Short time-to-solution Quantum Monte Carlo for catalysed hydrogen synthesis. Tools give CO hydrolysis activation barriers to 1kJ/mol on Pt(111)

Abstract

Hydrogen synthesis is a clean, sustainable alternative to fossil fuel \cite{gals}. It has come of age: prototyping various aspects of hydrogen power are hot topics. In 9 out of 10 reactions, a solid catalyst is used. Here hydrogen production (via water-gas shift) is studied. Adsorbed reactants are optimidsed on model Pt(111). Focus is on partial O-H bond dissociation, when CO is co-adsorbed with water on this plane. hydrogen is the product. Many chemical reactions involve bond-dissociation. This process is often the key to rate-limiting reaction steps at solid surfaces. Bond-breaking is poorly described by Hartree-Fock and DFT methods, our embedded active site approach is used. We showcase Quantum Monte Carlo (QMC) methodology using the ground-state Slater Determinant of a simple four primitive-cell layer model, oriented to expose Pt (111), to initialise the QMC. This stochastic approach solves the Schr{\"o}dinger equation. It recently came of age for heterogeneous systems involving solids. During hydrolysis of carbon monoxide, initial O-H bond stretch is rate-limiting. Its dissociation energy is offset by surface Pt-H bond formation. The reactive formate (H-O-C=O) species formed by initial hydrolysis of CO, also interacting with a vicinal Pt. The products are hydrogen (CO$_2$ by-product is mineralised. A H-atom dissociates from the formate, another is desorbed from Pt(111). This yields pure hydrogen. Single-determinant work with a novel averaging procedure is compared to a high-level configuration interaction (CI) wave-function. Activation barriers are given to 0.86kJ/mol (c.f. 0.7 of the CI benchmark). Active sites embedded in metal lattice (111) faces. These trial wave-functions guide QMC.