Effect of noble metals in the decomposition of nitrous oxide over Fe-ferrierites
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Catalysis Letters, Vol. 113, Nos. 3–4, February 2007 ( 2007) DOI: 10.1007/s10562-007-9016-x
Effect of noble metals in the decomposition of nitrous oxide over Fe-ferrierites Zdeneˇk Sobalı´ k,* Kamil Jı´ sˇ a, Dalibor Kaucky´, Alena Vondrova´, Zdenˇka Tvaru˚zˇkova´, and Jana Nova´kova´, J. Heyrovsky´ Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Dolejsˇkova 3, 182 23 Prague 8, Czech Republic
Received 5 November 2006; accepted 21 December 2006
The decomposition of nitrous oxide was studied over Fe-ferrierite, Me-ferrierites and Fe/Me-ferrierites (Me: Pt, Rh and Ru). Flow as well as batch experiments were carried out and showed a synergy between Fe and Me ions. Ions of noble metals in Fe-ferrierite increased the catalytic activity in the sequence Pt < Rh @ Ru. Addition of NO substantially decreased the decomposition of N2O over Rh/ferrierite and Ru/ferrierite, but not over bimetallic ferrierites. NOx species created during the decomposition of nitrous oxide alone as well as with addition of NO, and employment of nitrous oxide labeled with 18O allowed us to assume a changing decomposition mechanism in the presence of Me ions in Fe-ferrierites. KEY WORDS: Fe-, Pt-, Rh- and Ru-ferrierites; synergy effects in Fe/Me-ferrierites; N2O decomposition.
1. Introduction Fe-ferrierite exhibits high activity in the decomposition of nitrous oxide, low deactivation and high oxygen resistance [1–10]. The presence of NO and NO2 even increases the activity [5,9]. In contrast, the reactivity decreases in the presence of moisture [10] and thus the decomposition must proceed above 400 C. Noble metals alone [11–14] or supported [15–18] are also known to efficiently decompose nitrous oxide, but the reaction is inhibited by nitric oxide, oxygen and water [15,18]. Pieterse et al. [10] successfully reduced this drawback using bimetallic zeolite – Fe/Co-mordenite and Fe/Ru-ferrierite. The synergy between metallic and bimetallic systems in Fe/Ru-ferrierite has been tentatively ascribed to a change in the effect of NO [10]. We have studied the decomposition of nitrous oxide over Fe-ferrierite with various iron loading values [3–9]. It appeared that iron located in cationic positions, most probably in b-sites, serves as an active center for the N2O decomposition [3]. Consequently, Fe-ferrireites containing less than 1 wt% of iron (Fe/Al of about 0.06, most b-sites occupied) exhibit the highest activity related to the Fe content. Decomposition of 18O labeled nitrous oxide showed that the recombination of oxygen atoms from N2O proceeds with the participation of zeolite oxygens, as neither the isotopomers 18O2 nor 18O16O were solely formed [7,9]. The analysis of surface species desorbed after the decomposition of nitrous oxide and nitrous oxide + nitric oxide allowed us to assume that NOx species are active intermediates in the N2O *To whom correspondence should be addressed. E-mail: [email protected]
decomposition. They play the role of oxygen scavengers and of oxygen carrier through the zeolite lattice [9
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