Probing the Bronsted and Lewis acid sites in zeolite Y with probe molecules and solid-state double resonance NMR

The research presented in this thesis involves a combined use of probe molecules such as trimethylphosphine (TMP) and monomethylamine (MMA), and solid-state double resonance NMR techniques to investigate the interactions between probe molecules and acid sites (i.e., Bronsted and Lewis acid sites) in zeolite Y.; The exact nature of the Lewis acid sites in acidic zeolite catalysts remains unresolved. These sites have been extensively studied with probe molecules and NMR and IR techniques and are thought to be associated with the non-framework alumina clusters formed during the calcination or steaming process used to activated the zeolite. First, {dollar}sp{lcub}31{rcub}{dollar}P/{dollar}sp{lcub}27{rcub}{dollar}Al TRAPDOR NMR has been employed to characterize the Lewis acid sites. The TRAPDOR NMR method allows the aluminum species to be individually studied via their dipolar coupling to the nearly nuclei.; A density-matrix calculation for INEPT experiments involving quadrupolar nuclei in solids has been performed, to understand the evolution behavior of the density matrix under the influence of the quadrupolar interaction, the dipolar and J-couplings, and the pulse lengths applied to the quadrupolar nuclei. The theoretical predictions obtained from these calculations are consistent with the experimental observations of {dollar}sp{lcub}27{rcub}{dollar}Al {dollar}to sp{lcub}31{rcub}{dollar}P INEPT experiments on a TMP-AlCl{dollar}sb3{dollar} complex in zeolite NaX. This method has been employed to determine a {dollar}sp{lcub}31{rcub}{dollar}P-{dollar}sp{lcub}27{rcub}{dollar}Al J-coupling constant of 270 ({dollar}pm{dollar}10 Hz) for TMP bound to the aluminum Lewis acid site in dehydroxylated HY. The coupling constant is consistent with a five-coordinated aluminum Lewis acid/TMP complex, and thus a four-coordinated Lewis acid site.; {dollar}sp{lcub}27{rcub}{dollar}Al/{dollar}sp{lcub}31{rcub}{dollar}P and {dollar}sp{lcub}27{rcub}{dollar}Al/{dollar}sp1{dollar}H REDOR NMR methods have been performed to determine the Al-P and Al-H internuclear distances for a complex formed in HY on adsorption of TMP. An Al-P distance of 3.95 ({dollar}pm{dollar}0.05 A) for this complex is determined. The structure obtained by REDOR NMR is compared with the results of the ab-initio calculations. {dollar}sp1{dollar}H, {dollar}sp{lcub}31{rcub}{dollar}P, and {dollar}sp1{dollar}H/{dollar}sp{lcub}27{rcub}{dollar}Al and {dollar}sp{lcub}31{rcub}{dollar}P/{dollar}sp{lcub}27{rcub}{dollar}Al double resonance MAS NMR has been used to study the Bronsted acidity of CaY, which is activated in an oven (in air) and under vacuum. The {dollar}sp1{dollar}H MAS NMR of CaY, calcined in an oven at 500{dollar}spcirc{dollar}C, shows resonances from H{dollar}sb2{dollar}O (bound to Ca{dollar}sp{lcub}2+{rcub}{dollar} and the zeolite framework), CaOH{dollar}sp+{dollar}, aluminum hydroxides, silanols and Bronsted acid sites ({dollar}approx{dollar}16 Bronsted acid sites per unit cell). No evidence for Lewis acidity is observed. A much lower concentration of Bronsted acid sites ({dollar}<{dollar}1 per unit cell) and no Lewis acidity are observed for CaY calcined under vacuum at 500 or 600{dollar}spcirc{dollar}C. These NMR results have been utilized to understand the very different product distributions for reactions occurring in zeolite CaY as a function of activation conditions.; A combination of variable temperature {dollar}sp1{dollar}H, {dollar}sp{lcub}15{rcub}{dollar}N, and {dollar}sp{lcub}27{rcub}{dollar}Al MAS NMR, and {dollar}sp1{dollar}H/{dollar}sp{lcub}27{rcub}{dollar}Al and {dollar}sp{lcub}15{rcub}{dollar}N/{dollar}sp{lcub}27{rcub}{dollar}Al TRAPDOR NMR has been used to study the adsorption of MMA on dehydrated HY. The adsorption behavior of MMA strongly depends on the loading level, the sample temperature, and the zeolite treatment. These NMR methods enable us to establish that rehydration of HY and then subsequent calcination at 400{dol...