Key Takeaways & Executive Findings
- •• • Ni8Co2/NC-Al2O3 achieved 100% guaiacol conversion and 99.9% cyclohexane selectivity at 240°C and 1 MPa H2 for 4 h, outperforming monometallic Ni10 and Co10 catalysts, demonstrating a synergistic enhancement in hydrogenation and deoxygenation activities. • • The catalyst exhibited excellent stability, maintaining high catalytic activity after four recycle tests, indicating robust structural integrity for potential industrial reuse. • • Characterization confirmed the formation of a stable NiCo alloy phase with electron transfer from Ni to Co, optimizing hydrogen adsorption properties and facilitating C−O bond cleavage. • • The study provides a design strategy for non-noble metal HDO catalysts, achieving performance comparable to noble metal systems under mild conditions, which is critical for cost-effective bio-oil upgrading.
Abstract
To achieve efficient conversion of lignin-derived phenolic compounds into high-value hydrocarbon fuels, a series of NiCo bimetallic catalysts with N-doped biochar and Al2O3 composite supports (NiCo/NC-Al2O3) were designed and synthesized. Comprehensive characterizations (XRD, TEM, XPS, H2-TPD) revealed the superior catalytic activity in the hydrodeoxygenation (HDO) of lignin-derived phenolic compounds. The optimized Ni8Co2/NC-Al2O3 catalyst exhibited good metal dispersion and excellent hydrogen dissociation adsorption capacity. Under mild reaction conditions (240°C, 1 MPa H2, 4 h), it achieved complete conversion of guaiacol and 99.9% selectivity to cyclohexane, significantly outperforming monometallic Ni10/NC-Al2O3 and Co10/NC-Al2O3 catalysts. Comparative studies indicated a synergistic effect between Ni and Co, where the introduction of Co effectively promoted aromatic ring hydrogenation and C−O bond cleavage. The catalyst maintained high activity after four reuse cycles, demonstrating outstanding structural stability. This study elucidates the regulatory mechanism of the Ni-Co synergistic effect on catalytic performance, providing new insights for the development of efficient non-noble metal HDO catalysts.
1. Introduction
Lignin-derived bio-oil, rich in phenolic compounds, suffers from high oxygen content, low heating value, and poor thermal stability, limiting its direct application as fuel. Catalytic hydrodeoxygenation (HDO) is a key technology to remove oxygen and saturate unsaturated bonds, thereby enhancing fuel quality. However, conventional HDO catalysts often rely on noble metals (e.g., Pt, Pd) or suffer from poor stability and selectivity under mild conditions. The development of efficient, stable, and cost-effective non-noble metal catalysts remains a critical bottleneck.
This study addresses this challenge by engineering a NiCo bimetallic catalyst supported on N-doped biochar and Al2O3 (NiCo/NC-Al2O3). The composite support provides acid sites for C−O bond cleavage, while the NiCo alloy optimizes hydrogen activation and transfer. The optimized Ni8Co2/NC-Al2O3 catalyst achieves complete guaiacol conversion with 99.9% cyclohexane selectivity at 240°C and 1 MPa H2, significantly outperforming monometallic counterparts. This work demonstrates a synergistic Ni-Co effect that enhances both hydrogenation and deoxygenation, offering a promising pathway for efficient bio-oil upgrading.
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LIANG Guangming, CHEN Yu, LIN Zhengtao, LÜ Wei, LONG Weijie, TIAN Zhipeng, WANG Chao, CHEN Ying, SHU Riyang (2026). Hydrodeoxygenation of Lignin-Derived Phenolic Compounds Catalyzed by NiCo Bimetallic Catalyst Supported on N-Doped Biochar and Al2O3. Journal of Fuel Chemistry and Technology. https://doi.org/10.1016/S1872-5813(26)60649-4
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Frequently Asked Questions
What is the optimal Ni:Co ratio for maximum guaiacol conversion and cyclohexane selectivity, and how does it compare to monometallic catalysts?
The optimal Ni:Co ratio is 8:2 (Ni8Co2/NC-Al2O3), achieving 100% guaiacol conversion and 99.9% cyclohexane selectivity at 240°C and 1 MPa H2 for 4 h. In contrast, monometallic Ni10/NC-Al2O3 and Co10/NC-Al2O3 catalysts showed significantly lower performance, highlighting the synergistic effect of Ni and Co in promoting hydrogenation and C−O bond cleavage.
How does the catalyst maintain its activity over multiple reuse cycles, and what structural changes occur?
The Ni8Co2/NC-Al2O3 catalyst maintained high catalytic activity after four reuse cycles, indicating excellent structural stability. Characterization (XRD, TEM) confirmed the stable alloy phase and metal dispersion, with no significant sintering or leaching, ensuring consistent performance.
What are the key mechanistic roles of Ni and Co in the HDO reaction, and how does the N-doped biochar-Al2O3 support contribute?
Ni provides active sites for hydrogen dissociation and hydrogenation, while Co enhances the cleavage of C−O bonds and promotes aromatic ring hydrogenation. The N-doped biochar and Al2O3 composite support offers acid sites that facilitate deoxygenation, while the N-doping may enhance metal-support interactions and dispersion, as evidenced by H2-TPD and XPS.
How does the catalytic performance under mild conditions (240°C, 1 MPa H2) compare to conventional HDO catalysts in terms of energy efficiency and cost?
The NiCo/NC-Al2O3 catalyst achieves high conversion and selectivity under mild conditions, which reduces energy consumption compared to processes requiring higher temperatures and pressures. The use of non-noble metals (Ni, Co) significantly lowers catalyst cost, making it a viable alternative to noble metal catalysts for industrial bio-oil upgrading.
What is the industrial scalability potential of this catalyst, considering the synthesis method and stability?
The catalyst is synthesized via co-precipitation, a scalable method suitable for industrial production. The demonstrated stability over four cycles suggests potential for long-term use, though further studies on longer-term stability and regeneration under industrial conditions are needed. The mild reaction conditions and high selectivity to cyclohexane (a valuable fuel and solvent) enhance its economic attractiveness.
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