Sol–gel-prepared ternary Ni–Ce–Mg–O oxide systems: the role of CeO₂ in balancing between dry reforming of methane and pyrolysis of hydrocarbons

In this study, the modified alkoxide sol–gel approach was used for the synthesis of ternary Ni–Ce–Mg–O oxide systems of variable composition. The prepared samples were characterized by thermal analysis, low-temperature nitrogen adsorption, transmission electron microscopy, X-ray diffraction, and temperature-programmed reduction. The presence of CeO₂ in the oxide composition was found to affect such properties as texture, morphology, reducibility of Ni²⁺, and dispersion of Ni⁰ in the reduced samples. The catalytic properties of the Ni–Ce–Mg–O samples were examined with regard to dry reforming of methane (DRM) and catalytic pyrolysis of hydrocarbons with the formation of carbon nanofibers (CNF). It was found that the CeO₂-containing samples demonstrate more stable performance in DRM and are less prone to coke formation. The Ni10Ce10 catalyst containing 10% NiO and 10% CeO₂ within the MgO matrix demonstrated the highest CO₂ and CH₄ conversion values. Contrarily, the highest carbon yield was observed for the Ni15Ce5 sample (15 wt% NiO, 5 wt% CeO₂). An increase in the CeO₂ content diminished the carbon yield. The structure of the formed CNFs was affected by the type of substrate used (ethylene or a mixture of C₂-C₄ saturated hydrocarbons). Thus, the sol–gel technique was shown to be efficient for the preparation of ternary Ni–Ce–Mg–O systems with a high content of nickel and ceria species evenly distributed within the MgO matrix. Varying the ceria content, it is possible to balance between the DRM and catalytic pyrolysis modes of the catalyst operation.