Why Catalyst Dispersion Matters in Dry Reforming of Biogas

This article presents a rigorous investigation into the impact of the charge-enhanced dry impregnation (CEDI) technique on the physicochemical characteristics and catalytic performance of a ceria-supported nickel-based catalyst. The main goal of the CEDI technique was to enhance the electrostatic adsorption of the nickel precursor onto the ceria support surface during dry impregnation (DI).

For an in-depth comparative evaluation, two distinct catalyst samples were synthesized: 10Ni/CeO₂-CEDI, prepared using the CEDI technique, and 10Ni/CeO₂-DI, prepared using the traditional DI technique, which served as the control.

Both catalysts were analyzed under biogas dry reforming (BDR) conditions to produce synthesis gas. The evaluation focused on key performance metrics, including model-biogas feed conversion (X_CH4 and X_CO2), desirable product selectivity (S_H2, S_CO), and byproducts (H₂O, C), as well as the propensity and type of undesirable carbon formed on the catalysts.

Figure 1. H₂-TPR (temperature-programmed reduction) profiles for NiO, CeO₂, and the 10Ni/CeO₂-DI and 10Ni/CeO₂-CEDI catalysts. Image Credit: Hiden Analytical

Characterization and Performance Improvement

To determine the impact of the CEDI preparation method, both fresh and spent catalysts were systematically characterized using a range of analytical techniques.

These methods encompassed structural evaluation via X-ray diffraction (XRD), surface area and porosity assessment using adsorption/desorption, and surface electronic state investigation via X-ray photoelectron spectroscopy (XPS).

In addition, microscopic analysis was carried out via scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to identify particle morphology and properties.

Complementary evaluations were performed using a Hiden Analytical CATLAB microreactor equipped with a quadrupole mass spectrometer (QMS) featuring Faraday and SEM detectors. These analyses probed the critical physicochemical characteristics directly influenced by the CEDI synthesis technique.

These included: H₂ chemisorption to quantify active-site dispersion, temperature-programmed reduction (H₂-TPR) to evaluate the metal-support interaction and the catalyst's bulk-phase reducibility, and oxygen-temperature-programmed oxidation (O₂-TPO) to assess carbon deposited on the catalysts.

Figure 2. O₂- TPO profiles of 10Ni/CeO₂-DI and 10Ni/CeO₂-CEDI catalysts synthesized by DI and CEDI methods. The experimental conditions for these results include a model biogas feed ratio of CH₄/CO₂=1, GHSV of 7500 mL/h⋅g_cat, and a reaction time of seven hours. Image Credit: Hiden Analytical

Figure 3. CO₂ conversion at temperatures of 800 °C, 850 °C, and 900 °C. The experimental conditions for these results include a model biogas feed ratio of CH₄/CO₂=1, a gas hourly space velocity (GHSV) of 7500 mL/h⋅g_cat, and a reaction time of seven hours. Image Credit: Hiden Analytical

Key Findings and Conclusion

The experimental results clearly demonstrated that the CEDI technique effectively enhanced electrostatic interactions between the nickel precursor and the ceria support. This improved interaction produced superior structural and electronic characteristics in the 10Ni/CeO₂-CEDI catalyst.

Specifically, the CEDI preparation markedly reduced the average nickel nanoparticle size to 3.33 nm, substantially smaller than that observed in the control DI-prepared catalyst.

This size reduction directly caused a significant improvement in active metal dispersion, increasing from a mere 1.4% in the 10Ni/CeO₂-DI catalyst to a high of 5.04% in the CEDI-prepared counterpart.

A stronger metal-support interaction was further demonstrated by a discernible positive shift in the TPR reduction temperature, increasing from 290 °C for the control catalyst to 340 °C for the catalyst prepared via the CEDI technique.

Together, these superior physicochemical characteristics directly correlated with improved catalytic performance under biogas reforming conditions. The 10Ni/CeO₂-CEDI catalyst demonstrated both a higher biogas conversion efficiency and a significant reduction in the rate of carbon deposition.

These findings confirm that the CEDI technique offers an effective and promising strategy for synthesizing highly active and stable supported nickel catalysts for efficient syngas production via biogas dry reforming reaction.

Figure 4. CH₄ conversion at temperatures of 800 °C, 850 °C, and 900 °C. The experimental conditions for these results include a model biogas feed ratio of CH₄/CO₂=1, a gas hourly space velocity (GHSV) of 7500 mL/h⋅g_cat, and a reaction time of seven hours. Image Credit: Hiden Analytical

Figure 5. The H₂ selectivity at temperatures of 800 °C, 850 °C, and 900 °C. The experimental conditions for these results include a model biogas feed ratio of CH₄/CO₂=1, a gas hourly space velocity (GHSV) of 7500 mL/h⋅g_cat, and a reaction time of seven hours. Image Credit: Hiden Analytical

Figure 6. The CO selectivity at temperatures of 800 °C, 850 °C, and 900 °C. The experimental conditions for these results include a model biogas feed ratio of CH₄/CO₂=1, a gas hourly space velocity (GHSV) of 7500 mL/h⋅g_cat, and a reaction time of seven hours. Image Credit: Hiden Analytical

Acknowledgments

Produced from materials originally authored by Babusi Balopi, Institute for Catalysis and Energy Solutions (ICES), University of South Africa.

References and Further Reading:

1. Babusi Balopi., et al. (2024). Dry reforming of model-biogas over ceria-supported nickel catalyst: the effect of charge enhanced dry impregnation on the catalytic performance and coke resistance. Research on Chemical Intermediates, 50(9), pp.4175–4198. DOI: 10.1007/s11164-024-05362-x. https://link.springer.com/article/10.1007/s11164-024-05362-x.

This information has been sourced, reviewed, and adapted from materials provided by Hiden Analytical.

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