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

The water–gas shift (WGS, CO + H2O → H2 + CO2) reaction was studied on a series of gold/molybdena and copper/molybdena surfaces. Films of MoO2 were grown by exposing a Mo(1 1 0) 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 (PCO = 20 Torr; PH2O=10 TorrPH2O=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(1 0 0). 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(1 0 0). The Cu/MoO2 surfaces have a catalytic activity comparable to that of Cu/CeO2(1 1 1) surfaces and superior to that of Cu/ZnO(0 0 0 1¯) 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.

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