Activity, stability and deactivation behavior of Au/CeO2 catalysts in the water gas shift reaction at increased reaction temperature (300°C)

The effect of increasing the reaction temperature to 300 degrees C on the activity, stability and deactivation behavior of a 4.5 wt.% Au/CeO2 catalyst in the water gas shift (WGS) reaction in idealized reformate was studied by kinetic and spectroscopic measurements at 300 degrees C and comparison with previously reported data for reaction at 180 degrees C under similar reaction conditions [A. Karpenko, Y. Denkwitz, V. Plzak, J. Cai, R. Leppelt, B. Schumacher, RJ. Behm, Catal. Lett. 116 (2007) 105]. Different procedures for catalyst pretreatment were used, including annealing at 400 degrees C in oxidative, reductive or inert atmospheres as well as redox processing. The formation/removal of stable adsorbed reaction intermediates and side products (surface carbonates, formates, OHad, COad) was followed by in situ IR spectroscopy (DRIFTS), the presence of differently oxidized surface species (Au-0, Au-0', Au3+, Ce3+) was evaluated by XPS. The reaction characteristics at 300 degrees C generally resemble those at 180 degrees C, including (i) significantly higher reaction rates, (ii) compatable apparent activation energies (44 +/- 1/50 +/- 1 kJ mol(-1) vs. 40 +/- 1 kJ mol(-1) at 180 degrees C), (iii) a correlation between deactivation of the catalyst and the build-up of stable surface carbonates, and (iv) a decrease of the initially significant differences in activity after different pretreatment procedures with reaction time. Different than expected, the tendency for deactivation did not decrease with higher temperature, due to enhanced carbonate decomposition, but increases. (C) 2008 Elsevier B.V. All rights reserved.