Application of solid state NMR for the study of surface bound species and fossil fuels.

摘要

Recent advances in solid state NMR have been utilized to study a variety of systems. These advancements have allowed for the acquisition of sequences previously only available for solution state detection. The protocol for the measurement of coals and other carbonaceous materials was updated to incorporate the recent advancements in fast magic angle spinning (MAS) and high magnetic fields. Argonne Premium Coals were used to test the sensitivity and resolution of the experiments preformed at high field and fast MAS. The higher field spectra were shown to be slightly less sensitive than the traditional lower field spectra, however, the new high field fast MAS spectra had better resolution. This increased resolution allowed for the separation of a variety of different functional groups, thereby allowing the composition of the coal to be determined. The use of 1 H detection allowed for 2D spectra of coals for the first time. These spectra could be filtered to examine either through-space or through-bond correlations.;Indirect detection via 1 H was also pivotal in the detection of natural abundance 15 N spectra. Through-space and through-bond 2D spectra of natural abundance bulk species are shown with a sensitivity increase of 15 fold over traditional detection. This sensitivity enhancement allowed for the detection of natural abundance 15 N surface bound species in 2D, something that could not be acquired via traditional methods. The increased efficiency of the through-space magnetization transfer, Cross polarization, at fast MAS compared to the slower MAS rates is shown. The through-bond magnetization transfer via INEPT was examined and the effect of J-coupling is confirmed.;Solid State NMR can be utilized to help improve catalytic interactions. Solid state NMR was used to examine the aldol condensation between p-nitrobenzaldehyde and acetone. The formation of a stable intermediate with p-nitrobenzaldehyde was found on the primary functionalized amine mesoporous nanoparticle when the reaction was done in hexane. When secondary amines were used to catalyze the reaction, the reactivity was increased and no intermediate was observed. When the solvent was changed from hexane to water, a dramatic increase in the reactivity of the primary amine was observed. The secondary amine was shown to have a large decrease in activity with the solvent change. The role of surface silanols in the catalysis with the mesoporous silica nanoparticles is also examined.;Implementation of pulsed field gradient fields allowed for an examination of the diffusion of two different solvents, hexane and water, within the primary functionalized amine heterogeneous mesoporous catalyst system. The diffusion of the 2.7 nm pore sizes were compared to the diffusion in the 3.7 nm pores. In hexane the intra-pore diffusion in the smaller pores was slower than the larger pores, agreeing well with the low catalytic yield seen in the aldol reaction.