Methane Pyrolysis Using a Multiphase Molten Metal Reactor

Methane pyrolysis is a unique approach toward generating hydrogen and valuable carbon products, with the added advantage of low to near-zero CO2 emissions. Currently, the most popular method for hydrogen production is steam methane reforming, which generates more than 10 kg of CO2 for every 1 kg of hydrogen. By comparison, methane pyrolysis produces hydrogen and solid carbon with no COx biproduct. Methane pyrolysis on a conventional solid catalyst exhibits low activation energy, but the carbon coproduct cannot be separated and rapidly poisons the surface (coking). On the other hand, molten liquid metal catalysts have been shown to have the advantage of separatable carbon, but their high activation energy limits the rate of the reaction and potential for economic industrialization. In this work, methane pyrolysis was shown using a multiphase molten metal reactor where both liquid and solid metal alloy catalysts were in equilibrium. Catalytic measurements using a Sn–Ni melt showed that operating the reactor in the two-phase region of the Sn–Ni phase diagram decreased the apparent activation energy from 355 kJ/mol in the liquid-only melt to 158 kJ/mol, all while maintaining the ability to separate and recover graphitic carbon

Methane Pyrolysis Using a Multiphase Molten Metal Reactor

Methane pyrolysis is a unique approach toward generating hydrogen and valuable carbon products, with the added advantage of low to near-zero CO2 emissions. Currently, the most popular method for hydrogen production is steam methane reforming, which generates more than 10 kg of CO2 for every 1 kg of hydrogen. By comparison, methane pyrolysis produces hydrogen and solid carbon with no COx biproduct. Methane pyrolysis on a conventional solid catalyst exhibits low activation energy, but the carbon coproduct cannot be separated and rapidly poisons the surface (coking). On the other hand, molten liquid metal catalysts have been shown to have the advantage of separatable carbon, but their high activation energy limits the rate of the reaction and potential for economic industrialization. In this work, methane pyrolysis was shown using a multiphase molten metal reactor where both liquid and solid metal alloy catalysts were in equilibrium. Catalytic measurements using a Sn–Ni melt showed that operating the reactor in the two-phase region of the Sn–Ni phase diagram decreased the apparent activation energy from 355 kJ/mol in the liquid-only melt to 158 kJ/mol, all while maintaining the ability to separate and recover graphitic carbon

Influence of LaNiO₃ Shape on Its Solid-Phase Crystallization into Coke-Free Reforming Catalysts

Shape-controlled LaNiO₃ nanoparticles were prepared by modified hydrothermal and precipitation routes resulting in cubes, spheres, and rods. The solid-phase crystallization of LaNiO₃ into its active catalyst form, Ni/La₂O₃, was found to be highly dependent on the shape and structure of the parent nanoparticle. Factors such as the crystallization pathway and Ni²⁺-ion depletion are considered as key factors influencing the final material. Catalysts derived from LaNiO₃ spheres and rods were found to be free of carbon accumulation after 100 h of reforming, while those derived from cubes showed excessive carbon accumulation and signs of sintering. All three catalysts are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), temperature-programmed reduction (TPR), and thermogravimetric analyses (TGA). The presence of defects, particularly stacking faults within the perovskite, may impact the reduction pathway and subsequent catalytic properties. Stable and active catalysts can therefore be designed and tuned by controlling the shape and structure of perovskite precursors

Nanoparticle Silver Catalysts That Show Enhanced Activity for Carbon Dioxide Electrolysis

Electrochemical conversion of CO₂ has been proposed both as a way to reduce CO₂ emissions and as a source of renewable fuels and chemicals, but conversion rates need improvement before the process will be practical. In this article, we show that the rate of CO₂ conversion per unit surface area is about 10 times higher on 5 nm silver nanoparticles than on bulk silver even though measurements on single crystal catalysts show much smaller variations in rate. The enhancement disappears on 1 nm particles. We attribute this effect to a volcano effect associated with changes of the binding energy of key intermediates as the particle size decreases. These results demonstrate that nanoparticle catalysts have unique properties for CO₂ conversion