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The Remarkable Enhancement of CO‐Pretreated CuOMn 2 O 3 /γ‐Al 2 O 3 Supported Catalyst for the Reduction of NO with CO: The Formation of Surface Synergetic Oxygen Vacancy
Author(s) -
Li Dan,
Yu Qiang,
Li ShanShan,
Wan HaiQin,
Liu LianJun,
Qi Lei,
Liu Bin,
Gao Fei,
Dong Lin,
Chen Yi
Publication year - 2011
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201002786
Subject(s) - catalysis , x ray photoelectron spectroscopy , manganese , octahedron , raman spectroscopy , copper , oxygen , metal , vacancy defect , chemistry , inorganic chemistry , oxide , crystallography , materials science , crystal structure , biochemistry , physics , organic chemistry , optics , nuclear magnetic resonance
NO reduction by CO was investigated over CuO/γ‐Al 2 O 3 , Mn 2 O 3 /γ‐Al 2 O 3 , and CuOMn 2 O 3 /γ‐Al 2 O 3 model catalysts before and after CO pretreatment at 300 °C. The CO‐pretreated CuOMn 2 O 3 /γ‐Al 2 O 3 catalyst exhibited higher catalytic activity than did the other catalysts. Based on X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), UV/Vis diffuse reflectance spectroscopy (DRS), Raman, and H 2 ‐temperature‐programmed reduction (TPR) results, as well as our previous studies, the possible interaction model between dispersed copper and manganese oxide species as well as γ‐Al 2 O 3 surface has been proposed. In this model, Cu and Mn ions occupied the octahedral vacant sites of γ‐Al 2 O 3 , with the capping oxygen on top of the metal ions to keep the charge conservation. For the fresh CuO/γ‐Al 2 O 3 and Mn 2 O 3 /γ‐Al 2 O 3 catalysts, the ‐Cu‐O‐Cu‐ and ‐Mn‐O‐Mn‐ species were formed on the surface of γ‐Al 2 O 3 , respectively; but for the fresh CuOMn 2 O 3 /γ‐Al 2 O 3 catalyst, ‐Cu‐O‐Mn‐ species existed on the surface of γ‐Al 2 O 3 . After CO pretreatment, ‐Cu‐□‐Cu‐ and ‐Mn‐□‐Mn‐ (□ represents surface oxygen vacancy (SOV)) species would be formed in CO‐pretreated CuO/γ‐Al 2 O 3 and CO‐pretreated Mn 2 O 3 /γ‐Al 2 O 3 catalysts, respectively; whereas ‐Cu‐□‐Mn‐ species existed in CO‐pretreated CuOMn 2 O 3 /γ‐Al 2 O 3 . Herein, a new concept, surface synergetic oxygen vacancy (SSOV), which describes the oxygen vacancy formed between the individual Mn and Cu ions, is proposed for CO‐pretreated CuO‐Mn 2 O 3 /γ‐Al 2 O 3 catalyst. In addition, the role of SSOV has also been approached by NO temperature‐programmed desorption (TPD) and in situ FTIR experiments. The FTIR results of competitive adsorption between NO and CO on all the CO‐pretreated CuO/γ‐Al 2 O 3 , Mn 2 O 3 /γ‐Al 2 O 3 , and CuOMn 2 O 3 /γ‐Al 2 O 3 samples demonstrated that NO molecules mainly were adsorbed on Mn 2+ and CO mainly on Cu + sites. The current study suggests that the properties of the SSOVs in CO‐pretreated CuOMn 2 O 3 /γ‐Al 2 O 3 catalyst were significantly different to SOVs formed in CO‐pretreated CuO/γ‐Al 2 O 3 and Mn 2 O 3 /γ‐Al 2 O 3 catalysts, and the SSOVs played an important role in NO reduction by CO.