Spin echo double-resonance

Dipole—dipole (heteronuclear) Af (hetero) Spin-echo double resonance (SEDOR) ... 

A number of other, more sophisdcated, selective averaging tools (includli spin echo, double resonance and two-dimensional techniques) are available, both for spectral editing purposes and for obtaining quantitadve information about inter-... 

We describe in some detail the techniques of nuclear magnetic resonance which are used for studying alumina-supported platinum catalysts. In particular, we describe the spin-echo technique from which the Pt lineshape can be obtained. We also discuss spin echo double resonance between surface Pt and chemisorbed molecules and show how the NMR resonance of the surface Pt can be separately studied. We present examples of experimental data and discuss their interpretation. 

N.M.R. STUDIES of ADSORBED ETHYLENE We have also investigated the reaction of C ethylene with colloidal palladium. Our initial intent was to attempt to observe the formation of ethylidyne from ethylene on the surface of the colloidal palladium particles, a reaction which is known to occur readily on the surface of supported palladium and on palladium single crystals (17). Such a reaction has been identified for ethylene on supported platinum by magnetic resonance experiments in which spin echo double resonance techniques were used to characterize the organic species (18,19), but direct observation of resonances for adsorbed ethylene or ethylidyne was not possible in the highly inhomogeneous solid samples used. The chemical shift differences... 

Abbreviations BCC. body centered cubic DOS. density of states ESR. electron spin resonance HX.AI S, extended X-ray absorption fine structure F CC. face centered cubic (a crystal structure). FID, free induction decay FT, Fourier transform FWHM, full width at half maximum HCP, hexagonal close packed HOMO, highest occupied molecular orbital IR, Infrared or infrared spectroscopy LDOS, local density of states LUMO, lowest unoccupied molecular orbital MAS. magic angle spinning NMR. nuclear magnetic resonance PVP. poly(vinyl pyrrolidone) RF. Radiofrequency RT, room temperature SEDOR, spin echo double resonance Sf, sedor fraction SMSI, strong metal-support interaction TEM. transmission electron microscopy TOSS, total suppression of sidebands. 

The Slichter group (see Section IV.F) uses the following terminology the spin echo double resonance (SEDOR) fraction (Sf) for a pulse... 

The Spin Echo Double Resonance (SEDOR), REDOR and TEDOR experiments are all multiple resonance experiments that exploit heteronuclear dipolar coupling. Qualitative information regarding the proximity of spins I and S, and even quantitative information regarding the I-S distance can be derived. Examples of these approaches applied to materials will be given in later Chapters. Their application to specific areas such as aluminosilicates has been reviewed (Ba et al. 2000). 

Glass formation and local structure in the related system P-Se-Al has also been studied by P and Al NMR which indicates that the local environments of both the P and Al are dominated by the selenium (Hudalla et al. 1998). Although there is evidence of interaction between the Al and P (the formation of four-coordinated P is facilitated by the presence of Al), a more quantitative assessment by Alp P) spin echo double resonance indicates that direct Al-Se-P links occur with less than statistical probability. These results suggest a glass structure which is partially segregated into phosphorus selenide and aluminium selenide-rich regions (Hudalla et al. 1998). 

Static spin echo decay spectroscopy also forms the basis for the measurement of magnetic dipole-dipole interactions between two unlike nuclei I and S. While this interaction is refocused by the Hahn spin echo, it can be recoupled by applying a 7i-pulse to the S-spins during the dipolar evolution period [12]. This manipulation inverts the sign of the heterodipolar Hamiltonian, and thereby interferes with the ability of the Hahn spin echo technique to refocus this interaction. The corresponding pulse sequence, termed SEDOR spin echo double resonance) shown in Fig. 4, compares the I-spin echo intensity as a function of dipolar evolution time (a) in the absence and (b) in the presence of the ti(S) pulses. Experiment (a) produces a decay F(2ti)/Fo, which is dominated by homonuclear dipole-dipole interactions, while experiment (b) results in an accelerated decay, reflecting the contribution from the heteronuclear I-S dipole-dipole interaction, which is now re-introduced into the spin Hamiltonian. For multi-spin systems, a Gaussian decay is expected ... 

H/ Na double resonance NMR techniques have been employed to study the modification of surface hydroxyls on Y-AI2O3 by sodium ions. A H—> Na CP experiment has been used resolve three kinds of sodium cations that are closely associated with surface hydroxyl groups. H Na spin echo double resonance experiments reveal the surface modification in more detail. 

Knight shifts have been measured for Cu and Cu in metallic copper. NMR techniques have been used for the determination of electric field gradients in relation to point defects in metallic copper. Copper-65 NMR and Cu- AJ spin-echo, double-resonance measurements from Cu-exchanged ZSM-5 catalysts have shown the presence of Cu cations. Upon heating, auto-reduction of Cu to Cu was observed, with further reduction to the metal upon exposure to CO at high temperatures. Copper NMR was used to investigate the nanostructure of. ../Cu/CO/Cu... layers which had been prepared by different methods. ... 

Slichter s spin echo approach is a variation on the spin echo double resonance (SEDOR) experiment originally proposed by Hahn I03. To see how this experiment works, consider the spin echo sequences shown in Fig 53. The first case, Fig 53a, describes Hahn s original echo experiment 103. In a hetero-nuclear case (always observing the rare spin) any heteronuclear dipolar interactions (along with the chemical shift and inhomogeneous line broadening processes) will be refocused as a result of this sequence. The second example. Fig 53b, is Hahn s SEDOR experiment (74). Here, the heteronuclear dipole-dipole interaction is not refocused because of the application of the second tt pulse to... 

By spin echo editing NMR method, combined with the H Al spin echo double resonance, a new H signal was found in the thermally treated molecular sieves, reflecting the complexity of hydroxyls as well as the aluminum state in the dehydrated state. It represents an initial stage of the dehydroxylation, or may be related with the initial stage of dealumination. 

Sonochemistry in synthesis Spaciousness index Sphares, silicalite Spheres, mesoporous silica Spheres, MFI, hollow Spheres, zeolite, hollow Spin echo double resonance Spinel ceramic from zeolites Spiropyrane in zeolite Y Sr exchange Sr removal Sr,K-KFl, synthesis SSZ-33 ( CON)... 

The so-called SEDOR technique (spin-echo double resonance [9, 47, 48], see Fig. 5) allows the determination of internuclear distances, rjs, for isolated spin pairs consisting of a resonating J-spin and a non-resonating S-spin. Hahn s echo [49] of the resonating J-spins is observed with a time between the 7i/2-pulse and the 7T-pulse. A rr-pulse applied to the S-spins after a variable time ti (0characteristic damping of Hahn s echo of the resonating /-spins. The damped amplitude, of Hahn s echo under SEDOR conditions is determined by ... 

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