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2026-08-06

*Separation and Purification Technology*: Research findings from the Zhao Chuanwen group at Nanjing Normal University in the field of biogas reforming.

Steam-Assisted Reforming of Biogas over CoLaAl Hydrotalcite-Derived Catalysts

Steam-assisted reforming of biogas over CoLaAl hydrotalcite-derived catalysts
First author
Weihao Fan
Corresponding author
Chuanwen Zhao

Research Highlights

  • A CoLaAl hydrotalcite-derived catalyst with highly dispersed active sites and a robust mesoporous structure was prepared by a hydrothermal method.
  • Introducing 25% steam activates a water-assisted oxygen cycle that enhances surface oxygen mobility and the gasification of carbonaceous species.
  • The catalyst sustains efficient CH4 and CO2 conversion for 20 h without measurable deactivation.
  • Stronger metal–support interactions improve structural stability, while the syngas H2/CO ratio is tuned to 1.5.

Introduction

In March 2026, Separation and Purification Technology published online the latest work from Professor Chuanwen Zhao’s team at Nanjing Normal University in the field of biogas reforming. The study reports a hydrothermally prepared CoLaAl hydrotalcite-derived catalyst and demonstrates that steam-activated oxygen cycling enables efficient, coke-resistant biogas reforming with a tunable product composition. Weihao Fan is the first author, and Chuanwen Zhao is the corresponding author.

Background

Converting biogas into syngas offers an effective route for utilizing the greenhouse gases CH4 and CO2. However, the high temperatures required for reforming readily promote severe carbon deposition and rapid catalyst deactivation. Introducing a controlled amount of steam enables combined steam–dry reforming: carbon deposits can be removed through in situ gasification, while the H2/CO ratio of the product gas can be adjusted for downstream applications.

In this study, an open-mesoporous CoLaAl hydrotalcite-derived catalyst was prepared by a hydrothermal method. At a steam concentration of 25%, a water-assisted oxygen cycle was activated on the catalyst surface. Continuously regenerated surface hydroxyl groups efficiently removed carbon-deposition precursors, allowing the catalyst to operate for 20 h without observable deactivation and producing syngas with an H2/CO ratio of 1.5. These results provide a practical basis for designing durable, coke-resistant bi-reforming catalysts with controllable product compositions.

Instrumentation Used in the Study

Perfectlight PLR-RP Series Photothermal Catalytic Reaction Evaluation System

Perfectlight PLR-RP Series Photothermal Catalytic Reaction Evaluation System

The PLR-RP system features a proprietary circumferential-illumination reactor in which the catalyst is arranged around the light source. This configuration increases the illuminated catalyst area from approximately 0.3 cm2 under flat illumination to about 20 cm2, enabling more complete contact between the catalyst and incident light. While maintaining effective light penetration, the catalyst loading volume can be increased from 0.9 to 9 mL. The design therefore improves light utilization, increases substrate adsorption capacity and conversion, and provides a new approach to scaling up industrial photothermal reaction systems.

Figure-by-Figure Analysis

Catalytic performance of CoLaAl-HT at different steam concentrations
Figure 1. Catalytic performance of CoLaAl-HT at different steam concentrations: (a) CH4 conversion, (b) CO2 conversion, and (c) H2/CO ratio. Key findings: Without steam, CH4 conversion is only approximately 55%. Increasing the steam concentration to 25% raises CH4 conversion to nearly 90% and the H2/CO ratio to 1.5, while maintaining stable CO2 conversion. An appropriate amount of steam gasifies carbon deposits in situ and protects the active sites. At 30% steam, however, CO2 conversion falls to approximately 70%, because excess steam intensifies competitive adsorption and promotes the water–gas shift reaction. A steam concentration of 25% therefore provides the best balance between catalytic activity and resistance to coking.
XPS spectra of CoLaAl-HT under different reforming atmospheres
Figure 2. XPS spectra of CoLaAl-HT: (a) Co 2p, (b) La 3d, (c) Al 2p, and (d) O 1s. Key findings: XPS analysis reveals pronounced changes in the surface chemical states of hydrothermally prepared CoLaAl under different atmospheres. During steam-free reforming, Co0 is oxidized by CO2 to Co3+, while La2O3 is converted into carbonate species. With 25% steam, the Co3+ fraction increases further and the La species evolve toward La(OH)3, whereas Al3+ remains structurally stable. The O 1s spectra show substantial increases in surface hydroxyl oxygen (OOH) and adsorbed oxygen (OS). These species establish a water-assisted oxygen cycle in which hydroxyl groups and adsorbed oxygen continuously gasify carbon deposits. The results demonstrate that steam enhances coke resistance and long-term stability by regulating the Co/La oxidation states and regenerating surface oxygen species.
SEM images of CoLaAl-HT after 20-hour stability tests with and without steam
Figure 3. SEM images of CoLaAl-HT after long-term testing: (a) 25% H2O and (b) 0% H2O. Key findings: After 20 h of reaction without steam, the catalyst surface is covered by abundant filamentous carbon generated through methane decomposition and the Boudouard reaction. The carbon filaments obstruct the pore network, promote particle agglomeration, cover active sites, and accelerate catalyst deactivation. By contrast, after reaction with 25% steam, the catalyst retains an intact, compact particulate morphology with no obvious filamentous or bulk carbon deposits. Steam therefore continuously gasifies the carbon species formed during reaction, preserving accessible active sites and long-term catalytic stability.
Thermogravimetric and Raman analyses of spent CoLaAl hydrotalcite-derived catalysts
Figure 4. Characterization of CoLaAl hydrotalcite-derived catalysts after long-term testing: (a) thermogravimetric analysis and (b) Raman spectroscopy. Key findings: Thermogravimetric analysis shows that the catalyst tested with steam contains only 6.5% carbon, far below the 20% measured after steam-free reforming. Desorption of adsorbed water occurs in the low-temperature region, mass gain associated with Co oxidation appears at intermediate temperatures, and carbon oxidation produces mass loss at high temperatures. Raman spectroscopy provides further confirmation: pronounced D, G, and 2D carbon bands are observed under steam-free conditions (ID/IG = 0.82), indicating the formation of highly graphitized carbon. With 25% steam, these carbon bands nearly disappear and bands associated with Co–O and La–O–Co structures emerge. Steam therefore suppresses graphitic-carbon deposition, promotes oxidative surface reconstruction, and facilitates carbon gasification, thereby maintaining stable active sites.

Summary

Steam-assisted reforming converts the CH4 and CO2 in biogas into value-added syngas while mitigating greenhouse-gas emissions. The principal challenge is rapid catalyst deactivation caused by carbon deposition under high-temperature conditions. In this work, an open-mesoporous CoLaAl hydrotalcite-derived catalyst was prepared hydrothermally, and steam was introduced to combine in situ coke removal with control of the syngas H2/CO ratio.

At an optimized steam concentration of 25%, a water-assisted oxygen cycle is activated on the catalyst surface. Regenerated hydroxyl groups continuously oxidize and remove newly formed carbon precursors. Consequently, the catalyst maintains high conversion without measurable deactivation over 20 h, while the H2/CO ratio remains at 1.5. The study offers a practical catalyst-design strategy for combined steam–dry reforming systems that require both durable coke resistance and controllable product composition.

Author Profile

Chuanwen Zhao is Professor, Doctoral Supervisor, and Vice Dean of the School of Energy and Mechanical Engineering at Nanjing Normal University. He has been recognized under the Jiangsu Province “Six Talent Peaks” program and as a young and middle-aged academic leader in the Jiangsu Universities “Qinglan Project.” His research supports China’s carbon-peaking and carbon-neutrality goals, with a long-standing focus on CO2 capture using solid sorbents and the catalytic conversion and utilization of carbon dioxide. As principal investigator, he has led multiple projects funded by the National Natural Science Foundation of China and major provincial or ministerial research programs. He has published more than 70 peer-reviewed papers in leading journals, including Applied Catalysis B: Environment and Energy, and has made sustained contributions to greenhouse-gas mitigation and carbon-resource utilization.

Publication Details

Weihao Fan, Ning Cai, Yiqian Yao, Xinzheng Wei, and Chuanwen Zhao. “Steam-assisted reforming of biogas over CoLaAl hydrotalcite-derived catalysts.” Separation and Purification Technology 394, Part 3 (2026): 137681. https://doi.org/10.1016/j.seppur.2026.137681

Publication information for the Separation and Purification Technology article

Founded in 2006, Beijing Perfectlight Technology Co., Ltd. (Perfectlight) is recognized as a National High-Tech Enterprise, a Zhongguancun High-Tech Enterprise, and one of Beijing’s first Specialized, Refined, Distinctive, and Innovative enterprises. The company is certified to ISO 9001, ISO 14001, and ISO 45001, and its after-sales service has achieved a five-star rating under GB/T 27922-2011. Perfectlight specializes in the research, development, manufacturing, sales, and service of intelligent, high-precision, high-performance instruments and integrated solutions. Its portfolio covers more than ten product families, including irradiation light sources; photocatalytic, photoelectrocatalytic, photothermal, and thermal catalytic systems; characterization and testing platforms; research and pilot-scale equipment; and photochemical synthesis systems. These solutions support the entire workflow from fundamental research and laboratory or pilot studies to industrial scale-up. Serving universities, research institutes, and industrial customers in new energy, pharmaceutical synthesis, fine chemicals, and advanced materials, Perfectlight products are used in more than 3,000 laboratories across nearly 50 countries and have supported over 9,000 SCI-indexed publications. The company has led or participated in the development of national and industry standards, undertaken projects under China’s National Key R&D Program, secured multiple core intellectual-property rights and Beijing New Technology and New Product certifications, and helped industrial customers establish tonne-scale and 100-tonne-scale photochemical production lines.

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