Spectroscopic Expression of the External Surface Sites of H-ZSM-5

The nature and spectroscopic expression of external surface sites zeolites, in particular ZSM-5, is a long-debated question. Herein, we use three cutting-edge techniques: Fourier-transform infrared spectroscopy (FTIR) with Fourier self-deconvolution (FSD), high magnetic field proton NMR under fast magic-angle spinning (MAS) periodic boundary Density Functional Theory (DFT) calculations to study models analyze the effect crystallite size. This provides an unequaled description various kinds hydroxyl groups their proximities. hydrogen-bond donor, acceptor or isolated hydroxyls results distinct signals both FTIR spectra, but peak assignment not same from one technique other when chemical changes. Bridging Si–(OH)–Al Al–(H2O) lead overlapping one-dimensional 1H MAS NMR, whereas contributions are strongly different spectra. However, quantification proximity assessment could only be obtained by NMR. With DFT, confirm previous assignments for silanols bridging OH groups. Other (between 3750 3600 cm–1, between 1 4 ppm) assigned extra-framework species (which dedicated models), also enclose signature exposed at ZSM-5. In particular, (?3665 cm–1; 3.8, 2.6 silanol–Al (?3740, 3720, 3665 2.6, 2.2 contribute several features depending on environment. ?1-Al–OH present low amount, 3780 cm–1 signal IR, weak 0–2 ppm interval