Methanation of CO2 over nickel and molybdenum bi-metallic catalyst system supported on activated carbon

Abstract

The escalating environmental impact of CO₂ emissions has driven the demand for innovative solutions to capture and convert CO₂ into useful energy forms, with CO₂ methanation standing out as a viable approach for generating methane (CH₄) as a clean fuel. This research focuses on developing and evaluating bimetallic Ni–Mo catalysts supported on activated carbon (AC) for CO₂ methanation, exploring the effects of Mo concentration and synthesis techniques on catalytic performance. The catalysts, synthesized with a Ni base of 13 wt.% and Mo as a promoter (5–11 wt.%), were prepared using three distinct methods: incipient wetness impregnation (IWI), sol-gel (SG), and mechanical mixing (MM). These methods provided a range of catalyst properties, allowing for a thorough investigation of how synthesis conditions influence activity, stability, and CO₂-to-CH₄ conversion efficiency. Advanced characterization techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) surface area analysis, and X-ray photoelectron spectroscopy (XPS), were employed to reveal the structural, morphological, and electronic properties of the catalysts. The introduction of Mo significantly modified the Ni/AC catalyst, enhancing pore size, and active site dispersion. Results indicated that optimal Mo concentration, specifically 7 wt.%, improved Ni dispersion and electron transfer properties, reducing the catalyst’s activation energy for CO₂ methanation to 54.6 kJ/mol, compared to 115 kJ/mol for undoped Ni/AC. This facilitated superior catalytic activity, with Ni-7%Mo/AC achieving a high CO₂ conversion rate of 92% and CH₄ selectivity of 80% at a moderate reaction temperature of 250 °C. Among the preparation techniques, the incipient wetness impregnation (IWI) method yielded the most promising results, with the Ni-7%Mo/AC catalyst synthesized via IWI showing the highest CO₂ conversion (56%) and (>95%) CH₄ selectivity at 350 °C. This enhanced performance is attributed to improved metal dispersion, stronger metal-support interactions, and structural stability, resulting from the IWI method. The sol-gel and mechanical mixing methods, while effective, demonstrated lower CO₂ conversion rates of 51.4% and 51.2%, respectively, under similar conditions. These variations highlight the critical role of synthesis techniques in optimizing catalyst performance for CO₂ methanation.

To complement the experimental findings, an informetric analysis was conducted on global research trends in molybdenum-enhanced Ni-based catalysts for CO₂ methanation. This analysis utilized VOSviewer and RStudio to identify publication trends, collaboration networks, and research focus areas across highly cited studies from 1994 to 2023. The results highlighted an increasing interest in Mo-doped Ni catalysts, particularly for their ability to enhance CO₂ methanation activity, stability, and resistance to deactivation through sintering and coking. The bibliometric insights highlighted the relevance of Mo in creating efficient, long-lasting catalysts and identified key contributors and leading publications in the field. A review of AC-based materials further illustrated their potential for sustainable CO₂ methanation applications, emphasizing AC’s large surface area, porosity, and cost effectiveness as a catalyst support. The role of AC in enhancing catalyst stability and facilitating CO₂ adsorption positions it as an ideal material for carbon capture and utilization (CCU) technologies. Despite these advantages, challenges remain in optimizing the catalyst formulation for industrial-scale applications, particularly in maintaining stability and minimizing energy requirements. Conclusively, this study demonstrates that Ni-7%Mo/AC, synthesized via incipient wetness impregnation, is an optimal catalyst for CO₂ methanation, achieving high efficiency in converting CO₂ to CH4. These findings not only advance the understanding of CO₂ methanation over Ni-Mo catalysts but also establish a foundation for scaling up this process to support global sustainability goals.