Basicity as a descriptor for catalyst performance: a promoter study for syngas production via autothermal reforming of methane with CO2

Abstract

Autothermal reforming (ATR) of methane with CO2 is a technologically critical process for the production of syngas with tunable H-2/CO ratios, combining endothermic reforming and exothermic oxidation in a single energy-neutral reactor. The inherent high temperatures and oxidative environment, however, present severe challenges for catalyst stability. This work evaluates the efficacy of various promoters (Ca, Ba, Mn, Mg, and K) on Ni/ZrO2 catalysts for CO2 ATR, linking promoter properties to catalytic performance and deactivation resistance. The oxidative atmosphere fundamentally alters promoter function. Barium emerged as the optimal promoter, delivering the highest syngas selectivity (H-2/CO ratio) and superior stability. Its strong basicity maximized CO2 activation for dry reforming while effectively suppressing the H-2-consuming reverse water-gas shift reaction. Furthermore, Ba enhanced structural stability, mitigating sintering under oxidative conditions. Calcium followed a similar, albeit slightly less effective, mechanism. Manganese demonstrated high CO2 conversion driven by its exceptional oxygen storage capacity, which optimally managed the exothermic heat and O-2 distribution, preventing Ni oxidation. Magnesium improved sintering resistance; its weaker basicity limited its effectiveness in the ATR environment. Potassium proved profoundly unsuitable, acting as a potent catalyst poison by promoting total combustion reactions and accelerating sintering through the formation of low-melting-point compounds. The performance hierarchy of Ni-Ca/ZrO2 > Ni-Ba/ZrO2 > Ni-Mn/ZrO2 > Ni-Mg/ZrO2 > Ni-K/ZrO2 underscores that in ATR, strong basicity is the primary descriptor for high H-2 selectivity and stability, while redox properties are key for managing the complex oxidative environment. This study provides critical insights for designing robust catalysts for efficient CO2 valorization via autothermal reforming. [GRAPHICS]