Water-gas-shift reaction on metal nanoparticles and surfaces

Density functional theory was employed to investigate the water-gas-shift reaction (WGS, CO+H2O -> H-2+CO2) on Au-29 and Cu-29 nanoparticles seen with scanning tunneling microscopy in model Au/CeO2(111) and Cu/CeO2(111) catalysts. Au(100) and Cu(100) surfaces were also included for comparison. According to the calculations of the authors, the WGS on these systems operate via either redox or associative carboxyl mechanism, while the rate-limiting step is the same, water dissociation. The WGS activity decreases in a sequence: Cu-29 > Cu(100)> Au-29 > Au(100), which agrees well with the experimental observations. Both nanoparticles are more active than their parent bulk surfaces. The nanoscale promotion on the WGS activity is associated with the low-coordinated corner and the edge sites as well as the fluxionality of the particles, which makes the nanoparticles more active than the flat surfaces for breaking the O-H bond. In addition, the role of the oxide support during the WGS was addressed by comparing the activity seen in the calculations of the authors for the Au-29 and Cu-29 nanoparticles and activity reported for X/CeO2(111) and X/ZnO(000 < overline > i )(X=Cu or Au) surfaces. (c) 2007 American Institute of Physics.