Fig. 1. Structure investigation. (a?c) SEM images of S-1-U1, S-1-U2 and S-1-U3 zeolites and (d?f) iDPC-STEM images of S-1-U1 sample viewed along with different axis.

Fig. 2. Catalytic performance of vapor-phase Beckmann rearrangement. (a) Dependences of CHO conversion on reaction time over various S-1 zeolite catalysts. Reaction condition: 35 wt% CHO and 0.7 wt% H2O in ethanol, 0.3 g of catalyst, WHSV of 6 h?1, and temperature at 380 °C. (b) Dependences of CHO conversion on reaction time over S-1-C and S-1-U1 under conditions of high WHSV. Reaction condition: 35 wt% CHO and 0.7 wt% H2O in ethanol, 0.05 g of catalyst, WHSV of 100 h?1, and temperature at 350 °C. (c) Product selectivity over various S-1 zeolite catalysts at reaction time of 6 h.

Fig. 3. Silanol investigation. (a) 29Si MAS NMR spectra, (b) 1H MAS NMR spectra and (c) FT-IR spectra of the dehydrated S-1 zeolites in OH-stretch region.

Fig. 4. Theoretical simulation. (a) Structural details of three NH3 molecules adsorbed on silanol nest. (b) Averaged NH3 adsorption energy (∆E(NH3)ads) of 1?3 NH3 molecules on four silanols. (c) Representative structure of reactant (R), transition state (TS), and product (P). (d) In the presence or absence of ammonia, geminal silanols, vicinal silanols and terminal silanols react with tetrahydroxysilicon to form the reaction potential energy surface of the Si?O?Si bond.