Oxygen Speciation in Nanophase MgO from Solid-State <sup>17</sup>O NMR

Chadwick, Alan V.; Poplett, I.J.F.; Maitland, David T. S.; Smith, Mark E.

doi:10.1021/cm970629+

Cited by 79 publications

(61 citation statements)

References 32 publications

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“…Hence, a decrease in the copper crystallite size results in a symmetric NMR line broadening, while an increase in strain or disorder causes an asymmetric NMR line profile. [9,24] Figure 12 shows the 63 Cu NMR spectra of the Cu/ZrO 2 catalyst after various reaction steps. Besides differences in the amplitude it can be seen, that the width of the NMR lines varies only slightly as a function of the treatment conditions.…”

Section: Nuclear Magnetic Resonance (Nmr) Spectroscopymentioning

confidence: 99%

In situ investigations of structure–activity relationships of a Cu/ZrO2 catalyst for the steam reforming of methanol

Szizybalski

Girgsdies

Rabis

et al. 2005

Journal of Catalysis

101

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Structure-activity relationships of a nanostructured Cu/ZrO 2 catalyst for the steam reforming of methanol (MSR) were investigated under reaction conditions by in situ X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) combined with on-line mass spectrometry (MS). Temperature programmed activation by reduction in hydrogen or by reduction in a mixture of methanol and water (feed) was studied by time-resolved Cu K edge XANES and TG/DSC/MS measurements. Small and disordered CuO particles were identified as the main copper phase present in the precursors. After extended time on stream and treatment at 673 K in hydrogen, no significant sintering of the copper particles or deactivation of the reduced Cu/ZrO 2 catalysts was detected indicating a superior stability of the material. The initially low steam reforming activity of the Cu/ZrO 2 catalyst after reduction in hydrogen could be significantly increased by a temporary addition of oxygen to the feed. This increased activity after oxidative treatment is correlated to an increasing amount of oxygen in the copper particles.63 Cu NMR studies detected only a minor degree of microstrain in the active copper phase of the Cu/ZrO2 catalyst. The decreased reducibility of CuO/ZrO 2 , the low degree of microstrain, and the correlation between the amount of oxygen remaining in the copper particles and the catalytic activity indicate a different metal support interaction compared to Cu/ZnO catalysts.

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Section: Nuclear Magnetic Resonance (Nmr) Spectroscopymentioning

confidence: 99%

In situ investigations of structure–activity relationships of a Cu/ZrO2 catalyst for the steam reforming of methanol

Szizybalski

Girgsdies

Rabis

et al. 2005

Journal of Catalysis

101

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“…[68,69] Nanocrystalline MgO has been prepared by a variety of routes including sol-gel processing [8-11, 21, 66, 70, 71] and dehydration of the hydroxide. [72] These preparative methods have been followed by a variety of experimental techniques including X-ray crystallography (XRD), 13 C, 17 O and 25 Mg NMR [70] and Mg K-edge XAS [72] and show that careful calcinations are required to fully obtain nanocrystalline MgO. It has been shown that the catalyst used during the hydrolysis and condensation of magnesium methoxide plays a significant role in determining the nature of the material obtained at low calcination temperatures.…”

Section: Introductionmentioning

confidence: 99%

“…It has been shown that the catalyst used during the hydrolysis and condensation of magnesium methoxide plays a significant role in determining the nature of the material obtained at low calcination temperatures. [21] For example, it has been shown that the hydrolysis product of magnesium methoxide is Mg(OH)A C H T U N G T R E N N U N G (OCH 3 ), [70] and that calcination at temperatures greater than 500 8C are required to obtain MgO. [21,70] There is very little EXAFS data concerning MgO [72,73] due to the fact it is a light element.…”

Section: Introductionmentioning

confidence: 99%

“…[21] For example, it has been shown that the hydrolysis product of magnesium methoxide is Mg(OH)A C H T U N G T R E N N U N G (OCH 3 ), [70] and that calcination at temperatures greater than 500 8C are required to obtain MgO. [21,70] There is very little EXAFS data concerning MgO [72,73] due to the fact it is a light element. This results in a lack of data beyond k = 8 and since the resolution available in EXAFS is directly related to the k-range measured, leads to difficulties in resolving the outer shells of the crystal structure.…”

Section: Introductionmentioning

confidence: 99%

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Characterisation of Nanocrystalline Magnesium Oxide by X‐Ray Absorption Spectroscopy

et al. 2007

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There are numerous methods of preparing nanocrystalline materials. Magnesium oxide is an ideal model system on which to probe the relation of the preparative route and the microstructure. Using X-ray absorption spectroscopy (XAS) we show that the sol-gel route can be used to prepare highly crystalline material provided there is careful control of the calcination conditions. In the present work this is achieved by calcining at high temperatures (at least 800 degrees C). However, this results in grain growth that can be prevented by the addition of a pinning agent, SiO(2), during the preparation of the sol. The pinned samples maintain a particle size of 11 nm even after calcining at 1000 degrees C. Ball-milling is a common method of preparing nanocrystalline oxides, however the present work shows that this produces a significant fraction of amorphous material, the fraction increasing with decreasing grain size (e.g. approximately 30 % for a grain size of 23 nm).

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“…[9][10][11]). The main advantage of these methods is their ability to study local properties of the solids that is very important for nanomaterials, namely nanograin ceramics, nanoparticle powders, thin films.…”

Section: Introductionmentioning

confidence: 99%

Size Effects in Radiospectroscopy Spectra of Ferroelectric Nanopowders

et al. 2005

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The theoretical and experimental investigation of ferroelectric nanopowders is performed. The manifestation in radiospectroscopy spectra of size driven ferroelectric-paraelectric phase transition at some critical particle average size R = R c was the main goal of the consideration. In theoretical part the size effect for the materials with ferroelectric tetragonal phase at room temperature and cubic paraelectric phase was considered allowing for the spontaneous polarization inhomogeneity inside a particle and distribution of particle sizes. In ESR the transformation of the spectra from tetragonal symmetry to cubic symmetry lines with decrease in nanoparticle sizes was calculated. The method of Rc value extraction from the ratio of the different symmetry lines intensities in the absorption spectra was proposed. Measurements of Fe 3+ ESR spectra in nanopowder of BaTiO3 were carried out at room temperature. The samples were prepared by rate-controlled method with different particle sizes, which depend on annealing temperature. The decrease in intensity of tetragonal symmetry ESR lines of Fe 3+ and appearance of cubic symmetry line with asymmetry of the shoulders was observed with the average sizes decrease with complete disappearance of tetragonal spectrum at R ≤ 40 nm. The comparison of the theory with experiment was carried out. The theory fits experimental data pretty good. The value of critical size R c ≈ 40 nm was extracted from ESR data. The asymmetry and broadening of right hand side shoulder of ESR cubic symmetry line was shown to be related to contribution of paramagnetic centers in the vicinity of the particles surface with lower than cubic symmetry. The deconvolution of the cubic line allowed to show that this region size is about 3 nm.

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Oxygen Speciation in Nanophase MgO from Solid-State ¹⁷O NMR

Cited by 79 publications

References 32 publications

In situ investigations of structure–activity relationships of a Cu/ZrO2 catalyst for the steam reforming of methanol

In situ investigations of structure–activity relationships of a Cu/ZrO2 catalyst for the steam reforming of methanol

Characterisation of Nanocrystalline Magnesium Oxide by X‐Ray Absorption Spectroscopy

Size Effects in Radiospectroscopy Spectra of Ferroelectric Nanopowders

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Oxygen Speciation in Nanophase MgO from Solid-State 17O NMR

Cited by 79 publications

References 32 publications

In situ investigations of structure–activity relationships of a Cu/ZrO2 catalyst for the steam reforming of methanol

In situ investigations of structure–activity relationships of a Cu/ZrO2 catalyst for the steam reforming of methanol

Characterisation of Nanocrystalline Magnesium Oxide by X‐Ray Absorption Spectroscopy

Size Effects in Radiospectroscopy Spectra of Ferroelectric Nanopowders

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Oxygen Speciation in Nanophase MgO from Solid-State ¹⁷O NMR