Adsorption and reaction of formic acid on stoichiometric CeO 2 (111), partially reduced CeO 2– x, and Pt/CeO 2 (111) films prepared on Cu(111) were studied by means of synchrotron radiation photoelectron spectroscopy (SRPES), resonant photoemission spectroscopy (RPES), infrared reflection absorption spectroscopy (IRAS), and temperature-programmed desorption (TPD). On all studied samples, the principal species formed during formic acid adsorption below 160 K were formate and molecular formic acid. In the presence of Pt particles, formate species were predominantly localized on Pt at 100 K, and on ceria at or above 300 K. Below 400 K, molecular formic acid decomposes to formate with partial release of CO 2, CO, hydrogen, and water. Analysis of the TPD fragmentation suggests additional evolution of methane. Above 400 K, desorption of CO 2, CO, hydrogen, and water is observed. This process is controlled by the stoichiometry of ceria and the presence of Pt particles. In particular, desorption of CO 2 is suppressed on CeO 2– x but is enhanced on Pt/CeO 2 . RPES suggests that the reaction of formic acid does not alter the oxidation state of cerium cations on CeO 2 (111). By contrast, we observed significant reoxidation on partially reduced CeO 2– x, between 250 and 400 K, followed by reduction between 400 and 500 K.
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Lykhach et al. (2013) studied this question.
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