Characterization of Local and Non-local Interactions of Stoichiometric Adsorption Complexes in High-Silica Zeolite

教授们。戈特和怀特将研究化学吸附分子与高硅沸石(如ZSM-5)中的Bronsted酸位的相互作用。他们将确定反应中间体，确定1：1化学计量比络合物的形成能量及其远程相互作用，并通过分子动力学对表面化学进行建模。他们将检查来自工业上重要的反应物分子的吸附中间体，如醇、硫醇、醛、酯、酚和取代芳烃，并将识别适合于表征远程相互作用的分子探针。用TPD、TGA、多相固体核磁共振、NQR和IR对其进行了光谱表征。在核磁共振工作中，沸石将以大单晶的形式安装在毛细管中，并具有随机取向。核磁共振波谱将涉及多相脉冲序列、线变窄序列、魔角旋转和同位素替代，以及REDOR和PISMA等技术。特别重要的是添加了甲基的H-核磁共振来研究酸中心的环境。具有不同官能团的弱碱性分子的微量热学信息将与光谱相关联，目的是使表面反应的能垒合理化。这些结果将得到结构和能量的从头算量子化学计算，以及分子筛团簇模型中探针分子的化学吸附和反应步骤的从头算量子分子动力学的补充。

Profs. Gorte and White will investigate the interaction of chemisorbed molecules with Bronsted acid sites in high-silica zeolites, such as ZSM-5. They will identify the reaction intermediates, determine the energetics of formation of 1:1 stoichiometric complexes and their long-range interactions, and model the surface chemistry by molecular dynamics. They will examine adsorbed intermediates derived from industrially significant reactant molecules, such as alcohols, thiols, aldehydes, esters, phenols and substituted aromatics, and will identify molecular probes suitable for the characterization of long-range interactions. The spectroscopic characterization will be done with TPD, TGA, multi-phase solid-state NMR, NQR, and IR. For the NMR work, the zeolite will be in the form of large single crystals mounted with random orientations in capillary tubes. The NMR spectroscopy will involve multiphase-pulse sequences, line-narrowing sequences, magic-angle spinning and isotopic substitution, with techniques such as REDOR and PISMA. Particularly important is the addition of H NMR of methyl groups to investigate the environment of the acid sites. Information from microcalorimetry of weakly basic molecules having various functional groups will be correlated with the spectroscopy, with the objective of rationalizing the energy barriers for surface reactions. Those results will be complemented with ab initio quantum chemistry calculations of structures and energies, and ab initio quantum molecular dynamics of the chemisorption and reaction steps of probe molecules in cluster models of the zeolites.