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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]

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]