Dry reforming of methane in molten manganese chloride mixtures

The dry reforming reaction converts two major greenhouse gases (CH₄ and CO₂) into valuable syngas (CO and H₂). However, the use of conventional solid catalysts in the dry reforming process suffers from catalyst deactivation due to carbon deposition and the limitation of a fixed 1:1 CH₄-CO₂ feed ratio. We present here a study using a molten mixture of manganese chloride and potassium chloride (MnCl₂-KCl) for dry reforming. This system offers three key advantages: enhanced catalytic activity, avoidance of catalyst deactivation, and flexibility to utilize non-stoichiometric CH₄-CO₂ feed combinations. Experimental findings demonstrated that the MnCl₂-KCl system exhibited significant catalytic activity, with activation energies of 260 ± 20 kJ∙mol⁻¹ for CH₄ and 170 ± 20 kJ∙mol⁻¹ for CO₂. A stability test confirmed the resistance to catalyst deactivation for 40 h and the utilization of various feed compositions beyond the stoichiometric 1:1 CH₄-CO₂ ratio, allowing adjustment of the produced syngas composition. In addition, the solid carbon formed from side reactions showed a partially crystalline structure after water washing, suggesting its value-added potential. Simulations demonstrated that CH₄ activation at the modeled liquid surfaces of molten MnCl₂ and MnCl₂-KCl constituted the rate-determining step, with MnCl₂ presenting a reduced activation barrier. Both surfaces promoted CH₃ oxidation and hydroxylation rather than total dehydrogenation. These combined experimental and computational findings highlight the molten MnCl₂-KCl catalyst as a sustainable alternative to the conventional dry reforming catalyst.