A comparison of selectivity in catalytic conversion of benzyl alcohol in mesitylene on hybrid lamellar-bulk MFI (HLBM) zeolite materials containing dual meso-/microporosity showed that the external Brønsted acidity in meso-/microporous MFI zeolites effectively impact on selectivity of the parallel alkylation and etherification reactions. HLBM zeolites, consisting of crystalline bulk microporous core and lamellar mesoporous shell, not only catalyzed the parallel reactions on the external environments (external surface and mesopore) but also etherification reaction in the internal environment (micropore) as illustrated by the completely suppressed alkylation and retained residual etherification reactions after 2,6-di-tert-butylpyridine (DTBP) poisoning. A systematic study of HLBM zeolites with tunable meso-/microporous domain sizes achieved by a dual template assisted synthesis revealed that parallel alkylation and etherification reactions are tailored by the tunable external surface area and external acidity of the HLBM zeolites. The external alkylation and etherification reaction rates as a function of cumulative DTBP addition suggested Brønsted acid sites with different strengths on external environments of the HLBM zeolites, which influenced the external etherification reaction, but not as significantly as the alkylation reaction. The evidence shown here for the involvement of external acidity in catalyzing parallel reactions and for the role of external acidity with variable strengths in HLBM zeolite materials extends the scope of observed catalytic behaviors of meso-/microporous zeolite materials beyond those reflecting transport effects and accessibility of acid sites.
The adsorption of 4,4'-bipyridine (BiPy) on Cu(111) has been investigated in 0.1 M HClO4 by cyclic voltammetry, electrochemical scanning tunneling microscopy (STM), and surface-enhanced infrared adsorption spectroscopy (SEIRAS). Cyclic voltammetry showed the double layer region extending from -0.2 to 0.26 V and a pair of redox waves superposing on hydrogen evolution wave at more negative potentials. Diprotonated BiPy, BiPyH2(2+), is adsorbed flat on the Cu(111) (1 x 1) surface and forms a well-ordered monolayer with a (3 x 4) symmetry in the double-layer potential region. At more negative potential, BiPyH2(2+) is reduced to its monocation radical, BiPyH2(*+), and forms another well-ordered structure in which the radicals are stacked in molecular rows with a face-to-face self-dimer as the building unit. The SEIRA spectra of both BiPyH2(2+) and BiPyH2(*+) are dominated by gerade modes which should be IR-inactive for the centrosymmetric species. The breakdown of the selection rule of IR absorption is ascribed to the vibronic coupling associated with charge transfer between BiPyH2(2+) and the surface and between the radicals.
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