Silica-confined Cu2O nanoparticles for propylene epoxidation with molecular oxygen

doi:10.1016/S1872-2067(26)65059-0

Abstract

Abstract:

The direct propylene epoxidation with molecular oxygen offers an atom-economical route to propylene oxide (PO). However, the oxidative reaction conditions required at high temperatures often induce complete propylene oxidation and the reconstruction of the active centers, compromising PO selectivity. Herein, we propose a redispersion-confinement strategy to encapsulate small, low-valence Cu nanoparticles (NPs) within a silica shell, thereby achieving stable dispersion across various supports. We confirm that the formation of Cu-O-Si coordination between Cu and silica, together with cesium promotion, could stabilize the small Cu NPs and enhance the PO formation. The optimum Cs-Cu@Si/SBA-15 catalyst delivers a 3.9% propylene conversion and a 68% PO selectivity, markedly surpassing the 0.6% conversion and 42% selectivity obtained over Cs-Cu/SBA-15 without the silica shell. A significant space and chemical state confinement effect is evidenced between CuO and the silica shell, which retards the reactivity of lattice oxygen and allows the moderate activation of molecular oxygen to electrophilic oxygen species; thus, promoting the selective epoxidation of propylene. This strategy offers a general approach for molecular-level control of active-site structure and electronic states in heterogeneous catalysts.

Key words: Copper catalyst, Confinement, Surface engineering, Propylene epoxidation, Oxidation-reduction reactions

Jiawei Cheng, Kai Wang, Yuhan Meng, Jiachen Wang, Zuozheng Liu, Jingjuan Wang, Jiaxu Liu, Kang Cheng, Qinghong Zhang, Ye Wang. Silica-confined Cu₂O nanoparticles for propylene epoxidation with molecular oxygen[J]. Chinese Journal of Catalysis, 2026, 86: 77-88.

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URL: https://www.cjcatal.com/EN/10.1016/S1872-2067(26)65059-0

https://www.cjcatal.com/EN/Y2026/V86/I7/77

Figures/Tables 9

Fig. 1. (a) Schematic illustration of the synthesis procedure for the Cu@Si catalyst series. (b) C3H6 epoxidation performance of Cu-based catalysts and Cu@Si catalysts on different carriers under Cs-assisted conditions. (c) The activity of Cs-Cu@Si/SBA-15 varies with reaction time. (d) The comparison between the activity of typical Cu-based catalysts in the literature and the catalyst in this work. Reaction condition: Wcat = 0.1 g, C3H6/O2 = 1/39 (molar ratio), Ftotal = 60 mL·min-1, T = 250 °C, P = 1 bar, time on stream = 30 min. Detailed catalytic performance can be found in Tables S2-S4.

Fig. 2. The effect of the temperature on the epoxidation performance of Cs-Cu/SBA-15 (a) and Cs-Cu@Si/SBA-15 (b). The apparent activation energy of Cs-Cu@Si/SBA-15 and Cs-Cu/SBA-15 based on the propylene conversion (c) and PO formation (d). Reaction conditions: Wcat = 0.1 g, C3H6/O2 = 1/39 (mol ratio), Ftotal = 60 mL·min-1, T = 200-300 °C, P = 1 bar, time on stream = 30 min.

Fig. 3. (a) XRD patterns. (b) UV-Vis DRS of Cu/SBA-15, Cu@Si/SBA-15, and Cs-Cu@Si/SBA-15. (c) N2 adsorption-desorption isotherms and pore size distribution of SBA-15, Cu/SBA-15, and Cs-Cu@Si/SBA-15.

Fig. 4. The AC-HAADF-STEM image and elemental mapping of Cu@Si/α-Al2O3.

Fig. 5. (a) Schematic diagram of sectioning of resin-embedded catalyst to expose cross-sections. (b) AC-HAADF-STEM image of Cu@Si/SBA-15 after the ultrathin sectioning. The inserted figure is the particle size distribution. (c) Atomic-resolution image and the model of individual Cu particles in Cu@Si/SBA-15.

Fig. 6. Characterizations of Cu/SBA-15, Cu@Si/SBA-15, and Cs-Cu@Si/SBA-15. (a,b) Low-temperature (77 K) infrared transmission spectra. (c) FT k3-weighted Cu K-edge EXAFS spectra. (d-f) Wavelet transform for k3-weighted Cu K-edge EXAFS signals. Note: For all wavelet representations, the following set of parameters controls the WT resolution: σ = 1 and η = 7. Note that not all WT EXAFS are phase-corrected, which results in about 0.4 ? with respect to the actual radial distances.

Fig. 7. Characterization of Cu/SBA-15, Cs-Cu/SBA-15, Cu@Si/SBA-15, and Cs-Cu@Si/SBA-15. (a) The H2-TPR profiles. (b) XPS spectra of Cu 2p and peak fitting results. (c) Raman spectra.

Fig. 8. The reaction orders of C3H6 (a) and O2 (b) in C3H6 oxidation over Cs-Cu@Si/SBA-15. The reaction orders of C3H6 (c) and O2 (d) in C3H6 epoxidation for PO formation over Cs-Cu@Si/SBA-15. Reaction condition: Ftotal = 30 mL·min-1, Wcat = 50 mg, 250 °C. The in-situ IR spectra of Cu@Si/SBA-15 (e) and Cs-Cu@Si/SBA-15 (f,g) at 250 °C under a flowing mixture of N2, N2 + C3H6, and N2 + C3H6 + O2. Conditions: 0.01 g catalyst, C3H6:N2 = 1:9, C3H6:O2:N2 = 1:1:8, Ftotal = 50 mL·min-1, 1 atm).

Fig. 9. The key intermediates and reaction networks of C3H6 epoxidation on the Cu-O-Si interfaces. The arrows indicate the direction of electron transfer.

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Silica-confined Cu₂O nanoparticles for propylene epoxidation with molecular oxygen

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