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CO Adsorption on Au/TiO2 Catalysts: Observations, Quantification, and Explanation of a Broad-Band Infrared Signal

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journal contribution
posted on 20.10.2017, 00:00 by Camilah D. Powell, Arthur W. Daigh, Meagan N. Pollock, Bert D. Chandler, Christopher J. Pursell
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.