Quantum Monte Carlo Approach for Determining the Activation Barrier of Water Addition to Carbon Monoxide Adsorbed on Pt(111) within 1 kJ/mol

Quantum Monte Carlo (QMC) methods offer ab initio calculations of remarkable accuracy for reaction activation barriers (to 1 kJ/mol or 0.01 eV), even at solid surfaces. Chemical reactions generally involve bond dissociation that is poorly described by Hartree-Fock and density functional theory (DFT) methods. However, such processes are often the key to rate-limiting reaction steps at solid surfaces. In this work, a novel QMC methodology is demonstrated as a solution. Carbon monoxide (CO) on platinum reacts with water, first giving the addition products. QMC methods are used here to investigate addition at close-packed Pt(111). The CO is preadsorbed on Pt(111). First, an approaching water molecule is only partially dissociated. At the same time, its oxygen atom binds to CO giving an adsorbed formate moiety (COOH) and Pt-H. This concerted addition is rate-limiting. The QMC activation barrier (in kJ/mol) is 71.0 ± 0.7, and its apparent measured value is 71.4. This showcases QMC as a method to investigate related catalytic systems.