Hydrogen is an indispensable commodity chemical. Steam reforming produces 50 million tons of H2 annually with 300 million tons of CO2 byproduct. The goal of our research is to use the reaction CH4 = C + 2H2 to produce hydrogen without CO2. When performed in gas phase this reaction is inefficient and we need to find a catalyst. Traditional supported catalysts are rapidly poisoned by the carbon formed in the reaction. To avoid carbon poisoning, methane is bubbled through a bed of molten metal catalyst. Catalysis takes place at the bubble-liquid interface and the carbon formed by the reaction segregates at the surface of the melt and can be skimmed off. The use of a molten metal catalyst may be helpful for other reactions plagued by coking. This talk will present the molten metal catalysts discovered so far. They are molten binary alloys that consist of a metal that melts below 1000 °C (e.g. Ag, Pb, Sn, Ga, In, Bi, Sn, Te) in which we dissolve a metal that is known to be an active catalyst (e.g. Ni, Pt, Pd, Cu). A metal dissolved in a melt does not have the same catalytic properties as the solid metal. One of the goals of our research is to determine the difference in activity and the extent of the synergy between the components of the melt. Simulations by ab initio, constant temperature molecular dynamics provide unexpected insights. We have found that the “active component” is atomically dispersed in the melt. A Pt2 or a Pt8 cluster inserted in a molten metal “solvent” dissociates in a few picosecond producing negative ions. Electrons from the “solvent” metal (e.g. Sn) are instantly transferred to the antibonding orbitals of Pt cluster, destroying the Pt-Pt bonds and causing a “Coulomb explosion”. Carbon has some solubility in the melt and the simulations show that the C atoms are also negatively charged. For the economics of the process it is important to produce clean carbon. So far, we have not succeeded in doing this and the carbon is contaminated with the metals used in the melt.

Hydrogen production without CO2: Experiments and computations

256th National Meeting (2018)

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