Solid-state Nuclear Magnetic Resonance Spectrometry Research Articles

Functionalization of mesoporous Al-MCM-41 for indoor humidity control as building humidity conditioning material

This study sought to overcome the high energy consumption of mechanical dehumidifiers by synthesizing humidity control materials using alumino-silicate raw materials extracted from stone sludge and cathode ray tube (CRT) waste panel glass. The structure of the synthesized materials matches that of Mobil Composition of Matter No. 41 (MCM-41) mesoporous molecular sieves, which was subjected to amine functionalization using (3-Aminopropyl) triethoxysilane at various concentrations (2.5, 5, 7.5 vol.%). The resulting materials were characterized using X-ray fluorescence analysis, small angle X-ray diffractometry, Fourier transform infrared spectroscopy, transmission electron microscopy, the Brunauer–Emmett–Teller method, and 27Al solid-state nuclear magnetic resonance spectrometry. Al-MCM-41 molecular sieves with 5.0% grafted amine functional groups presented high specific surface area and high pore uniformity resulting in the highest equilibrium moisture content (39.4 kg/kg). The high thermal and humidity buffer capacity of the proposed material could greatly enhance the comfort of interior spaces without the energy consumption of mechanical dehumidifiers.

Studies of physicochemical and chromatographic properties of mixed amino-alkylamide bonded phases

Mixed amino-alkylamide chemically bonded phases have been prepared via two-step reaction which involved the initial modification of silica with aminopropyldimethylsilyl groups under environmentally sealed conditions followed by a secondary derivatization with different acid chlorides ( i.e., acetyl, hexanoyl and stearoyl chlorides). In addition, for comparative purposes two conventional C 18 phases with different coverage densities have been prepared. Subsequently, the physical properties of the mixed phases have been studied by liquid chromatography as well as by elemental analysis and solid-state nuclear magnetic resonance spectrometry. The resulting data have provided information about how the hydrophobic chains and the specific interaction sites in the bonded phases influence solute retention under reversed-phase conditions. A potentially important application of the mixed amino-alkylamide materials is for separating basic compounds such as amines and amides.

Reactions of butadiene in zeolite catalysts by in situ variable-temperature solid-state nuclear magnetic resonance spectrometry

The mechanisms by which butadiene oligomerizes in acidic zeolite catalysts leading to deactivation by pore blockage have been elucidated by using in situ {sup 13}C solid-state NMR spectroscopy with magic-angle spinning (MAS). Butadiene is found to oligomerize primarily by the 1,4-addition reaction upon adsorption at its melting point (164 K). Secondary reactions of the oligomers are strongly dependent upon the properties of the zeolite. The initially formed linear product undergoes cyclization reactions to form fused rings in zeolite HY, but isolated rings are formed in the smaller channels of zeolite HZSM-5. Branching reactions and/or 1,2 enchainment result in an appreciable methyl group content in the oligomers formed in zeolite HY. These results provide insight into the mechanisms by which oxide catalysts are deactivated by pore blockage. Neither carbenium ions nor any other reactive intermediates were observed spectroscopically, presumably because such intermediates reacted with either free butadiene or the oligomers so rapidly as to preclude a detectable steady state concentration.

Structural analysis of geochemical samples by solid-state nuclear magnetic resonance spectrometry. Role of paramagnetic material

An examination of coals, coal tars, a fulvic acid, and soil fractions by solid-state /sup 13/C NMR spectrometry has demonstrated widely differing behavior regarding quantitative representation in the spectrum. Spin counting experiments on coal tars and the fulvic acid show that almost all the sample carbon is observed in both solution and solid-state NMR spectra. Similar experiments on two coals (a lignite and a bituminous coal) show that most (70-97%) of the carbon is observed; however, when the lignite is ion exchanged with 3% (w/w) Fe/sup 2 +/, the fraction of carbon observed drops to below 10%. In additional experiments signal intensity from soil samples is enhanced by a simple dithionite treatment. This is illustrated by /sup 13/C, /sup 27/Al, and /sup 29/Si solid-state NMR experiments on soil fractions.