• Co addition to Ni/Mg-substituted hydroxyapatite forms Ni-Co alloys, enhancing metal-support interactions and Ni dispersion.
• Optimal Co loading improves catalytic activity and stability in dry reforming of methane, while excess Co leads to metal agglomeration.
• Co reduces graphitic carbon deposition, a key factor for improved catalyst stability.
• The study provides insights for designing efficient Ni-based catalysts for DRM, contributing to carbon neutralization efforts.