Synergic Effect of Active Sites in Zinc-Modified ZSM-5 Zeolites as Revealed by High-Field Solid-State NMR Spectroscopy

摘要

Understanding the nature of active sites in metal-supported catalysts is of great importance towards establishing their structure-property relationships. The outstanding catalytic performance of metal-supported catalysts is frequently ascribed to the synergic effect of different active sites, which is however not well spectroscopically characterized. Herein, we report the direct detection of surface Zn species and H-1-Zn-67 internuclear interaction between Zn2+ ions and BrOnsted acid sites on Zn-modified ZSM-5 zeolites by high-field solid-state NMR spectroscopy. The observed promotion of C-H bond activation of methane is rationalized by the enhanced BrOnsted acidity generated by synergic effects arising from the spatial proximity/interaction between Zn2+ ions and BrOnsted acidic protons. The concentration of synergic active sites is determined by H-1-Zn-67 double-resonance solid-state NMR spectroscopy.