainable by TPD, the esurf parameter yields a direct estimate of the maximum activation energy of desorption from the surface.The particular motivation for this work is to characterise adsorbate-surface interactions in liquid-phase catalysis.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical Engineering & Biotechnology, University of Cambridge, Pembroke Street, Cambridge CB2 3RA (UK).

No MeSH data available.