State 27Al Nuclear Magnetic Resonance Research Articles

Regioselective nitration of toluene to para‐nitrotoluene with NO2 over dealumination Hβ zeolite: Comparison of organic and inorganic acids

AbstractThis work presents a novel heterogeneous catalytic system for the preparation of para‐nitrotoluene (p‐NT) with nitrogen dioxide (NO2) as a nitrating agent in the presence of oxygen (O2). By applying dealuminated Hβ zeolite treated with oxalic acid (Hβ‐Ox) as a catalyst, p‐NT can be obtained with high conversion (90.5%) and selectivity (72.6%). In addition, it can be recycled at least five times without a significant decrease in catalytic activity. This result demonstrates that the catalyst has high efficiency, good stability, and regenerability. Meanwhile, the characteristics of pristine Hβ and different dealuminated Hβ zeolites modified with organic and inorganic acids were systematic contrastive studied using X‐ray diffraction (XRD), nitrogen (N2) adsorption‐desorption, Fourier‐transform infrared (FT‐IR), scanning electron microscope (SEM), temperature‐programed desorption of ammonia (NH3‐TPD), pyridine adsorption infrared (Py‐FT‐IR), and solid state 27Al nuclear magnetic resonance (27Al MAS‐NMR). Finally, the higher conversion and para‐selectivity over Hβ‐Ox also give a reasonable explanation in this paper.

Deactivation of Cu-SSZ-13 in the presence of SO2 during hydrothermal aging

Cu2+-exchanged zeolite catalysts with the chabazite (CHA) structure have been thought to be optimal candidates for selective catalytic reduction of NOx with NH3. In real applications, however, SCR catalysts readily undergo hydrothermal aging and sulfur poisoning. In this work, the co-effect of SO2 and hydrothermal aging at high temperature was investigated. Different from the reversible inhibition of SO2 poisoning that occurs at low temperatures, the sulfur poisoning at high temperature is permanent due to the destruction of the zeolite structure, and no deposit of sulfate is observed. Cu-SSZ-13 catalysts were characterized through solid state 27Al nuclear magnetic resonance (27Al-NMR), X-ray diffraction (XRD), temperature-programmed desorption of NH3 and NO (NH3/NO-TPD), electron paramagnetic resonance (EPR), temperature-programmed reduction by H2(H2-TPR), in situ DRIFTS, and thermogravimetric analysis with mass spectrometric detection (TG-Mass) to develop an understanding of the degradation mechanisms during hydrothermal aging and sulfurization at high temperature. The results indicated that SO2 dislodged the extra-framework Al atoms that resulted from the dealumination process that occurs during hydrothermal aging. More Cu2+ species were accumulated as CuOx for Cu-SSZ-13 after sulfurization at high temperature compared to that treated by hydrothermal aging only. The dealumination and accumulation of Cu2+ species caused a loss of acid and active sites for the Cu-SSZ-13 catalyst, and resulted in degradation of NH3-SCR performance.

Modification and sequential treatment of EU-1 zeolite in mild alkali and alkaline-acid conditions

EU-1 zeolites were sequentially treated with low-concentration sodium carbonate (Na2CO3) and hydrochloric acid (HCl) solutions. The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), N2 adsorption/desorption, temperature programmed desorption of NH3 (NH3-TPD), solid state 27Al nuclear magnetic resonance (27Al NMR), and the catalytic performances of the treated samples were tested in the xylene isomerization reaction. The results showed that the external surface area and mesoporous volume of the sample sequentially treated with 0.05mol·L−1 Na2CO3 and 0.1mol·L−1 HCl solutions reached 73.9m2·g−1 and 0.162cm3·g−1, respectively. The catalytic performances of EU-1 zeolites were significantly improved, that the activity of the probe reaction increased from 23.03% to 23.61% and the selectivity increased from 85.09% to 87.14% compared with those of parent sample. Furthermore, it was found that only amorphous silica and alumina species was dissolved during the post-treatment process, but the framework structure and the acidic properties of EU-1 zeolite remained intact.

Solid state 27Al NMR and X-ray diffraction study of alumina–carbon composites

The structural and chemical transformations occurring in alumina–carbon composites upon heat treatment were investigated by using a combination of X-ray diffraction (XRD) and solid-state 27Al nuclear magnetic resonance (NMR) spectroscopy. Two different carbon precursors were employed: a commercial activated carbon and a char obtained by carbonization of the endocarp of babassu coconut at 700°C. The alumina–carbon composites were prepared by aqueous impregnation of the carbon supports with aluminum nitrate and, after filtering and drying, the as-synthesized powders were heat-treated under argon flow at temperatures up to 1000°C. The Al compounds present in the as-synthesized samples were identified by XRD and solid-state 27Al NMR as nanocrystalline aluminum oxyhydroxides or hydroxides, depending on the synthesis conditions. All Al-containing phases were XRD-amorphous in the char-derived nanocomposites, with the presence of a distribution of AlO6 (octahedral Al site), AlO5 (pentacoordinated Al) and AlO4 (tetrahedral Al site) units revealed by solid-state 27Al NMR spectroscopy. The heat treatments caused the formation of transition aluminas dispersed over the carbon supports, with the occurrence of different amounts of AlO6, AlO5 and AlO4 units depending on the heat treatment temperature and on the type of carbon precursor used for the preparation of the composites.

Synthesis and characterization of Al- and In-doped CdSe nanocrystals

Al- and In-doped CdSe nanocrystals were synthesized using a three-part core-shell synthesis. CdSe core nanocrystals were first prepared, then allowed to react with dopant precursors in the presence of weakly binding ligands, and finally overcoated with an additional shell of CdSe. The addition of Al dopants quickened shell overgrowth and led to more monodisperse nanocrystals while the addition of In dopants produced more polydisperse particles, as seen by absorption spectroscopy. Elemental analysis combined with chemical etching revealed the dopants were inside the particles and solid state 27Al nuclear magnetic resonance (NMR) spectra indicated that the Al impurities were well dispersed. When the Al-doped nanocrystals were processed into thin-film transistors, enhanced n-type transport was observed with a rise in the Fermi level compared to undoped particles.

Aluminum binding to phosphatidylcholine lipid bilayer membranes: 27Al and 31P NMR spectroscopic studies

27Al and 31P nuclear magnetic resonance (NMR) spectroscopies were used to investigate aluminum interactions at pH 3.4 with model membranes composed of 1-palmitoyl-2-oleoyl- sn-glycero-3-phosphocholine (POPC). A solution state 27Al NMR difference assay was developed to quantify aluminum binding to POPC multilamellar vesicles (MLVs). Corresponding one-dimensional (1D) fast magic angle spinning (MAS) 31P NMR spectra showed that aluminum induced the appearance of two new isotropic resonances for POPC shifted to −6.4 ppm and −9.6 ppm upfield relative to, and in slow exchange with, the control resonance at −0.6 ppm. Correlation of the 27Al and 31P NMR binding data revealed a 1:2 aluminum:phospholipid stoichiometry in the aluminum-bound complex at −9.6 ppm and a 1:1 aluminum:phospholipid stoichiometry in that at −6.4 ppm. Slow MAS 31P NMR spectra demonstrated shifts in the anisotropic chemical shift tensor components of the aluminum-bound POPC consistent with a close coordination of aluminum with phosphorus. A model of the aluminum- bis-phospholipid complex is proposed on the basis of these findings.

Solid-state 27Al Nuclear Magnetic Resonance Investigation of Plasma-facilitated NOx Reduction Catalysts

Aluminum coordination distribution for alumina catalysts supported on mesoporous silica was examined. It was shown that aluminum coordination correlates to activity of the catalysts for plasma-enhanced, selective catalytic reduction of NOx with propene. Catalysts were prepared by incorporating aluminum onto the surface of a mesoporous silica support via three different post-synthesis routes to produce varying aluminum coordination. Aluminum trichloride, sodium aluminate, and aluminum isopropoxide precursors were examined. High-resolution, solid state 27Al nuclear magnetic resonance was used to determine aluminum coordination distributions for the resulting catalysts. Unsaturated aluminum sites (i.e., structural defects) correlated with increased activity at high temperatures while tetrahedrally-coordinated aluminum or BrØnsted acid sites correlated with activity at low temperatures.

Solid state 27Al NMR and FTIR study of lanthanum aluminosilicate glasses

The structure of lanthanum aluminosilicate (LAS) glasses, containing: (15–25) mol% La2O3, (15–35) mol% Al2O3 and (40–70) mol% SiO2, were studied by 27Al nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR). The effects of La2O3 and Al2O3 content on the properties and structure of the LAS glasses were evaluated. Al3+ ion enters into the glass structure mainly in fourfold co-ordination, forming (AlO4/2)− tetrahedra, and only in small amounts in fivefold and sixfold co-ordination. La3+ acts as network modifier, producing more non-bridging oxygen atoms as its content increases.

Synthesis and characterization of aluminum propionate sol-gel derived Al 2O 3

Al 2O 3 has been synthesized from aluminum propionate [Al(CO 2CH 2CH 3) 3] by Sol-Gel techniques. Methods of characterization include: x-ray powder diffraction, scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR). Solution and solid state 13C and 27Al NMR data is coupled with both x-ray diffraction powder data and SEM in order to understand the transition from sol → gel → amorphous powder → crystalline powder in the sonicated and unsonicated aluminum propionate precursor, and Al 2O 3 powders. Results indicate that the sonicated dried powder is crystalline, having the γAl 2O 3 structure while the unsonicated dried powder is amorphous and crystallizes at 800°C with the α Al 2O 3 structure. These differences in crystallinity are further substantiated by solid state 27Al NMR chemical shifts and line widths at half height.

Synthesis and Characterization of Aluminum Propionate Sol-Gel Derived Al2O 3

ABSTRACTAl2O3 has been synthesized from aluminum propionate [A1(CO2CH2CH3)3] bySol-Gel techniques. Methods of characterization include: x-ray powder diffraction, scanning electron microscopy (SEM) and nuclear magnetic resonance(NMR). Solution and solid state 13C and 27Al NMR data is coupled with bothx-ray diffraction powder data and SEM in order to understand the transitionfrom sol + gel + amorphous powder + crystalline powder In the sonicated andunsonicated aluminum propionate precursor, and A12O3 powders. Resultsindicate that the sonicated dried powder is crystalline, having the γA12O3structure while the unsonicated dried powder is amorphous and crystallizesat 800°C with the a A12O3 structure. These differences in crystallinity arefurther substantiated by solid state 27AL NMR chemical shifts and linewidths at half height.