Activity, stability, and deactivation behavior of supported Au/TiO_2 catalysts in the CO oxidation and preferential CO oxidation reaction at elevated temperatures

摘要

The influence of elevated reaction temperatures on the activity, long-time stability, and deactivation behavior of Au/TiO_2 catalysts for CO oxidation was studied by kinetic and in situ IR measurements in the temperature range 80-180 °C, both in an idealized, H_2-free reaction atmosphere and in a H_2-rich gas mixture. The results are discussed in a molecular picture. Most important for practical applications (PROX reaction), the selectivity for CO oxidation in H_2-rich gas mixtures decreases sharply with increasing temperature, from ～60% at 80 °C to ～15% at 180 °C. The increasing tendency for H_2 oxidation is reflected also by a distinctly lower apparent activation energy for CO oxidation in the presence of H_2 (18 ± 3 kJ mol~(-1)) compared to reaction in a H_2-free reaction mixture (30 ± 3 kJ mol~(-1)). In all cases, carbonate formation is observed and proposed to contribute to the deactivation, but with different extents depending on the reaction conditions.