The Nature of Active Sites of Co/Al 2 O 3 for the Selective Catalytic Reduction of NO with C 2 H 4
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The Nature of Active Sites of Co/Al2O3 for the Selective Catalytic Reduction of NO with C2H4 Xiaomei Chen Æ Aimin Zhu Æ Chuan Shi
Received: 22 July 2009 / Accepted: 25 August 2009 / Published online: 11 September 2009 Ó Springer Science+Business Media, LLC 2009
Abstract The effects of Co loading and calcination temperatures on the catalytic activity of Co/Al2O3 for selective catalytic reduction (SCR) of NO with ethylene in excess oxygen were investigated. Co/Al2O3 showed high and low activities when calcined at high (800 °C) and low (350 °C) temperatures, respectively. The formation and dispersion of cobalt species for catalysts calcined at 350 and 800 °C as well as for Al2O3 were studied by XRD, UV–vis and FTIR spectra. Combined with DRIFTS results of ad-species and reaction experiments, it allowed us to correlate the catalytic activity with active sites of Co/Al2O3, and the catalytic functions of active cobalt species and support were clarified. Co3O4 species contributed to the oxidation of NO to various nitrates and of C2H4 to reactive formate species, even in the absence of O2, whereas the side reaction of ethylene combustion occurred simultaneously when excess oxygen was present. Tetrahedral Co2? ions in CoAl2O4, which acted as the active sites, were responsible for the reaction between formate and nitrate species to form organic nitro compound. Keywords NO selective catalytic reduction Co/Al2O3 Active sites Ethylene DRIFTS
X. Chen A. Zhu C. Shi Laboratory of Plasma Physical Chemistry, Dalian University of Technology, 116024 Dalian, People’s Republic of China C. Shi (&) State Key Laboratory of Fine Chemicals, Dalian University of Technology, 116012 Dalian, People’s Republic of China e-mail: [email protected]
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1 Introduction Selective catalytic reduction of nitrogen oxides (NOx) with hydrocarbons (HC-SCR) is a promising method to remove NOx from various exhausts [1, 2]. Many studies on HC-SCR are related to the metal-containing zeolitic catalysts [3–5] and metal oxides [6–8]. Among them, the metal supported Al2O3 catalysts are of great importance as promising SCR catalysts due to their superior hydrothermal stability and sulphur resistance, such as Cu/Al2O3 [7], Co/Al2O3 [8], Ag/Al2O3 [9] and Ga/Al2O3 [10]. Since Hamada et al. [11] reported that alumina-supported cobalt shows high activity for NO reduction with C3H6 as reductant in the presence of H2O and SO2, extensive research has been devoted to investigate the activity of Co/Al2O3 and the mechanism for HC-SCR reactions [8, 12, 13]. Generally, the catalytic activity of cobalt supported alumina catalysts depends on the type of support, preparation method, metal loading and calcination temperatures [8, 14, 15], major challenge to understand the activity of Co/Al2O3 catalysts lies in the heterogeneous distribution of cobalt species. Indeed, the state of Co species is a key issue which closely associates with the activity and mechanism of Co/Al2O3. In other words, elucidation of the active sites is essential for relating the structures of Co
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