CO Oxidation on PdO(101) during Temperature-Programmed Reaction Spectroscopy: Role of Oxygen Vacancies

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• 作者：Feng Zhang ; Li Pan ; Tao Li ; John T. Diulus ; Aravind Asthagiri ; Jason F. Weaver
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：December 11, 2014
• 年：2014
• 卷：118
• 期：49
• 页码：28647-28661
• 全文大小：517K
• ISSN：1932-7455

文摘

We investigated the oxidation of CO on PdO(101) using temperature-programmed reaction spectroscopy (TPRS), reflection absorption infrared spectroscopy (RAIRS), and density functional theory (DFT). We find that about 71% of the CO molecules adsorbed in a saturated layer on PdO(101) transform to CO₂ during TPRS, with the CO₂ desorbing in two main features centered at 330 and 520 K. RAIRS shows that CO molecules initially adsorb in an atop configuration on coordinatively unsaturated (cus) Pd sites of PdO(101) located next to O_cus atoms, yielding a RAIRS peak at 2135 cm^鈥?, and that the oxidation of these species produces the CO₂ TPRS peak at 330 K. Concurrent with reaction, a large fraction of CO molecules migrates to atop-Pd_cus sites located next to O_cus atom vacancies (O_v) that are created during reaction, as evidenced by the appearance of a RAIRS peak centered at 鈭?085 cm^鈥?. Our RAIRS measurements demonstrate that oxidation of the CO-Pd_cus/O_v species is responsible for the CO₂ TPRS peak at 520 K, and further show that oxygen atoms from the subsurface readily fill O_v sites as CO molecules vacate the Pd_cus/O_v sites above about 400 K. DFT calculations show that a strong enhancement in binding (鈭?0 kJ/mol) is responsible for the rapid migration of CO molecules from Pd_cus/O_cus sites to Pd_cus/O_v sites as the PdO(101) surface is reduced at low temperature. DFT also predicts that both CO species can access facile pathways for oxidation on PdO(101) via reaction with O_cus atoms, wherein the apparent reaction barriers are nearly identical in each pathway.