Nowadays, there is pressing demand for sustainable energy sources, or clean and 'green' fuel and hydrogen is a perfect candidate.This work shows how to use Quantum Monte Carlo calculations to take (user-guided) information summarising chemistry of heterogeneous catalysis from a generic Jastrow factor, that allows electron correlation to be included in the density. This, in turn, gives accurate values of properties, in particular the activation barrier for the water addition step in the catalysed water-gas shift reaction, to produce hydrogen. This step follows adsorption of CO on Pt(111), pure or layered onto the close-packed face of aluminium.The CO co-ordinates to a hollow site defined by three Pt atoms and, new to this work, an Al-atom co-ordinates the H-atom from dissociating an in-coming water molecule.This work is dedicated to the memory of Sir John Meurig Thomas 15.12.1932-13.11.2020, a great mentor in heterogeneous catalysis.The author still recalls JMT's courses with admiration and his lecture notes are a real treasure.