Highly dispersed MoOx-Ru/C bimetallic catalyst for efficient hydrogenolysis of esters to alkanes

doi:10.1016/S1872-2067(24)60254-8

Abstract

Abstract:

The efficient hydrogenolysis of esters to alkanes is the key protocol for producing advanced biofuels from renewable plant oils or fats. Due to the low reactivity of the carbonyl group in esters, a high reaction temperature (>250 °C) is the prerequisite to ensure high conversion of esters. Here, we report a highly dispersed MoO_x-Ru/C bimetallic catalyst for the efficient hydrogenolysis of esters to alkanes under 150 °C. The optimal catalyst exhibits >99% conversion of methyl stearate and 99% selectivity to diesel-range alkanes, reaching a high rate of up to 2.0 mmol g_cat^-1 h^-1, 5 times higher than that of Ru/C catalyst (MoO_x/C is inert). Integrated experimental and theoretical investigations attribute the high performance to the abundant MoO_x-Ru interfacial sites on the catalyst surface, which offers high activity for the C-O cleavage of esters. Furthermore, the dispersed MoO_x species significantly weaken the hydrocracking activity of the metallic Ru for C-C bonds, thus yielding alkane products without carbon loss. This study provides a facile and novel strategy for the design of high-performance heterogeneous catalysts for the hydrodeoxygenation of biomass-derived esters to alkane products.

Key words: Bimetallic catalyst, Interface engineering, Hydrodeoxygenation, Fatty esters, Diesel-range alkanes

Xincheng Cao, Jiaping Zhao, Feng Long, Peng Liu, Yuguo Dong, Zupeng Chen, Junming Xu, Jianchun Jiang. Highly dispersed MoO_x-Ru/C bimetallic catalyst for efficient hydrogenolysis of esters to alkanes[J]. Chinese Journal of Catalysis, 2025, 71: 256-266.

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URL: https://www.cjcatal.com/EN/10.1016/S1872-2067(24)60254-8

https://www.cjcatal.com/EN/Y2025/V71/I4/256

Figures/Tables 9

Fig. 1. (a) XRD patterns of the prepared catalysts. TEM (b), HRTEM (c), AC-HAADF-STEM (d) images, and the corresponding 2D pseudo-color surface plot (e) of 0.2 MoOx-Ru/C. (f) CO pulse adsorption profiles of the prepared catalysts. (g-i) STEM-associated EDX elemental mapping images of 0.2 MoOx-Ru/C.

Fig. 2. (a) Mo K-edge XANES spectra of 0.2 MoOx-Ru/C and reference samples. (b) Mo 3d XPS spectra of 0.2 MoOx-Ru/C and MoO3. (c) Mo K-edge FT-EXAFS spectra of 0.2 MoOx-Ru/C and reference samples. (d) R-space fitting results of the EXAFES spectra of 0.2 MoOx-Ru/C catalyst. Wavelet transform of Mo K-edge data: 0.2 MoOx-Ru/C (e), Mo foil (f), MoO2 (g), and MoO3 (h). (i) Schematic diagrams of the MoOx-Ru. Ru, yellow; O, red; Mo, blue.

Fig. 3. (a) FTIR spectra of pyridine adsorption at 150 °C. (b) FTIR spectra of acetonitrile-d on Ru/C, 0.2 MoOx-Ru/C and 0.2 MoOx-Ru/C (N2). XPS spectra of Mo 3d (c) and O 1s (d) for 0.2 MoOx-Ru/C and 0.2 MoOx-Ru/C (N2) catalysts.

Fig. 4. (a) Catalyst screening. (b) Effect of MoOx loadings upon the HDO of methyl stearate. (c) Reaction rate and formation rate of alkanes over Ru/C and 0.2 MoOx-Ru/C. (d) Comparison of the catalytic performance of 0.2 MoOx-Ru/C with the state-of-the-art catalysts for the HDO of fatty esters (details in Table S3). Reaction conditions: 0.1g reactant, 0.03 g catalyst, 150 °C, 3.0 MPa H2, 6.0 h, and 10 mL n-hexane.

Fig. 5. (a) Conversion and product distribution along with reaction time over 0.2 MoOx-Ru/C at 150 °C. Effect of reaction temperature (b) and product distributions versus time (c) at 205 °C over Ru/C and 0.2 MoOx-Ru/C. (d) Reaction network for the HDO of fatty acid esters over the Ru/C and MoOx-Ru/C. Reaction conditions: 0.1 g reactant, 0.03 g catalyst, 150 °C, 3.0 MPa H2, 6.0 h, 10 mL n-hexane.

Table 1 The substrate scope of various esters over 0.2 MoOx-Ru/C catalyst.

Entry	T (°C), t (h)	Con. (%)	Selectivity (%)
1	150, 6.0	>99.0	n-C₉H₁₉-CH₃ 74.8 n-C₉H₂₀ 24.6
2	150, 6.0	96.3	n-C₁₁H₂₃-CH₃ 72.1 n-C₁₁H₂₄ 27.5
3	150, 6.0	>99.0	n-C₁₅H₃₁-CH₃ 76.7 n-C₁₅H₃₂ 22.1
4	150, 6.0	>99.0	n-C₁₇H₃₅-CH₃ 76.8 n-C₁₇H₃₆ 23.2
5	150, 6.0	>99.0	n-C₁₈H₃₇-CH₃ 71.1 n-C₁₈H₃₈ 23.0
6	150, 6.0	>99.0	n-C₁₅H₃₁-CH₃ 68.9 n-C₁₅H₃₂ 31.1
7	150, 6.0	>99.0	n-C₁₇H₃₃-CH₃ 67.1 n-C₁₇H₃₄ 31.5
8	150, 6.0	>99.0	n-C₁₇H₃₃-CH₃ 67.6 n-C₁₇H₃₄ 31.7
9	150, 6.0	>99.0	C₁₁H₂₃-CH₃ 67.5 C₁₁H₂₄ 30.7
10	140, 6.0	>99.0	C₁₀H₁₉-CH₃ 60.4 C₁₀H₂₂ 23.9

Fig. 6. (a) TPD analysis of methyl octanoate over Ru/C and 0.2 MoOx-Ru/C catalysts. DRIFTS spectra of methyl octanoate adsorption over Ru/C (b) and 0.2 MoOx-Ru/C (c) catalysts. (d) The adsorption energy of methyl propionate over the Ru (001) and Ru-Mo3O7. The kinetic barriers of methyl propionate conversion over Ru-Mo3O7 (e) and Ru (001) (f). Ru: purple; Mo: light green; O: red; H: white; C: dark gray.

Fig. 7. The HDO reaction mechanism of fatty esters over the MoOx-Ru/C.

Fig. 8. TPD of heptane (a), and the associated decomposition product of H2 (b), CH4 (c), and C3H8 (d) over Ru/C, 0.2 MoOx-Ru/C, and 0.5 MoOx-Ru/C. (e) The diagram of the reduced hydrocracking of alkanes over MoOx-Ru/C compared to Ru/C catalyst.

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