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The effect of Pd doping on the NOx removal efficiency and NH 3 selectivity was studied over lean NOx trap LaCo 1- x Pd x O 3 -Ba/Al 2 O 3 -type catalysts. Two catalysts were prepared by the sequential impregnation of 15 wt% of LaCo 1- x Pd x O 3 -type perovskites and 20 wt% of barium over alumina. The results of X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, temperature programmed techniques, UV–vis diffuse reflection absorption spectroscopy, and X-ray photoelectron spectroscopy demonstrated that perovskite and barium grains uniformly distribution over the alumina surface. Cobalt partial substitution by palladium changed the chemical coordination environment, thus leading to the redox properties of perovskites getting different. Moreover, the LaCoO 3 –Ba/Al 2 O 3 catalyst exhibited a high reduction on NOx by H 2 between 450 and 550 °C. Whereas Pd-doped LaCo 0·9 Pd 0·1 O 3 –Ba/Al 2 O 3 catalyst decreased the best activity interval around 100 °C, as well as improved the NH 3 selectivity. The NOx reduction conversion of the LaCo 0·9 Pd 0·1 O 3 –Ba/Al 2 O 3 catalyst increased significantly from 72.9% to around 100% at H 2 /NO ratio = 1, and the production of NH 3 was increased from 20.1% to 58.6% at H 2 /NO ratio = 3. • Novel perovskite-based catalysts were synthesized for excellent textural properties. • Pd changes the chemical environment of the cobalt metal ions and enhances the redox properties of LaCoO 3. • Pd enhances H 2 dissociation thus offering more H ions to promote the NH 3 generation. [ABSTRACT FROM AUTHOR]

• The GDI soot was harvested from a China VI passenger vehicle operated over the WLTC. • The Physicochemical properties of GDI soot were investigated. • The physicochemical properties of the SB4 are similar to those of the GDI soot. • The SB4 and GDI soot have almost the same oxidation reactivity. • The SB4 can serve as a surrogate for GDI soot for oxidation investigations. The purpose of the present study is to understand the physicochemical properties of the GDI soot and determine a GDI soot surrogate for the oxidation investigations. The high-resolution transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy and thermogravimetric analyzer were used to characterize the soot properties, including the morphology, nanostructure, chemical composition, carbon chemical state and oxidation reactivity. The GDI soot sample was harvested from the gasoline particulate filter equipped on a modern China VI passenger vehicle operated over the Worldwide harmonized Light-duty Test Cycle. The obtained GDI soot comprises large numbers of near-spherical primary particles that cluster together to form aggregates with a mean gyration radius of 123.79 nm, and the mean diameter of primary particles is 27.63 nm. The primary particle exhibits a typical core–shell structure, and the mean values of fringe length, separation distance and tortuosity are 0.836 nm, 0.362 nm and 1.263, respectively. In addition to the carbon element, the oxygen element is another important component of soot particles, accounting for 6.28% of the total number of atoms. The carbon component is mainly composed of sp2 hybridized graphitic carbon and sp3 hybridized aliphatic carbon, and the ratio of sp2/sp3 is 2.02. Moreover, the apparent activation energy of soot sample is determined to be 141.7 kJ/mol. The Special Black 4 (SB4) was assessed as a potential surrogate for the GDI soot. The comparison of physicochemical properties shows that the SB4 and GDI soot have almost the same fractal dimension, gyration radius, primary particle size, fringe length, separation distance, tortuosity, sp2/sp3 ratio and apparent activation energy. The great similarities in physicochemical properties highlight that the SB4 can serve as a good GDI soot surrogate for the soot oxidation investigations. [ABSTRACT FROM AUTHOR]

• A series of excellent properties NH 3 -SCR catalysts. • The introduction of Ce and Zr can increase SCR activity and anti-thermal aging in NOx abatement. • 6%Ce-2%Zr/Cu-ZSM-5 catalyst has an excellent SCR activity than Cu-ZSM-5 catalyst in the presence of water vapor. The effects of cerium and cerium + zirconium supported over Cu-ZSM-5 on SCR activity and anti-thermal aging performance in NOx abatement have been studied. X-ray diffraction, scanning electron microscopy, UV–vis diffuse reflectance, temperature-programmed technologies, Fourier transform infrared spectroscopy, and in-situ diffuse reflectance infrared Fourier transform spectroscopy were used to characterize the surface properties and transition-state species of the catalysts. The 6 %Ce-2 %Zr/Cu-ZSM-5 catalyst exhibits excellent NOx purification activity under dry and water vapor conditions and the best thermal aging resistance. Copper and zirconium species formed are in the nanometer size range and are well dispersed on the ZSM-5 surface, and cerium was formed with the low crystallinity of CeO 2 as an increase of cerium content. Cerium and zirconium addition improve copper dispersion and the cooperative effect between copper and cerium/zirconium. Zirconium can promote the presence of copper in the form of ionic state rather than oxides, improve copper species dispersion, assist to stabilize the framework of ZSM-5, and prevent copper cations precipitation sintering. There were no obvious correlations between acid site strength and the SCR catalytic activity. The NH 3 -SCR reaction over 6 %Ce-2 %Zr/Cu-ZSM-5 catalyst co-follows the Eley-Rideal and Langmuir-Hinshelwood mechanism. [ABSTRACT FROM AUTHOR]

An excellent textual properties and performance La 0.9 Ce 0.1 Co 0.9 Pd 0.1 O 3 -BaO/Al 2 O 3 catalyst was synthesized. The reaction mechanism of H 2 /NOx over the La 0.9 Ce 0.1 Co 0.9 Pd 0.1 O 3 -BaO/Al 2 O 3 catalyst was investigated by temperature programmed reduction/ desorption/ surface reaction (TPR/D/SR) technologies and in-situ diffuse reflectance Fourier transform (DRIFT) technology. The results show that cerium or palladium species are inserted into the cells of LaCoO 3 , as well as they synergetic promote the redox properties of the La 0.9 Ce 0.1 Co 0.9 Pd 0.1 O 3 -BaO/Al 2 O 3 catalyst. Surface activated nitrates exist over the La 0.9 Ce 0.1 Co 0.9 Pd 0.1 O 3 -BaO/Al 2 O 3 catalyst, with thermal stable increasing in the order: absorbed N 2 O 4 < monodentate nitrates < chelating bidentate nitrates < nitrates unidentate < free ionic nitrates < bulk free ionic nitrates. H 2 preferentially reacted with absorbed N 2 O 4 and monodentate nitrates at low temperatures, due to their high activity. The concentration of generated NH 3 from the redox reaction of H 2 /NOx achieves the maximum value between 350 and 450 °C over the La 0.9 Ce 0.1 Co 0.9 Pd 0.1 O 3 -BaO/Al 2 O 3 catalyst. Compared with the NOx adsorption process at 50 °C, monodentate nitrates and absorbed N 2 O 4 disappeared due to their low thermal stability, chelating bidentate nitrates become stronger, as well as free ionic nitrates converted to bulk free ionic nitrates with higher thermal stability at 350 °C. When H 2 is exposed to NOx species adsorbed on La 0.9 Ce 0.1 Co 0.9 Pd 0.1 O 3 -BaO/Al 2 O 3 , chelating bidentate nitrates and bulk free ionic nitrates are consumed gradually, indicating that although the bulk free ionic nitrates own high stability, it also could be consumed by involving in the H 2 /NOx reaction at 350 °C. The quantitative H 2 /NO reaction experiments confirmed the results of H 2 -TPSR and NSR. It is beneficial to the formation of NH 3 when the H 2 /NO ratio is more than 2.5. Comparing traditional Pt-BaO/Al 2 O 3 catalyst, the La 0.9 Ce 0.1 Co 0.9 Pd 0.1 O 3 -BaO/Al 2 O 3 catalyst exhibit an excellent performance, including considerable NH 3 production property, lower N 2 O selectivity, and the precious metal saving. [Display omitted] • An excellent textual properties and performance La 0.9 Ce 0.1 Co 0.9 Pd 0.1 O 3 -BaO/Al 2 O 3 catalyst was synthesized. • The reduction behavior of the stored NOx over the La 0.9 Ce 0.1 Co 0.9 Pd 0.1 O 3 -BaO/Al 2 O 3 catalyst was researched. • The H 2 /NO reaction process over the La 0.9 Ce 0.1 Co 0.9 Pd 0.1 O 3 -BaO/Al 2 O 3 catalyst was investigated. [ABSTRACT FROM AUTHOR]

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]

The storage and reduction of NOx on a series of Fe-modified hydrotalcite-based lean NOx trap catalysts were assessed, together with the product selectivity. The crystal structures and micromorphologies of these materials were characterized using X-ray diffraction and scanning electron microscopy, while in situ diffuse reflectance Fourier transform infrared spectroscopy was used to evaluate the evolution of transition state species. The introduction of Fe was found to improve the synergistic interaction between the Mg and Fe in the hydrotalcite structure, allowing these catalysts to work efficiently at low temperatures. In addition, both Pt/BaO/MgAlO and Pt/BaO/MgFeO catalysts exhibited better NOx adsorption and reduction performance compared with Pt/BaO/Al 2 O 3. The superior performance of the former two materials was attributed to the enhanced adsorption of NOx in the form of nitrates and nitrites by Fe and Mg and to the ready decomposition of these nitrates at low temperatures. A Pt/BaO/MgFeO catalyst showed excellent low temperature activity and high selectivity for N 2 together with superior sulfur resistance compared with Pt/BaO/Al 2 O 3. [Display omitted] • This study prepared a series of hydrotalcite-derived lean NOx trap catalysts. • The introduction of Fe was found to increase the NOx removal efficiency at low temperature because of improving the synergistic interaction between the Fe and Mg in the hydrotalcite structure. • Pt/BaO/MgFeO has better sulfur resistance than traditional Pt/BaO/Al 2 O 3 catalysts. [ABSTRACT FROM AUTHOR]

Experiments were performed on a CH 4 lean premixed flame to better understand the effect of the oxidation-induced fragmentation of primary particles on soot oxidation reactivity. An aerosol generator was used to homogeneously disperse diesel soot into the flame. Because minimal soot was formed in this flame itself, the information about diesel soot fragmentation was readily obtained. The thermophoretic and probe sampling techniques were used to obtain soot particles at various heights above the burner. The particle size distribution, oxidation reactivity, nanostructure and carbon chemical state of each sample were characterized. The soot reactivity was evaluated in terms of activation energy. The results indicate a higher extent of aggregate fragmentation occurs at moderate soot burnout percentages and that the internal structure in soot is not destroyed during aggregate fragmentation. At higher soot burnout percentages, the internal burning produces more primary particle fragmentation, so that the soot particles exhibit an increase in fringe tortuosity and decreases in fringe length and sp2/sp3 hybridization ratio. These variations in physicochemical properties increase the oxidation reactivity of the soot particles. [ABSTRACT FROM AUTHOR]