Fe-based catalyst for thermo-catalytic CO2 hydrogenation into ethanol: The essential role of water management and Fe-based carbide/oxide ratio

doi:10.1016/S1872-2067(26)65065-6

Abstract

Abstract:

CO₂ hydrogenation to ethanol represents a pivotal pathway for valuable utilization of greenhouse gas CO₂, yet conventional catalysts are still limited by active-phase instability and undesirable byproduct selectivity. Herein, we propose a dual-components catalyst system synergized by hydrophobic carbon-encapsulated Fe-based catalyst (NaFe@C) and K modified CuZnAl component (KCZA), which achieves ultra-high ethanol selectivity of 35% under optimized conditions (5 MPa and 320 °C). KCZA initiates the CO₂ activation via reverse water-gas shift reaction and supplies oxygen-containing intermediates (mainly CH_xO*, x = 0, 1, or 2). NaFe@C component is mainly responsible for the C-O activation for CH_x* formation and C-C coupling between CH_x* and CH_xO*, as well as the following hydrogenation step for ethanol synthesis. Notably, the hydrophobic carbon shell in NaFe@C plays a critical role in tailoring the oxidation behaviors of Fe-based active sites and optimizing the phase ratio of Fe₃O₄/χ-Fe₅C₂ via water management. Multiple characterization and theoretical simulation results clarify that the unique electronic property of Fe-based active sites endowed by the optimized phase ratio is beneficial to boost the ethanol synthesis performance by balancing the coverage of key intermediates and lowering the energy barrier of essential steps. This work is promising to provide guidance for the rational design of advanced catalysts for targeted transformation of CO₂ or syngas into ethanol and beyond.

Key words: CO₂ hydrogenation, Dual-components catalysis, Ethanol synthesis, Water management, Active phase dynamic regulation

Xiaojie Liu, Zhifu Yu, Qi Li, Yang Wang, Xinze Bi, Kaixuan Huo, Dingyao Li, Zhiang Yuan, Yifan Yan, Shibin Li, Yiwu Lu, Qiang Liu, Wenhang Wang, Mingbo Wu. Fe-based catalyst for thermo-catalytic CO₂ hydrogenation into ethanol: The essential role of water management and Fe-based carbide/oxide ratio[J]. Chinese Journal of Catalysis, 2026, 86: 112-124.

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URL: https://www.cjcatal.com/EN/10.1016/S1872-2067(26)65065-6

https://www.cjcatal.com/EN/Y2026/V86/I7/112

Figures/Tables 8

Fig. 1. Structural characterization and surface properties. TEM (a,b) and HRTEM (c) images of the NaFe@C catalyst. (d) HAADF-STEM image of the spent NaFe@C catalyst and the corresponding elemental mapping images of Fe, C, and Na elements. (e) H2O droplet contact angle tests.

Fig. 2. Catalytic performance of CO2 hydrogenation to ethanol. (a) CO2 conversion and product selectivity of four catalysts. (b) Comparison of CO2 conversion and ethanol selectivity from NaFe@C&KCZA with the results reported in other literature. Reaction conditions: 320 °C, 5 MPa (31.7% CO2, 63.3% H2, and 5.0% Ar), 15 mL min-1, and time on stream (TOS) = 8 h. Catalyst weight: 0.3 g of NaFe catalyst, 0.36 g of NaFe@C catalyst, NaFe&KCZA (total weight: 0.6 g), or NaFe@C&KCZA (total weight: 0.66 g). The two catalyst powders were mixed and granulated (20-40 mesh) and mixed with an equal volume of quartz sand in the reactor.

Fig. 3. Catalyst characterization. (a) XRD patterns of post-reaction catalysts. 57Fe M?ssbauer spectra of NaFe (b), NaFe@C (c), NaFe&KCZA (d), and NaFe@C&KCZA (e) catalysts after catalytic testing.

Fig. 4. Schematic diagrams of H2O microenvironment regulation by NaFe (a), NaFe@C (b), NaFe&KCZA (c), and NaFe@C&KCZA (d) catalysts. The phase compositions of Fe-based active sites tailored by H2O management are also given.

Fig. 5. In-situ XRD patterns of NaFe@C&KCZA catalyst under H2 reduction (a) and carburizing (b) atmospheres.

Fig. 6. CO-DRIFTS of the reference sample dominated by χ-Fe5C2 phase (a), spent NaFe@C&KCZA catalyst (b), and spent NaFe@C catalyst (c).

Fig. 7. (a) In-situ DRIFT spectra of high-pressure (3 MPa) CO2 hydrogenation reaction on NaFe@C&KCZA catalyst. (b) Reaction pathway for ethanol synthesis from CO2 hydrogenation.

Fig. 8. Theoretical simulations and mechanistic analysis of ethanol synthesis via Fe-based catalysts. (a) Differential charge density plots of χ-Fe5C2, Fe3O4/χ-Fe5C2 (M), and Fe3O4/χ-Fe5C2 (H) models. The yellow and cyan electron clouds represent electron accumulation and depletion, respectively. (b) Valence electron counts for Fe-based species in the three models. Species evolution from CO to CH2* (c) and the energy profiles (d) for C-C coupling between CH2* and CO*, and the subsequent hydrogenation steps via the three models. Key: transition state (TS), Fe (purple), C (dark gray), O (red), and H (white).

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Fe-based catalyst for thermo-catalytic CO₂ hydrogenation into ethanol: The essential role of water management and Fe-based carbide/oxide ratio

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