Selective catalytic reduction of NO on single site FeSiBEA zeolite catalyst: Influence of the C1 and C2 reducing agents on the catalytic properties

https://doi.org/10.1016/j.apcatb.2012.04.026Get rights and content

Abstract

FeSiBEA zeolite with 0.8 Fe wt% is prepared in acidic condition (pH 2.5) by a two-step postsynthesis method which allows to incorporate iron into framework of zeolite as mononuclear distorted tetrahedral Fe(III) species, as evidenced by XRD, diffuse reflectance UV–vis and X-ray absorption spectroscopy. The single site FeSiBEA catalyst with isolated and framework Fe centres is active in SCR of NO process with C2 (ethanol and ethylene) reducing agents, with selectivity towards N2 exceeding 90% in the broad temperature range from 573 to 723 K for maximum NO conversion about 50 and 30% at 573 K for ethanol and ethylene respectively. In contrast, this catalyst is much less active with C1 (methanol and methane) reducing agents, with maximum selectivity towards N2 not exceeding 65% with methanol and 10% with methane for maximum NO conversion of 10 and 23% respectively. The low activity in CH4-SCR of NO on Fe0.8SiBEA catalyst containing only isolated mononuclear distorted tetrahedral Fe(III) species in the framework zeolite could be explained by high energy of Csingle bondH bond, which should be broken to activate methane molecule.

Highlights

▸ Iron is incorporated in framework of zeolite as mononuclear tetrahedral Fe(III). ▸ The single site FeSiBEA catalyst is active in SCR of NO with ethanol and ethylene. ▸ The selectivity towards N2 exceeding 90% in the broad temperature range. ▸ FeSiBEA shows inferior activity with methanol and methane. ▸ The selectivity towards N2 is inferior 65% with methanol and 10% with methane.

Introduction

Transition metal containing zeolites are active in many catalytic reactions including oxidative dehydrogenation of alkanes [1], [2], [3], selective catalytic reduction (SCR) of NO by reducing agents [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21] and direct N2O decomposition [22], [23]. Iron zeolites are known to be active in several reactions, such as N2O decomposition [24], [25], [26], [27], selective catalytic reduction of NOx and N2O [5], [28] and selective oxidation of different substrates [29], [30], [31], [32]. Although the big number of papers were reported on NO removal since a pioneer works of Iwamoto [33] and Held [34], only in some of their a mechanism of SCR of NO process were deeply discussed and no universal description of this process on zeolites was reported up till now. The main reasons of this were the complexity of various potential active centres in zeolite material and diversity of organic compounds chosen as the NO reducing agents.

The first problem can be greatly reduced if well-defined catalysts with isolated metal centre could be prepared. The current methods of dispersing transition metals in zeolites such as classical impregnation or ion exchange are not efficient method to obtain well defined isolated centre because the presence of iron impurities in commercial zeolites, as we have earlier reported [35]. EPR and Mössbauer spectroscopies have been evidenced that in commercial BEA zeolite iron impurities are present as tetrahedral Fe(III) and octahedral Fe(III) species. Iron impurities present in commercial BEA zeolite are active in the selective catalytic reduction (SCR) of NO by ethanol, with NO conversion higher than 37% and with selectivity towards N2 higher than 90% in the temperature range 575–775 K. The high activity of commercial BEA suggests that Fe(III) impurities are present in tetrahedral and/or octahedral environments, possibly close to lattice Al, which make them active in the SCR of NO by ethanol. However, this is only an assumption and it should be confirmed. So to prepare well defined Fe single site zeolite catalyst without Fe impurities and Al ions we have developed a two-step postsynthesis method which consists first of creating vacant T-atom sites by removal of Fe impurities and Al ions from framework and extra framework position of BEA zeolite by treatment with nitric acid and then, in the second step, impregnating the resulting pure SiBEA material with Fe precursor [36] to incorporate Fe ions into framework position. As we have recently reported [13], [37], this postsynthesis method allows, for low Fe content (<2 wt%), to incorporate iron into framework of SiBEA zeolite as isolated distorted tetrahedral Fe(III), without formation of FeOx oligomers or iron oxide.

In the presented work, the single site FeSiBEA zeolite with 0.8 Fe wt% was prepared containing isolated and framework Fe centres and used as catalyst in SCR of NO with C1 (methanol and methane) and C2 (ethanol and ethylene) reducing agents. The choice of alcohols has both application and fundamental purposes, because the lower alcohols are often used as a fuels or additives in different combustion processes and as the reducing agents in SCR of NO process.

The objective of this work was to investigate the influence of the C1 and C2 reducing agents on the catalytic properties of FeSiBEA zeolite and to show the role of mononuclear iron species on SCR of NO process.

Section snippets

Catalyst preparation

FeSiBEA catalyst with 0.8 Fe wt% was prepared by the two-step postsynthesis method reported earlier [13], [36], [37]. To obtain the FeSiBEA, 2 g of siliceous beta (SiBEA) zeolite (Si/Al > 1300), obtained by treatment of a tetraethyl ammonium BEA zeolite (Si/Al = 11) provided by RIPP (China) in a 13 mol L−1 HNO3 (supplier: VWR Prolabo, AnalaR Normapur 68%) solution (at 353 K for 4 h, were stirred for 24 h at 298 K in aqueous solution containing 1 × 10−3 mol L−1 of Fe(NO3)3 × 9·H2O (supplier: Merck, for analysis,

X-ray diffraction

Fig. 1 shows the XRD patterns of AlBEA, SiBEA and Fe0.8SiBEA which are all of typical BEA zeolite. This indicates that crystallinity of BEA zeolite is preserved after dealumination and incorporation of Fe ions in zeolite structure. The decrease of the d302 spacing related to the narrow main diffraction peak near 22–23° from 3.942 (AlBEA) (with 2θ of 22.55°) to 3.912 Å (SiBEA) (with 2θ of 22.71°) upon dealumination indicates contraction of the matrix as a result of removal Al [36], [40]. In

Conclusions

FeSiBEA zeolite with 0.8 Fe wt% prepared in acidic conditions (pH 2.5) by a two-step postsynthesis method allows to control the incorporation of iron into framework of BEA zeolite evidenced by XRD.

For such low Fe content, iron is incorporated into the zeolite as mononuclear framework tetrahedral Fe(III) species as evidenced by DR UV–vis and EXAFS spectroscopies.

The single site FeSiBEA catalyst with isolated and framework Fe centres are active in SCR of NO process with C2 (ethanol and ethylene)

References (59)

  • M.D. Uddin et al.

    Journal of Catalysis

    (1994)
  • P.B. Venuto

    Microporous Materials

    (1994)
  • H.Y. Chen et al.

    Catalysis Today

    (1998)
  • G. Centi et al.

    Catalysis Today

    (1999)
  • R. Burch et al.

    Applied Catalysis B

    (1994)
  • Y. Li et al.

    Applied Catalysis B

    (1993)
  • M. Haneda et al.

    Journal of Catalysis

    (2000)
  • M. Haneda et al.

    Applied Catalysis B

    (2001)
  • S. Dzwigaj et al.

    Catalysis Today

    (2007)
  • T. Tabata et al.

    Catalysis Today

    (1996)
  • H. Ohtsuka et al.

    Catalysis Today

    (1998)
  • T. Tabata et al.

    Microporous Mesoporous Materials

    (1998)
  • H.H. Chen et al.

    Applied Catalysis B

    (2004)
  • Y. Traa et al.

    Microporous Mesoporous Materials

    (1999)
  • G. Bagnasco et al.

    Journal of Catalysis

    (2004)
  • J. Janas et al.

    Applied Catalysis B

    (2007)
  • F. Kapteijn et al.

    Journal of Catalysis

    (1997)
  • E.M. El-Malki et al.

    Journal of Catalysis

    (2000)
  • F. Kapteijn et al.

    Applied Catalysis B

    (1996)
  • J.A.Z. Pieterse et al.

    Applied Catalysis B

    (2004)
  • G.D. Pirngruber et al.

    Catalysis Today

    (2005)
  • M. Kogel et al.

    Journal of Catalysis

    (1999)
  • J. Jia et al.

    Journal of Catalysis

    (2004)
  • A. Ribera et al.

    Journal of Catalysis

    (2000)
  • Q. Kan et al.

    Journal of Molecular Catalysis

    (1992)
  • S. Dzwigaj et al.

    Applied Catalysis B

    (2009)
  • J. Janas et al.

    Applied Catalysis B

    (2009)
  • M.A. Camblor et al.

    Zeolites

    (1993)
  • S. Bordiga et al.

    Journal of Catalysis

    (1996)
  • Cited by (14)

    • Vanadium incorporation from aqueous NH<inf>4</inf>VO<inf>3</inf> solution into siliceous Beta zeolite determined by NMR with formation of V-single site zeolite catalysts for application in SCR of NO

      2020, Applied Catalysis A: General
      Citation Excerpt :

      The two-step post-synthesis method allowed incorporating vanadium in SiBeta zeolite mainly as isolated pseudo-tetrahedral V species for low vanadium content (lower than 2 V wt %) without formation of VOx oligomers, as shown earlier by XRD, DR UV–vis and FTIR [15]. As shown earlier [16–22], the two-step post-synthesis method also allowed incorporating copper, iron and cobalt cations in the framework of the SiBeta zeolite thus obtaining Cu-, Fe- and Co-single site Beta zeolites active in selective catalytic reduction of NO into N2. Such catalytic materials are of highly relevant importance considering that the problematic of exhaust gas cleaning is very important from many decades and has thus been the subject of many reviewers [23–29].

    • Remarkable activity of Ag/Al<inf>2</inf>O<inf>3</inf>/cordierite catalysts in SCR of NO with ethanol and butanol

      2013, Applied Catalysis B: Environmental
      Citation Excerpt :

      According to [6,14,42], in SCR of NOx with ethanol organo-nitrogen intermediate complexes (R-ONO, R-NO2, where R: ·C2H5), formed during the reaction of enolic and nitrate species, are transformed into the key intermediate NCO species. During the decomposition of organo-nitrogen compounds formed of butanol molecule (R-ONO, R-NO2, where R: ·C4H9), NCO species can be formed together with hydrocarbon fragments which have CC bonds (the importance of CC bonds for reductant of NO in the SCR-reaction was shown in [49,52]). Then these hydrocarbon fragments either may be oxidized to CO2 and H2O or form oxygenates which are reactive in the SCR of NOx.

    View all citing articles on Scopus
    View full text