Exploring Surface Interactions in Catalysts Using Low-Field Nuclear Magnetic Resonance

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• 作者：Jonathan Mitchell ; Lionel M. Broche ; Thusara C. Chandrasekera ; David J. Lurie ; Lynn F. Gladden
• 刊名：Journal of Physical Chemistry C
• 出版年：2013
• 出版时间：August 29, 2013
• 年：2013
• 卷：117
• 期：34
• 页码：17699-17706
• 全文大小：318K
• 年卷期：v.117,no.34(August 29, 2013)
• ISSN：1932-7455

文摘

Fast field cycling (FFC) nuclear magnetic resonance (NMR) is applied to probe the slow dynamics of liquid molecules imbibed in porous catalysts. The FFC measurements are used to determine surface diffusion correlation and residence times that provide information on the molecular dynamics of surface adsorbed species. The longitudinal relaxation time T₁ dispersion curves reveal biphasic diffusion of adsorbed water that we attribute to the presence of 鈥渟trongly bound鈥?and 鈥渨eakly bound鈥?molecules. FFC measurements of organic liquids (2-butanone, 2-propanol) do not show such behavior. These observations agree with molecular dynamics simulations. The frequency dependence of the relaxation time ratio T₁/T₂ is also considered; it is demonstrated that T₁/T₂ remains a valid indicator of adsorption energy regardless of the field strength at which the measurement is taken in the range B₀ = 0.1 mT to 0.23 T.