Quantum Monte Carlo method describing supported metal catalysis: Ni(111)/alumina decomposing methane as a route to hydrogen

Abstract

Hydrogen production as a clean, sustainable replacement for fossil fuels is gathering pace. Doubling the capacity of Paris-CDG airport has been halted, even with the upcoming Olympic Games, until hydrogen-powered planes can be used. It is thus timely to work on catalytic selective hydrogen production and optimize catalyst structure. Over 90% of all chemical manufacture uses a solid catalyst. This work describes the dissociation of a C–H bond in methane, chemisorbed at Ni(111) that stabilizes the ensuing Ni–H linkage. In a subsequent step, gaseous hydrogen is given off. Many chemical reactions involve bond dissociation. This process is often the key to rate-limiting reaction steps at solid surfaces. Since bond-breaking is poorly described by Hartree–Fock and density functional theory (DFT) methods, quantum Monte Carlo (QMC) methodology is used. Our embedded active site approach demonstrates novel QMC. The rate-limiting reaction step of methane decomposition to hydrogen and carbon is the initial C–H bond stretch. The full dissociation energy is offset by Ni–H bond formation at the surface. Reactive methyl (CH3) radicals also interact with a vicinal Ni. These adsorbed methyl radicals subsequently produce methylene and hydrogen, with one atom dissociated from the methyl radical and the other desorbed from the Ni surface supported on alumina. The QMC activation barrier found is 85.4 ± 1.1 kJ/mol,1 less than 0.5 kJ/mol above DFT benchmark values.2 Thus, QMC is shown to be encouraging for investigating similar catalytic systems.