1 Center for Atomic-scale Materials Design, Center, Technical University of Denmark2 Department of Physics, Technical University of Denmark3 Experimental Surface and Nanomaterials Physics, Department of Physics, Technical University of Denmark4 Solar Energy Programme, Risø National Laboratory for Sustainable Energy, Technical University of Denmark5 Haldor Topsoe AS6 SLAC National Accelerator Laboratory7 Stanford University8 Haldor Topsoe AS
In this work, we examine the thermochemistry of methanol synthesis intermediates using density functional theory (DFT) and analyze the methanol synthesis reaction network using a steady-state micro-kinetic model. The energetics for methanol synthesis over Zn-terminated ZnO (0001) are obtained from DFT calculations using the RPBE and BEEF-vdW functionals. The energies obtained from the two functionals are compared and it is determined that the BEEF-vdW functional is more appropriate for the reaction. The BEEF-vdW energetics are used to construct surface phase diagrams as a function of CO, H2O, and H2 chemical potentials. The computed binding energies along with activation barriers from literature are used as inputs for a mean-field micro-kinetic model for methanol synthesis including the CO and CO2 hydrogenation routes and the water–gas shift reaction. The kinetic model is used to investigate the methanol synthesis rate as a function of temperature and pressure. The results show qualitative agreement with experiment and yield information on the optimal working conditions of ZnO catalysts.