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Over 90 % of all chemical manufacture uses a solid catalyst. Related workthus responds to major societal demand. This study is of water-gas shift onplatinum for hydrogen production. The close-packed Pt(111) surface catalysesthis process.  Many chemical reactions involve bond-dissociation. This is also true forreactions at solid surfaces, in which the dissociation step is often limitingbut facilitated in comparison to gas phase reaction channels. Sincebond-breaking is poorly described by Hartree-Fock and DFT methods, this workadopts Quantum Monte Carlo (QMC) methodology. QMC is a stochastic approach tosolving the Schr\"odinger equation recently came of age for heterogeneoussystems involving solids.  The present work considers co-adsorption of water and carbon monoxide onPt(111). The water is partially dissociated while its oxygen atom binds to COlosing a hydrogen atom. This concerted step is rate-limiting. The resultingadsorbed formate species then decomposes to readily eliminated carbon dioxideand the clean-fuel product is H$_2$.  The Transition-State geometry can be optimized using molecular Quantum MonteCarlo force constants, on the basis of our earlier work using the CASINOsoftware.  Our embedded active site approach is used. This allows a high-levelconfiguration interaction (CI) wave-function to be used, expanded inplane-waves and embedded in the metal lattice exposing its close-packed face.The resulting periodic function is used to guide the Quantum Monte Carlocalculation.  Results are given here on mechanism and QMC activation barrier for wateraddition to CO pre-adsorbed on Pt(111) of 17 +/- 0.2 c.f. apparent measuredvalue of 17.05 kcal/mol. They are encouraging for investigating similar orcomplex catalytic systems.

Quantum Monte Carlo method for metal catalysis: case study of hydrogen production on Pt(111)