Abstract
The cerium and/or zirconium-doped Cu/ZSM-5 catalysts (CuCexZr1−xOy/ZSM-5) were prepared by ion exchange and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction by hydrogen (H2-TPR). Activities of the catalysts obtained on the selective catalytic reduction (SCR) of nitric oxide (NO) by ammonia were measured using temperature programmed reactions. Among all the catalysts tested, the CuCe0.75Zr0.25Oy/ZSM-5 catalyst presented the highest catalytic activity for the removal of NO, corresponding to the broadest active window of 175–468 °C. The cerium and zirconium addition enhanced the activity of catalysts, and the cerium-rich catalysts exhibited more excellent SCR activities as compared to the zirconium-rich catalysts. XRD and TEM results indicated that zirconium additions improved the copper dispersion and prevented copper crystallization. According to XPS and H2-TPR analysis, copper species were enriched on the ZSM-5 grain surfaces, and part of the copper ions were incorporated into the zirconium and/or cerium lattice. The strong interaction between copper species and cerium/zirconium improved the redox abilities of catalysts. Furthermore, the introduction of zirconium abates N2O formation in the tested temperature range.
Highlights
Metal-based ZSM-5 catalyst has received considerable attention due to its excellent performance in the low-temperature selective catalytic reduction (SCR) reaction [1,2,3,4]
When transition metal is introduced in ZSM-5, the catalytic performance can be enhanced through different types of active species, including isolated ions on the exchange sites within the ZSM-5 structure, metal oxide clusters, and metal oxide particles in the appearance of ZSM-5 [5,6]
Among all the relevant catalysts studied, Cu/ZSM-5 is of particular interest because it exhibits excellent SCR activity in nitric oxide (NO) abatement [7,8]
Summary
Metal-based ZSM-5 catalyst has received considerable attention due to its excellent performance in the low-temperature selective catalytic reduction (SCR) reaction [1,2,3,4]. Among all the relevant catalysts studied, Cu/ZSM-5 is of particular interest because it exhibits excellent SCR activity in NO abatement [7,8]. A major drawback of cerium lies in its poor thermal and hydrothermal stability, especially under a practical diesel exhaust atmosphere [11,13].
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