Operando X-ray absorption spectroscopy study of supported Pt catalysts during NO reduction by hydrocarbons

摘要

To investigate the support effect on the hydrocarbon-NO-O2 reaction in automotive three-way catalytic reactions, operando X-ray absorption near edge structure (XANES) experiments were performed for reactions of C3H6 (or C3H8)-NO-O2 over Pt supported catalysts under reducing conditions.γ-Al2O3, ZrO2, CeO2-ZrO2 and La2O3 were used as the support oxides in this study. After oxidation pre-treatment, the oxidation state of the supported Pt was monitored by in situ Pt L3-edge XANES spectra while the temperature in the reaction mixture was ramped up and the catalytic reaction was followed by measuring the concentrations of C3H6 or C3H8, NO and O2. The operando experimental results were analyzed in terms of the catalytic reaction start-up temperature (20% HC conversion temperature) and the 50% Pt reduction temperature. A V-shape correlation was found between these two temperatures showing that an appropriate Pt reduction temperature should exist to lower the catalytic reaction start-up temperature. This result suggests that the creation of active metallic Pt sites together with the self-poisoning effect of adsorbed carbonaceous species on metallic Pt should determine the catalytic reaction start-up behavior of supported Pt catalysts. Besides the suitable Pt reduction temperature, the oxygen reactivity in the support oxide is also important for lowering the catalytic start-up temperature. The control of the Pt-support interactions to provide suitable Pt reducibility and also oxygen reactivity in oxide support are both important to achieve a lower catalytic reaction start-up temperature.