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

Authors: 
Shekhar, M., Purdue University
Akatay, M. C., Purdue University
Pazmino, J., Purdue University
Stach, E. A., Purdue University
Ribeiro, F. H., Purdue University
Delgass, W. N., Purdue University
Zemlyanov, D., Purdue University
Williams, W. D., Purdue University
Mane, A., Argonne National Laboratory


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 300oC and under the WGS reaction mixture consisted of 7% CO, 2% H2O, 37% H2, 9% CO2 at 250oC 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 250oC 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).