Benzene Adsorbed on Activated Carbon: A Comprehensive Solid-State Nuclear Magnetic Resonance Study of Interactions with the Pore Surface and Molecular Motions

This is the authors' abstract. We don't add key points for this paper.

Benzene- d 6 and cyclohexane- d 12 have been adsorbed on the surface within the pores of high-surface-area activated carbon ( AC ). Their molecular motions have been characterized by variable-temperature 2 H and 13 C solid-state NMR spectroscopy. Three different states of benzene molecules on the AC surface have been found: isotropically moving molecules, bound molecules, and intermediates between these states. In contrast to cyclohexane, benzene assumes stationary states that are stabilized by π–p interactions with the AC surface. Hereby, fast in-plane C 6 rotations take place. The adsorption enthalpy −Δ H 0 for benzene on the surface of AC within the pores was determined as 4.6 ± 0.3 kcal/mol. The strongly adsorbed molecules undergo slow exchange with isotropically moving, liquid-like molecules. In contrast to this, exchange between the molecules in a liquid-like state with benzene in semibound states (T-complexes) is very fast, requiring only low activation energies E act and Δ H ‡ of 3.1 and 2.7 kcal/mol, respectively.