Effect of Sodium in Ferrierite on Selective Catalytic Reduction of NO by Acetylene
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Effect of Sodium in Ferrierite on Selective Catalytic Reduction of NO by Acetylene Hui Pan Æ Xinping Wang Æ Na Xing Æ Zhiguan Liu
Received: 31 December 2007 / Accepted: 20 May 2008 / Published online: 10 June 2008 Ó Springer Science+Business Media, LLC 2008
Abstract Influence of sodium in ferrierite (HFER) zeolite on selective catalytic reduction of NO by acetylene (C2H2-SCR) was investigated. NOx-TPD and FT-IR indicated that small amount of sodium exchanged into the proton-form zeolite with an exchange level of about 11.8% is beneficial for the title reaction by accelerating active nitrate species formation on catalyst surface from NO2 and by suppressing the reductant combustion. Nevertheless, no further improved catalytic performance in C2H2-SCR could be observed by a larger amount of sodium exchanged into HFER due to some inactive nitrate species formed on the zeolite. Instead, activity of the zeolite for C2H2-SCR was drastically reduced, since the capacity of the zeolite for catalyzing NO oxidation and accelerating active NO+ species formation was remarkably depressed. Keywords Sodium FER Nitrosonium ions Nitrate Acetylene Selective catalytic NO reduction
1 Introduction Selective catalytic reduction of NO with hydrocarbons (HC-SCR) in excess oxygen has received much attention recently because of its potential application to mobile leanburn engines [1–4]. Since the HC-SCR was first studied over Cu-ZSM-5 catalysts by Iwamoto et al. [5], large number of investigations were reported over the zeolite
H. Pan X. Wang (&) N. Xing Z. Liu State Key Laboratory of Fine Chemicals, Dalian University of Technology, 288#, Linggong Road 2, Dalian 116024, China e-mail: [email protected]
based catalysts. Na and H form zeolites were usually used as precursors for preparation of the catalysts, and the activity of the zeolite for HC-SCR was reported to be strongly affected by the counter ions (H+ or Na+) in zeolites. For instance, it was reported that Ag-NaZSM-5 catalyst is more active than Ag-HZSM-5 for the selective catalytic reduction of NO by methane (CH4-SCR) at 450 °C [6], and that Fe-ZSM-5 catalyst prepared from NaZSM-5 is far more active than that prepared from NH4ZSM-5 for selective catalytic reduction of NO by urea [7]. Similarly, high activity for the selective catalytic reduction of NO by propene (C3H6-SCR) on Ce-NaZSM-5 [8, 9] and for CH4-SCR on Pt-Co-NaFER washcoated cordierite monolith [10] was obtained. Whereas, Bro¨nsted acids have been suggested to be essential for HC-SCR over many catalytic systems (e.g. ZSM-5 modified by Pd, Ga, In, Ce and Ag) [11–18]. The authors found that Bro¨nsted acids contributed to the aimed reaction in different steps. Also, Stakheev et al. have pointed out that protons in ZSM-5 are quite important for C3H6-SCR. They reported that exchange of partial protons by sodium with a level of 32% resulted in a nearly complete disappearance of the activity of the zeolite for oxidation of NO to NO2, and a significant decrease of the activity for C3H6-SCR [19]. On the other hand,
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