Synergistic Effect of Group 9 Metals on the Performance of Hydrotalcite-Derived Ni Catalysts for Methane Dry Reforming.

Dry reforming of methane (DRM) offers an efficient pathway for the simultaneous utilization of CO2 and CH4, two of the most impactful greenhouse gases, through their conversion into valuable synthesis gas. Nevertheless, the practical deployment of DRM remains challenged by catalyst deactivation, predominantly caused by carbon accumulation and metal sintering. In this work, we explore the impact of group 9 metal promoters, specifically iridium (Ir), cobalt (Co), and rhodium (Rh), on the catalytic behavior and stability of nickel-based materials derived from hydrotalcite precursors. The catalysts were synthesized via a coprecipitation method and thoroughly characterized using a combination of structural, morphological, and surface analytical techniques, alongside hydrogen temperature-programmed reduction (H2-TPR) and temperature-programmed desorption analyses for CO2 (CO2-TPD) and NH3 (NH3-TPD). Catalytic testing was conducted at 750 °C over a 20-h period. The addition of Ir and Rh was found to markedly enhance Ni dispersion, strengthen metal-support interactions, and increase the abundance of strong basic sites, all contributing to reduced carbon formation. Among the catalysts, NiHT-Ir demonstrated the highest stability and activity, maintaining CH4 and CO2 conversions above 80% with minimal deactivation. NiHT-Rh similarly exhibited excellent catalytic performance and coke resistance. By contrast, NiHT-Co showed a decline in performance associated with severe Ni sintering, while the monometallic NiHT catalyst suffered rapid deactivation. Post-reaction analyses confirmed that Ir and Rh effectively limited coke deposition and metal aggregation, whereas Co promoted Ni particle growth. Density functional theory (DFT) calculations were carried out to elucidate the variations in adsorption behavior of CH4 and CO2 across the different catalyst surfaces. This study underscores the beneficial role of group 9 metals, particularly Ir and Rh, in enhancing the catalytic efficiency, stability, and resistance to the deactivation of hydrotalcite-derived Ni-based catalysts for DRM.