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Highlights: [•] Zirconia introduction favors copper dispersion and inhibits copper crystallization. [•] Zirconia addition is beneficial to enriching copper species on the ZSM-5 surface. [•] The interaction between copper and zirconium enhances the lattice oxygen and site reducibility. [•] The Cu-Zr/ZSM-5 presents a wide activity window within the range of diesel exhaust temperatures. [ABSTRACT FROM AUTHOR]

Abstract: Manganese–zirconium catalysts loaded on ZSM-5 (Si/Al=25) were prepared using an ion-exchange method and investigated for the selective catalytic reduction of NO, with the aim of studying the effects of zirconium doping on the performance of Mn-based ZSM-5 catalysts. A series of characterization techniques, namely N2-sorption, X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy (TEM), temperature-programmed reduction by hydrogen, and X-ray photoelectron spectroscopy (XPS), were used to characterize these samples. TEM and XRD results showed that the addition of zirconium increased the manganese dispersion and prevented manganese crystallization. XPS results demonstrated that the introduction of zirconium enhanced the manganese species enrichment on the ZSM-5 grain surfaces. After zirconium addition, some of the manganese ions were incorporated into the zirconia lattice. The strong interaction between Mn and Zr contributed to the formation of Zr3+ ions or oxygen vacancies around the Zr4+ ions, which enhanced the redox abilities of the Mn–Zr/ZSM-5 catalysts. The temperature range for efficient NO conversion was lowered after zirconium doping. The MnZr3/ZSM-5 (Mn 3.2wt.% and Zr 8.6wt.%) sample exhibited NO x conversions (>90%) over a wide temperature range (230–415°C) and markedly superior to that of Mn/ZSM-5 (296–425°C). Moreover, the formation of N2O was suppressed at low temperatures due to the presence of zirconium in the catalysts. [Copyright &y& Elsevier]

The purpose of the present study is to better understand the reaction kinetics of diesel exhaust soot during oxidation process. A thermogravimetric analyzer was used to oxidize real diesel exhaust soot generated from a Euro VI diesel engine under non-isothermal conditions. The Friedman-Reich-Levi method and the Sestak-Berggren model were used to determine the oxidation kinetics. Raman spectroscopy and high-resolution transmission electron microscopy were employed to follow the changes of the soot structure during oxidation. The activation energy gradually increased with increasing conversion level during soot oxidation. The oxidation process of diesel exhaust soot could be described as three-step kinetics, and the calculated conversions fitted the experimental results very well. The kinetic predictions of diesel soot oxidation that were obtained using the proposed kinetic models were more accurate and precise than those with the common first-order model. The structural order increased as oxidation progressed, which was responsible for the increased activation energy. The structural ordering was principally caused by the preferential oxidation of the disordered fraction in the diesel soot, especially for the amorphous carbon, which was oxidized in the initial stage of the oxidation reaction. [Display omitted] • The oxidation reaction kinetics of diesel exhaust soot were studied. • The activation energy of soot gradually increases with conversion during oxidation. • The oxidation process of diesel soot can be described as three-step kinetics. • The developed kinetic models can reflect the soot oxidation process accurately. • The structural ordering of diesel soot causes the increase in activation energy. [ABSTRACT FROM AUTHOR]

Copper–cerium–zirconium catalysts loaded on TiO 2 prepared by a wet impregnation method were investigated for NH 3 -selective catalytic reduction of NO x , aiming to study the effects of the Ce/Zr molar ratio on the performance of Cu–Ce–Zr/TiO 2 catalysts. The Cu–Ce 0.25 –Zr 0.75 /TiO 2 sample exhibited nearly 100% NO x conversion over a wide temperature range (165–450 °C), which is strikingly superior to that of Cu/TiO 2 (210–389 °C) within the range of exhaust temperatures of diesel engines. The factors that govern the activity enhancement were extensively investigated by using a series of characterization techniques, namely X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction by hydrogen (H 2 -TPR). The results showed that the addition of zirconium and/or cerium refined the copper dispersion, prevented copper crystallization and partially incorporated the copper ions into the zirconia (ceira) lattice, which led to enhance the redox abilities of Cu–Ce–Zr/TiO 2 catalysts. [ABSTRACT FROM AUTHOR]