Thermochemistry and micro-kinetic analysis of methanol synthesis on ZnO (0001)

Andrew J. Medford, Jens Sehested, Jan Rossmeisl, Ib Chorkendorff, Felix Studt, Jens K. Nørskov, Poul Georg Moses
Year of publication: 
Journal of Catalysis

In this work, we examine the thermochemistry of methanol synthesis intermediates using density func- tional 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 function- als 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 meth- anol 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.