(654f) Ambient Pressure PES Study of Al2O3 Supported Catalysts for Water Gas Shift Reaction

Alumina (Al₂O₃) supported Pt/TiO₂ catalysts for water gas shift (WGS) reaction were analyzed in situ under 0.5 mbar pressure using ambient pressure synchrotron-based Photoemission Spectroscopy (PES). High-resolution core-level spectra were obtained both under reducing atmosphere of H₂ at 300^oC and under the WGS reaction mixture consisted of 7% CO, 2% H₂O, 37% H₂, 9% CO₂ at 250^oC at total pressure of 0.5mbar. To obtain depth profile, the photon energy of the exciting radiation was varied as to have the kinetic energy of photoelectrons ranging from 120eV to 420eV. Oxidation state of metals under different atmospheres and change of the composition as a function of depth were investigated.

A reduced state of titania was identified under both environments on 3.6 wt% Pt/Al₂O₃ sample promoted with 10 wt% TiO₂. Reduced titania was supposed to distribute around and under the Pt nanoparticles under H2 whereas under WGS reaction mixture the reduced titania state was most likely on the boundary around Pt nanoparticles. The depth profiling allowed us to suppose agglomeration of TiO₂. No diffusion of Pt into the support was observed and Pt was not oxidized under these conditions.  Oxidized states of Fe are found on 0.5 wt% Pt/Al₂O₃ sample promoted with 11 wt% Fe. The surface of the support is covered uniformly with the promoter and agglomeration is not as widespread as compared to the titania promoted sample. The WGS rate of the titania promoted sample is 1.3x10^-2 and that of Fe promoted sample is 4.5x10^-2 mole H₂ mole Pt^-1 s^-1 at 250^oC under our standard conditions, a promotion of a factor of 17 and 60, respectively when compared with the un-promoted Pt catalyst.  Based on the findings, models describing the structure of catalysts were developed and compared to images obtained by High-Resolution Transmission Electron Microscopy (HR-TEM).