Key Takeaways & Executive Findings
- •• • LSON-50 pellets achieve 0.330 g/g CO2 capacity at 650 °C under 15 vol% CO2, a 4.1-fold increase over unmodified LSO-0 (0.080 g/g), directly addressing the diffusion-limited performance of densified pellets in fluidized bed reactors. • • After 50 adsorption–desorption cycles, LSON-50 retains 0.284 g/g (86% of initial capacity), demonstrating cyclic stability that meets industrial thresholds for long-term operation without frequent sorbent replacement. • • Attrition loss remains below 10% for LSON-50, satisfying mechanical durability requirements for fluidized bed systems where excessive fines generation leads to pressure drop and material loss. • • SCG loading of 50 wt% (LSO-50) yields 0.275 g/g without external Na doping, confirming that the biomass alone provides the primary performance enhancement; LSON-70 is excluded due to insufficient mechanical stability, highlighting a trade-off between porosity and pellet integrity.
Abstract
Practical deployment of Li4SiO4 as a high-temperature CO2 sorbent requires pelletization, which inevitably densifies the microstructure and imposes severe CO2 diffusion limitations. Conventional sacrificial pore-forming agents address this issue but remain single-purpose, serving solely as structural templates without conferring chemical benefits. Here, we demonstrate that spent coffee grounds (SCGs), an abundant food-industry waste, can serve as a single-source modifier that achieves three colocalized enhancements in Li4SiO4 pellets: hierarchical pore engineering, in situ K-doping, and oxygen vacancy generation. The thermal decomposition of SCG creates an interconnected hierarchical macroporous network that effectively reduces intraparticle CO2 diffusion resistance. Meanwhile, the mineral-rich SCG ash provides in situ potassium doping, generating a localized eutectic molten carbonate phase that accelerates liquid-phase ion transport. Crucially, the transient reducing atmosphere during biomass combustion introduces oxygen vacancies into the silicate lattice; density functional theory (DFT) calculations reveal that these vacancies serve as highly active CO2 adsorption sites with a strongly exothermic adsorption energy of −0.914 eV. Benefiting from this triple-synergistic enhancement, the SCG-modified sorbent (LSO-50) achieves a CO2 adsorption capacity of 0.275 g/g at 650 °C under 15 vol% CO2, representing a more than fourfold improvement over unmodified pellets. When further combined with Na2CO3 codoping to promote additional eutectic formation, the optimized sorbent (LSON-50) reaches 0.330 g/g, retains 0.284 g/g after 50 adsorption–desorption cycles, and exhibits robust mechanical stability (< 10% attrition loss). By colocating structural, chemical, and defect features within a single biomass-derived modifier, this work establishes a scalable waste-valorization route for high-performance, eco-friendly CO2 capture.
1. Introduction
The escalating concentration of atmospheric CO2 has intensified the urgency for developing efficient carbon capture technologies. Among solid sorbents, lithium orthosilicate (Li4SiO4) has emerged as a promising candidate for high-temperature CO2 capture, owing to its high theoretical adsorption capacity of 36.7 wt%, excellent thermal stability, and more favorable thermodynamics compared to calcium-based sorbents. However, practical deployment in industrial fluidized bed reactors is hindered by intrinsic engineering trade-offs. Fine powders exhibit superior kinetics in laboratory settings, but industrial applications mandate robust pellets to prevent elutriation and minimize pressure drop. Densification of powders into mechanically stable ceramic pellets during high-temperature sintering inevitably reduces specific surface area, increasing intraparticle diffusion resistance of CO2 and resulting in sluggish adsorption kinetics and reduced conversion efficiency over prolonged cycling.
To alleviate these diffusion limitations, researchers have extensively explored sacrificial pore-forming agents into Li4SiO4 precursors to engineer porous structures. For instance, graphite molding has been employed, but such conventional agents remain single-purpose, serving solely as structural templates without conferring chemical benefits. This limitation motivates the search for multifunctional modifiers that can simultaneously address structural, chemical, and defect-related bottlenecks. Here, spent coffee grounds (SCGs), an abundant food-industry waste, are demonstrated as a single-source modifier that achieves three colocalized enhancements: hierarchical pore engineering, in situ potassium doping, and oxygen vacancy generation. The thermal decomposition of SCG creates an interconnected macroporous network, while mineral-rich ash provides potassium doping and a transient reducing atmosphere introduces oxygen vacancies. This triple-synergistic mechanism yields LSON-50 with 0.330 g/g capacity at 650 °C, 86% capacity retention after 50 cycles, and <10% attrition loss, establishing a scalable waste-valorization route for high-performance CO2 capture.
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TANG Leiqing, JIANG Haoyu, ZHANG Hongping, HUANG Zhangyi, WANG Haomin, WANG Qingyuan, QI Jianqi, CHEN Ruichong (2026). Spent coffee grounds as multifunctional modifiers for triple-synergistic enhancement of Li4SiO4 ceramic sorbents in high-temperature CO2 capture. Journal of Advanced Ceramics. https://doi.org/10.26599/JAC.2026.9221339
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Frequently Asked Questions
What is the primary failure mechanism of Li4SiO4 pellets under industrial fluidized bed conditions, and how does SCG modification mitigate it?
The primary failure mechanism is diffusion limitation caused by densification during pelletization, which reduces specific surface area and increases intraparticle CO2 diffusion resistance, leading to sluggish kinetics and reduced conversion. SCG modification mitigates this by creating an interconnected hierarchical macroporous network that reduces diffusion resistance, as evidenced by LSO-50 achieving 0.275 g/g at 650 °C under 15 vol% CO2, a more than fourfold improvement over unmodified pellets.
How does the mechanical stability of LSON-50 compare to industrial requirements for fluidized bed reactors?
LSON-50 exhibits attrition loss below 10%, which meets the typical industrial threshold for mechanical durability in fluidized bed systems. This is critical because excessive attrition leads to fines generation, pressure drop, and material loss. However, LSON-70 was excluded due to insufficient mechanical stability, indicating that SCG loading must be optimized to balance porosity and pellet integrity.
What is the role of oxygen vacancies in enhancing CO2 adsorption, and what is the quantitative evidence?
Oxygen vacancies, generated through localized carbothermic reduction during SCG combustion, serve as highly active CO2 adsorption sites. Density functional theory (DFT) calculations reveal a strongly exothermic adsorption energy of −0.914 eV for these vacancies, significantly enhancing CO2 chemisorption. This contributes to the overall capacity improvement, with LSO-50 reaching 0.275 g/g without external Na doping.
How does the cyclic stability of LSON-50 compare to conventional Li4SiO4 sorbents, and what are the implications for long-term operation?
LSON-50 retains 0.284 g/g after 50 adsorption–desorption cycles, corresponding to 86% of its initial capacity (0.330 g/g). This high retention indicates resistance to sintering and degradation, which is essential for reducing sorbent replacement frequency and operational costs in industrial CO2 capture. The stability is attributed to the hierarchical porous structure that buffers product shell expansion and the eutectic molten phase that facilitates ion transport.
What are the scalability and cost implications of using spent coffee grounds as a modifier for Li4SiO4 sorbents?
Spent coffee grounds are an abundant, low-cost food-industry waste, making them a scalable and economically viable modifier. The single-source modification eliminates the need for multiple additives, simplifying production. The optimized LSON-50 achieves 0.330 g/g capacity with <10% attrition loss, demonstrating a practical balance between performance and mechanical stability. However, LSON-70 was excluded due to insufficient mechanical stability, highlighting that loading must be optimized for industrial scalability.
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