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Synthesis and evaluation of mesopore structured ZSM-5 and a CuZSM-5 catalyst for NH3-SCR reaction: studies of simulated exhaust and engine bench testing

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Abstract

A modified ZSM-5 zeolite (denoted as ZSM-5-M), which was synthesized using tetrapropylammonium hydroxide (TPAOH) and cetyltrimethylammonium bromide (CTAB) as dual templates, and the commercial ZSM-5 zeolite (denoted as ZSM-5-C), have been used to prepare the corresponding CuZSM-5 (M & C) catalysts containing 3 wt% Cu by ion exchange method. Compared to CuZSM-5-C catalyst, the CuZSM-5-M catalyst demonstrated remarkably higher catalytic activity at low temperatures (<450 °C) for selective catalytic reduction of NOx with NH3 both in the simulated exhaust and engine bench testing. The modified synthesis by the dual template with the product aged for a long time at room temperature, leads to the formation of the ZSM-5-M zeolite with much higher specific surface area (608 m2 g−1) and higher total pore volume (0.8880 cm3 g−1) due to the presence of more mesoporous pores. The X-ray diffraction results showed that ZSM-5-M maintained its typical MFI structure, while its crystallinity (84.1%) was lower than that of the ZSM-5-C zeolite. The characterization results by H2 temperature-programmed reduction and X-ray photoelectron spectra revealed that the higher redox properties of isolated Cu2+ ions combined with the high-dispersion CuO crystallites and Cu+ ions are likely the main cause for the excellent low-temperature activity of the CuZSM-5-M catalysts. The isolated active Cu2+ species and high-dispersion CuO crystallites had a stronger interaction with other atoms in CuZSM-5-M catalysts. The results from thermogravimetric analysis, temperature-programmed desorption of ammonia and in situ diffuse reflectance infrared Fourier transform spectroscopy demonstrated that ZSM-5-M is a strong Brønsted acid site and the CuZSM-5-M catalyst had a relatively higher exchange rate of Cu2+ and Cu+ ions and more Lewis acidic sites, giving it a high NH3 adsorption capacity. The strong Brønsted acid site might be another cause that results in the higher NH3-SCR performance of the CuZSM-5-M catalyst.

Graphical abstract: Synthesis and evaluation of mesopore structured ZSM-5 and a CuZSM-5 catalyst for NH3-SCR reaction: studies of simulated exhaust and engine bench testing

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Publication details

The article was received on 10 Aug 2016, accepted on 03 Oct 2016 and first published on 06 Oct 2016


Article type: Paper
DOI: 10.1039/C6RA20237C
Citation: RSC Adv., 2016,6, 102570-102581
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    Synthesis and evaluation of mesopore structured ZSM-5 and a CuZSM-5 catalyst for NH3-SCR reaction: studies of simulated exhaust and engine bench testing

    Z. Li, X. Chen, J. Li, X. Ren, S. Liu, J. Gao, J. W. Schwank, T. Zhang, W. Su and H. Chang, RSC Adv., 2016, 6, 102570
    DOI: 10.1039/C6RA20237C

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