Short communicationHigh-silica nanoflower hierarchical Fe-MFI with excellent catalytic performance for N2O decomposition
Graphical abstract
Introduction
Nitrous oxide (N2O) is not only one of the major sources of nitrogen oxides (NOx) depleting the ozone layer in the stratosphere, but also a strong greenhouse gas with a global warming potential approximately 300 times higher than that of CO2 [1]. In recent years, N2O decomposition to harmless N2 and O2 is considered as an ideal abatement and is popularly studied [2]. Amongst, Fe/ZSM-5 is a relatively cheap and effective catalyst in N2O decomposition [3], [4], [5]. In addition, the enhancement by the presence of NO is observed in the Fe/ZSM-5 catalyst, which is an advantageous peculiar property for the treatment of the real exhausted gases [6]. However, the conventional microporous ZSM-5 catalyst suffers from diffusion limitation during the ion exchange process and the Si-OH(Al) exchange sites are not fully utilized, which will limit the catalytic activity [7]. Recently, ZSM-5 with hierarchical structure has been developed to improve the mass diffusion and shows the potential to improve the catalytic performance [8], [9], [10]. To the best of our knowledge, several methods have been reported to prepare the micro-mesoporous hybrid ZSM-5, including post treatments such as dealumination/desilication, solf/hard-template synthesis method with multifunctional structure-directing agents (SDAs) [11], [12], [13], [14]. Post treatment as an effective and cheap method, has its shortages, such as poor reproducibility, difficult controllability and multi preparation steps. Therefore, in this work, high-silica ZSM-5 zeolite with hierarchical pore structure was developed by a facile synthesis method [15] and its activity in the N2O decomposition was determined. It is found that the catalytic performance of the micro-mesoporous hybrid Fe/ZSM-5 with nanoflower morphology is significantly better than that of conventional microporous ZSM-5 in N2O decomposition.
Section snippets
Preparation of hierarchical Fe-ZSM-5
A hierarchical zeolite with nanoflower structure was synthesized by a solvothermal method and the detailed chemical synthesis is carried out as follows: 10.367 g of tetra(n-butyl)phosphonium hydroxide (TBPOH, 40% by weight, SigmaAldrich), 0.031 g/0.052 g/0.087 g of sodium hydroxide, 0.102 g/0.204 g/0.408 g of aluminum sulfate (Sigma-Aldrich), 2.79 g of H2O and 3.00 g of powdered SiO2 was mixed to form a solution with different compositions 60SiO2: 0.3Al2(SO4)O3: 18TBPOH: 0.9NaOH: 600H2O/60SiO2: 0.6Al2(SO
Results and discussion
The textural and morphologic property is investigated by the X-ray diffraction (XRD) pattern, N2 adsorption-desorption isotherms, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). As shown in Fig. 1(A), the XRD patterns of parent supports show the typical diffraction peaks of ZSM-5 structure, which indicates the successful synthesis of ZSM-5 zeolites [16]. After iron exchanged, the diffraction peaks are maintained, implying the well preservation of zeolite structure
Conclusions
In summary, a facile one-pot hydrothermal method has been developed to obtain nanoflower ZSM-5 zeolites with micro-mesoporous hybrid structure. The resulting Fe/ZSM-5 samples exhibited high crystallinity, high BET surface area and total pore volume and adjustable Si/Al ratio. The special hierarchical structure of the ZSM-5 is constructed with the micropores and ca. 3.6–5.7 nm mesopore, which lead to the fully utilization of exchange sites and the significant increase of active loading though the
Acknowledgement
This work is financially supported by the National Natural Science Foundation for Young Scholar (No. 21307144).
Notes and references
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