fig3

Figure 3. (A) ¹H MAS NMR spectra of HZSM-5 before and after steam treatment; (B) concentrations of different hydroxyl groups by quantifying and fitting the quantitative ¹H MAS NMR spectra; (C) FTIR spectra of the OH vibration region of HZSM-5 before and after steam treatment; (D) ¹H-²⁷Al S-RESPDOR spectra of HZSM-5-300-2 sample with a recoupling time of 0.6 ms. S and S’ denote the ¹H spectrum without and with ²⁷Al irradiation, respectively; ΔS is the difference spectrum obtained by S-S’.