CO Adsorption on Au/TiO2 Catalysts: Observations, Quantification, and Explanation of a Broad-Band Infrared Signal
2017
Powell, Camilah D. | Daigh, Arthur W. | Pollock, Meagan N. | Chandler, Bert D. | Pursell, Christopher J.
The adsorption of CO on Au/TiO₂ catalysts was examined at room temperature using FTIR transmission spectroscopy. Adsorption was observed as (i) a sharp peak at ∼2100 cm–¹ due to CO molecular vibration (the Au–CO peak), and (ii) a broad-band infrared (BB-IR) signal. The Au–CO peak and BB-IR signal are correlated and quantitatively related to the amount of CO adsorbed on the Au nanoparticles. For comparison purposes, we also examined CO adsorption on Au/Al₂O₃ catalysts. When supported on this nonreducible support, CO adsorption on Au showed only the Au–CO peak; the BB-IR signal was absent. This allowed us to determine that the BB-IR signal observed for CO adsorption on the Au/TiO₂ catalyst is associated with the reducibility of the support. Comparison of the two catalysts also enabled us to determine that the BB-IR signal is due to a decrease in transmission through the powdered catalysts when CO adsorbs on Au/TiO₂. Consistent with previously published studies, we propose that this BB-IR signal is related to the reversible, partial reduction of the TiO₂ at the Au–TiO₂ interface. This reduction leads to an increase in surface disorder or roughening of TiO₂ particles that produces a decrease in IR transmission through the catalyst (i.e. an increase in IR scattering). These results suggest an efficient CO–Au–TiO₂ adsorbate-induced electronic metal–support interaction (EMSI) that may play an important role in understanding CO reactions on Au/TiO₂ catalysts.
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