Water-gas shift activity of Au and Cu nanoparticles supported on molybdenum oxides

The water-gas shift (WGS, CO + H2O -> H-2 + CO2) reaction was studied on a series of gold/molybdena and copper/molybdena surfaces. Films of MoO2 were grown by exposing a Mo(110) substrate to NO2 at 1000 K. Then, Au and Cu nanoparticles were deposited on the oxide surfaces and their WGS activity was measured in a reaction cell (P-CO = 20 Torr; P-H2O = 10 Torr; T=575-650 K). Although bulk metallic Au is inactive as a catalyst for the WGS and worthless in this respect when compared to bulk metallic Cu, Au nanoparticles supported on MoO2 are a little bit better catalysts than Cu nanoparticles. The WGS activity of the Au and Cu nanoparticles supported on MoO2 is five to eight times larger than that of Cu(100). The apparent activation energies are 7.2 kcal/mol for Au/MoO2, 7.8 kcal/mol for Cu/MoO2, and 15.2 kcal/mol for Cu(100). The Cu/MoO2 surfaces have a catalytic activity comparable to that of Cu/CeO2(111) surfaces and superior to that of Cu/ZnO(000 (1) over bar) surfaces. Post-reaction surface characterization indicates that the admetals in Au/MoO2 and Cu/MoO2 remain in a metallic state, while there is a minor MoO2 -> MoO3 transformation. Formate- and/or carbonate-like species are present on the surface of the catalysts. DFT calculations indicate that the oxide support in Au/MoO2 and Cu/MoO2 is directly involved in the WGS process. (C) 2007 Elsevier B.V. All rights reserved.