Ni-based catalysts supported on Mg–Al hydrotalcites with different morphologies for CO2 methanation: exploring the effect of metal–support interaction

Abstract

Metal oxide supported Ni-based catalysts represent intensively studied materials for CO₂ methanation due to their relatively high activity, methane selectivity and low cost. However, the activity of Ni-based catalysts mainly depends on the nature of the used support during catalyst synthesis. Due to their good performance, hydrotalcite derived Mg–Al oxides have attracted significant attention as potential supports. However, the influence of support morphology on the active metal dispersion and catalytic performance has not yet been investigated. Hence, in order to study the effect of metal–support interaction, hydrotalcite derived Mg–Al supports with four different morphologies were designed and 20 wt% Ni was loaded as the active phase. The prepared materials were rigorously characterized by different techniques (XRD, SEM, FETEM, CO₂-TPD, etc.) to study properties such as crystallite size, Ni dispersion, morphologies, and basic sites. The catalytic activity, selectivity and long-term stability of these four catalysts were evaluated for CO₂ methanation (CO₂ : H₂ = 1 : 4) at different gas hourly space velocities, reaction temperatures, and reduction temperatures. Among the investigated catalysts, Ni/HT-10 i.e. 20 wt% Ni supported on the Mg–Al hydrotalcite with a “rosette-like” structure possesses superior CO₂ conversion (83.5%), a TOF of 13.5 min⁻¹ and 99.4% selectivity to CH₄ at 400 °C. This superior catalytic activity results from its high basicity, optimized pore size, and defined support structure which lead to good Ni dispersion as well as a high exposed metallic surface area after reduction. Furthermore, Ni/HT-10 allowed stable catalytic activity for around 120 h on stream.