Water-Gas Shift on Pd/alpha-MnO2 and Pt/alpha-MnO2

Low temperature water-gas shift (WGS) catalysts, Pd nanoparticles supported on alpha-MnO2 nanorods termed Pd/alpha-MnO2 and Pt nanoparticles supported on alpha-MnO2 nanorods termed Pt/alpha-MnO2 were synthesized by introducing Pd or Pt precursor to well-prepared alpha-MnO2 nanorods through precipitation deposition with a following annealing at 300 A degrees C. They are quite active for WGS in the temperature range of 140-350 A degrees C. Activation energies for WGS on Pd/alpha-MnO2 and Pt/alpha-MnO2 are 45.3 and 56.4 kJ/mol respectively, comparable to precious metal supported on CeO2 and TiO2 for WGS. Surface chemistries of the two catalysts during WGS were tracked with ambient pressure X-ray photoelectron spectroscopy. Different from the preservation of the surface and bulk phase of other oxide support such as CeO2, TiO2 in CeO2- or TiO2-based WGS catalysts, both surface and bulk of alpha-MnO2 nanorods of Pd/alpha-MnO2 and Pt/alpha-MnO2 are transited to MnO during WGS. In-situ studies identified oxygen vacancies of the formed MnO support during WGS and the metallic state of Pd and Pt nanoparticles supported on the nonstoichiometric MnO.