Solid-state NMR for metal-containing zeolites: from active sites to reaction mechanism

doi:10.1007/s11705-019-1885-1

Front. Chem. Sci. Eng.

2020, Vol. 14

Issue (2) : 159-187 https://doi.org/10.1007/s11705-019-1885-1

REVIEW ARTICLE

Solid-state NMR for metal-containing zeolites: from active sites to reaction mechanism

Xingling Zhao^1,², Jun Xu^1,³(

), Feng Deng¹(

)

¹. National Center for Magnetic Resonance in Wuhan, State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, CAS Key Laboratory of Magnetic Resonance in Biological Systems, Wuhan Institute of Physics and Mathematics, Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, Wuhan 430071, China
². University of Chinese Academy of Sciences, Beijing 100049, China
³. Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074, China

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Abstract

Metal-containing zeolite catalysts have found a wide range of applications in heterogeneous catalysis. To understand the nature of metal active sites and the reaction mechanism over such catalysts is of great importance for the establishment of structure-activity relationship. The advanced solid-state NMR (SSNMR) spectroscopy is robust in the study of zeolites and zeolite-catalyzed reactions. In this review, we summarize recent developments and applications of SSNMR for exploring the structure and property of active sites in metal-containing zeolites. Moreover, detailed information on host-guest interactions in the relevant zeolite catalysis obtained by SSNMR is also discussed. Finally, we highlight the mechanistic understanding of catalytic reactions on metal-containing zeolites based on the observation of key surface species and active intermediates.

Keywords metal-containing zeolites solid-state NMR active site host-guest interaction reaction mechanism

Corresponding Author(s): Jun Xu,Feng Deng

Online First Date: 11 February 2020 Issue Date: 24 March 2020

Cite this article:

Xingling Zhao,Jun Xu,Feng Deng. Solid-state NMR for metal-containing zeolites: from active sites to reaction mechanism[J]. Front. Chem. Sci. Eng., 2020, 14(2): 159-187.

URL:

https://academic.hep.com.cn/fcse/EN/10.1007/s11705-019-1885-1
https://academic.hep.com.cn/fcse/EN/Y2020/V14/I2/159

Fig.1 Brønsted acid sites (BAS) and Lewis acid sites (LAS) on zeolites.

Fig.2 ¹H single-pulse MAS spectrum of (a) HY and ¹H spin-echo MAS spectra of (b) dealuminated HY (without ²⁷Al irradiation), (c) dealuminated HY (with ²⁷Al irradiation), and (d) difference spectra of parts b and c. Reprinted from [⁵] by permission of the American Chemical Society.

Fig.3 ²⁷Al MAS NMR spectra of (a) HY and (b) dealuminated HY. Reprinted from [⁵] by permission of the American Chemical Society.

Fig.4 ²⁷Al spin-echo NMR spectra of (a) non-hydrated zeolites H-Y, (b) deH-Y/7.4, (c) deH-Y/31.1, and (d) deH-Y/81.5. Experimental spectra (top) are compared with simulated spectra (bottom). Reprinted from [⁴⁶] by permission of the American Chemical Society.

Fig.5 ²⁷Al MQMAS NMR spectrum of non-hydrated zeolite deH,Na-Y/81.5 recorded at B₀ = 17.6 T with v_rot = 30 kHz. Reprinted from [⁴⁸] by permission of the Royal Society of Chemistry.

Fig.6 2D ¹H-¹H DQ-MAS NMR spectra of dealuminated HY. Reprinted from [⁵] by permission of the American Chemical Society.

Fig.7 ²⁷Al MAS and DQ-MAS NMR spectra of (a) parent HY, (b) HY-500, (c) HY-600, and (d) HY-700 zeolites. Reprinted from [⁵⁶] by permission of Wiley-VCH.

Fig.8 Experimentally observed spatial proximities of FAL and EFAL species and Brønsted/Lewis acid synergy in dealuminated H-Y zeolites. Reprinted from [³⁹] by permission of the American Chemical Society.

Fig.9 ¹³C CP/MAS NMR spectra of 2-¹³C-acetone adsorbed on HY and dealuminated HY zeolites with different loadings: (a) HY, 2.4 acetone/u.c. (unit cell); (b) dealuminated HY, 1.2 acetone/u.c.; (c) dealuminated HY, 2.4 acetone/u.c.; (d) dealuminated HY, 4.8 acetone/u.c.; (e) dealuminated HY, 7.2 acetone/u.c. Asterisks denote spinning sidebands. Reprinted from [⁵] by permission of the American Chemical Society.

Fig.10 Static ⁹⁵Mo NMR spectra of (a) MoO₃, (b) 10Mo/HZSM-5, (c) 6Mo/HZSM-5, (d) 4Mo/HZSM-5, and (e) 2Mo/HZSM-5. Reprinted from [⁶⁹] by permission of the American Chemical Society.

Fig.11 ⁶⁷Zn MAS NMR spectra of natural abundance pure ZnO powder recorded at 18.8 T by (a) Hahn-echo and (b) HS-QCPMG. Reprinted from [³⁰] by permission of Wiley-VCH.

Fig.12 ⁶⁷Zn HS-QCPMG NMR spectra of (a) ZSM-5(G2), (b) ZSM-5(I2), and (c) ZSM-5(I6). ¹H-⁶⁷Zn S-RESPDOR NMR spectra of ZSM-5(I2) and ZSM-5(I6) with a recoupling time of 9.6 ms (d) and DS/S₀ signal fraction versus the total recoupling time (e). Reprinted from [³⁰] by permission of Wiley-VCH.

Fig.13 ⁷¹Ga QCPMG MAS NMR spectra (a), ¹H-⁷¹Ga S-RESPDOR NMR spectra of Ga/ZSM-5 (redox) with a recoupling time of 12 ms (b), ¹H-⁷¹Ga S-RESPDOR built-up curves of the BAS obtained from Ga/ZSM-5 (redox) fitted by analytical formula (c). Reprinted from [³¹] by permission of the American Chemical Society.

Fig.14 2D ¹H-¹H DQ-MAS NMR spectra of (a) H-ZSM-5, (b) Ga₂O₃/ZSM-5, (c) Ga/ZSM-5(IM), and (d) Ga/ZSM-5(redox). Reprinted from [³¹] by permission of the American Chemical Society.

Fig.15 ¹H MAS NMR spectra recorded at 7.05 T of (a) H-ZSM-5, ZSM-5(G2), ZSM-5(I2), and ZSM-5(I6) and (b) pyridine-d₅ adsorbed on these samples. Reprinted from [³⁰] by permission of Wiley-VCH.

Fig.16 ¹¹⁹Sn NMR spectra of Sn-b after different treatments (top). (a) Calcined; (b) dehydrated after calcination; (c) rehydrated after step (b). ¹¹⁹Sn MAS (d) and CPMAS NMR (e–g) spectra for dehydrated Sn-b (bottom). The cross polarization contact time from ¹H to ¹¹⁹Sn was varied: (e) 0.2 ms; (f) 1.0 ms; (g) 2.0 ms. Reprinted from [¹⁴] by permission of the National Academy of Sciences, USA.

Fig.17 105 K ¹¹⁹Sn DNP-SENS CP magic-angle turning (CPMAT) spectra of 5 wt-% Sn-b (a); spinning sideband manifolds are shown (1–3) for the three different isotropic shifts and the extracted CS tensor parameters are indicated (b). Reprinted from [⁸⁵] by permission of Wiley-VCH.

Fig.18 Span anisotropy versus ¹¹⁹Sn chemical shift for different T sites in Sn-b zeolite: comparison of experimental (black circles) with theoretical data (white diamonds). Reprinted from [⁸⁷] by permission of the American Chemical Society.

Fig.19 ¹H MAS NMR spectra (a–e) and ¹H {¹¹⁹Sn} D-HMQC MAS NMR spectra (f–k) of ¹¹⁹Sn-b with different dehydration and rehydration treatments. Reprinted from [³²] by permission of Springer Nature.

Fig.20 2D ¹H {¹¹⁹Sn} HMQC MAS NMR spectra. (a) Without dehydration; (b) dehydrated at 298 K; (c) dehydrated at 393 K without ¹¹⁹Sn decoupling; (d) dehydrated at 393 K with ¹¹⁹Sn decoupling. Reprinted from [³²] by permission of Springer Nature.

Fig.21 Proposed model for interconversion between open and closed Sn sites in Sn-b zeolite. Reprinted from [³²] by permission of Springer Nature.

Fig.22 ¹³C-{²⁷Al} S-RESPDOR NMR spectra for 2-¹³C-acetone loaded on dealuminated HY zeolite. The blue and red lines represent the spectra observed with (S) and without (S₀) ¹³C-{²⁷Al} S-RESPDOR dipolar dephasing. Reproduced from [⁹²] by permission of the American Chemical Society.

Fig.23 ²⁷Al 3QMAS (a) and ²⁷Al-{¹³C} D-HMQC spectra (b) of 2-¹³C-acetone loaded on dealuminated HY zeolite acquired at 18.8 T under 20 kHz MAS. The asterisk denotes spinning side bands. Reproduced from [⁹²] by permission of the American Chemical Society.

Fig.24 ¹³C MAS NMR spectra of trapped products obtained from reactions of methanol over H-ZSM-5 at 300°C and 350°C for 15 min. The red and black lines represent the spectra observed with and without ¹³C-{²⁷Al} S-RESPDOR dipolar dephasing. Reprinted from [⁹⁶] by permission of Wiley-VCH.

Fig.25 ¹³C MAS NMR spectra of deactivated H-SSZ-13 (a) and HMOR (b) at 400°C for 250 and 100 min, respectively. The black and red lines represent the spectrum observed with (S) and without (S₀) ¹³C-{²⁷Al} S-RESPDOR dipolar dephasing, respectively. The DS/S₀ is indicated in brackets. Reprinted from [⁹⁸] by permission of the American Chemical Society.

Fig.26 ¹³C MAS NMR spectra of trapped products obtained from reaction of ¹³C-methanol over dealuminated H-ZSM-5 zeolite at 250°C for 1 min (a). The black and red lines represent the spectrum observed with (S) and without (S₀) ¹³C-{²⁷Al} S-RESPDOR dipolar dephasing (recoupling time= 1.6 ms). ¹³C-²⁷Al S-RESPDOR built-up data (red dots) of the 52.4 ppm signal and the simulated curves (b). The theoretically optimized local structure of SMS-EFAL complex is displayed in the insert. Reprinted from [¹⁰¹] by permission of Wiley-VCH.

Fig.27 Proposed reaction routes for the formation of C-C bond containing species. Reprinted from [¹⁰¹] by permission of Wiley-VCH.

Fig.28 ¹³C MAS (a, b, d) and ¹³C CP/MAS (c) NMR spectra of ¹³CH₄ activation on ZnZSM-5 at (a) 273 K for 1 h; (b) and (c) 298 K for 1 h; (d) 333 K for 10 min. Reprinted from [⁷⁵] by permission of the Royal Society of Chemistry.

Fig.29 Methane activation and consequent conversion pathway on ZnZSM-5 catalyst (Z donates zeolite support). Reprinted from [⁷⁵] by permission of the Royal Society of Chemistry.

Fig.30 Propane activation mechanism on Ga-containing H-ZSM-5 catalyst. Reprinted from [¹¹⁹] by permission of Elsevier.

Fig.31 Initial products and intermediates resulting from the bifunctional activation of propane on Ga-containing H-ZSM-5 catalysts. Reprinted from [¹²²] by permission of Springer Nature.

Fig.32 ¹³C MAS NMR spectra observed in the course of propane 2-¹³C (a) and propane 1-¹³C (b) reactions over Zn/H-MFI catalyst. Reprinted from [¹¹⁰] by permission of Elsevier.

Fig.33 Initial products and intermediates observed at the initial steps of propane reaction over Zn/HMFI catalyst. Reprinted from [¹¹⁰] by permission of Elsevier.

Fig.34 ¹³C CP/MAS NMR spectra of products formed from co-adsorption of methane and carbon monoxide on Zn/ZSM-5 catalyst heated for 1 h. Reprinted from [¹²⁷] by permission of Wiley-VCH.

Fig.35 Proposed reaction pathways for the formation of acetic acid from methane and carbon monoxide on Zn/ZSM-5 catalyst. Reprinted from [¹²⁷] by permission of Wiley-VCH.

Fig.36 The mechanism of methane activation and reaction over ZnO/H-BEA catalyst. Reprinted from [¹³⁰] by permission of Wiley-VCH.

Fig.37 Proposed ‘‘dual-cycle’’ mechanism in methanol conversion over zeolite. Reprinted from [¹⁴⁰] by permission of Elsevier.

Fig.38 Selectivity of hydrocarbon products (a) and (b), and H₂ production (c) in the MTA reaction over parent H-ZSM-5 and Ga-modified ZSM-5 zeolites with different Ga loadings. Reprinted from [¹⁴⁹] by permission of the American Chemical Society.

Fig.39 ¹³C CP/MAS NMR spectra of trapped species obtained from the MTA reaction on H-ZSM-5 (a) and Ga/ZSM-5 (b–e) zeolites with different Ga loadings. Reprinted from [¹⁴⁹] by permission of the American Chemical Society.

Fig.40 Proposed dehydrogenation and aromatization of cyclopentenes over Ga-modified ZSM-5 zeolite. Reprinted from [¹⁴⁹] by permission of the American Chemical Society.

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