Several nanosized catalysts Co3O4-CeO2 with varying compositions were synthesized by a surfactant-template method and further promoted by a small amount of Pd (0.5 wt%). These catalysts exhibit uniform mesoporous structure and high surface area (>100m2g-1). The Co3O4 crystallites in these catalysts are encapsulated by nanosized CeO2 with only a small fraction of Co ions exposing on the surface and strongly interacting with CeO2. Such structure maximizes the interaction between Co3O4 and CeO2 in three dimensions, resulting in unique redox properties. The introduction of Pd prominently enhances both the reduction and oxidation performance of the catalysts, due to hydrogen or oxygen spillover. These catalysts prepared by surfactant-template method exhibit excellent oxidation performance, especially the ones promoted with Pd, which show markedly enhanced CO oxidation activity even at room temperature. Based upon the results of structural properties, redox behaviors and in situ DRIFTS study, two different reaction pathways over Co3O4-CeO2 and Pd/Co3O4-CeO2 are proposed.

The influence of the introduction of Pt and/or Fe on the structures, NOx storage property and sulfur removal performance of Ba/Al2O3 catalyst was studied. The techniques of TG/DTA, XRD, FT-IR, H2-TPR, EXAFS and DRIFTS were employed for the careful characterization of the catalysts. Two types of Ba species are identified, namely a well-spread monolayer of Ba species and a bulk BaAl2O4 phase. The addition of Fe inhibits the Ba dispersion by enhancing the bulk BaAl2O4 formation, thus slightly decreasing the SOx absorption and greatly suppressing the growth of the bulk BaSO4, and its addition also promotes the NOx storage by increasing the mobility of the stored NOx, contributing to the formation of bulk Ba (NO3)2. The introduction of Pt always re-disperses the bulk BaAl2O4 phase via a hydration process, and enhances both the NOx and SOx absorption capacity of the catalyst. Whereas the co-existence of Pt and Fe was detrimental for the NOx storage and sulfur removal as compared with Pt/Ba/Al2O3 catalyst, although it favors the reduction of BaSO4 phase. Based upon the EXAFS, in situ DRIFTS and repeated H2-TPR results, it is found that the interaction between Pt and Ba species is of great importance for NOx storage and sulfur removal. This Pt-Ba interaction not only accelerates the NOx spillover which is a key step during storage, but also facilitates the selective reduction of BaSO4 into H2S, favorable to sulfur removal and catalyst regeneration. The introduction of Fe to the Pt/Ba/Al2O3 catalyst decreases this Pt-Ba interaction by encapsulation of Pt in the matrix of Fe/FeOx lattice after repeated redox cycles, leading to the decrease of NOx storage capacity (NSC) of the catalyst, and making sulfur removal more difficult since Fe selectively catalyzes the reduction of BaSO4 into BaS.

A series of nanostructured Pd-doped mixed oxides MOx-CeO2 (M = Mn, Fe, Co, Ni, Cu), with uniform mesoporous structure and large surface area exceeding 115m2g-1, were synthesized in one step by a surfactant-assisted co-precipitation. Their catalytic performance was investigated using total oxidation of CO and C3H8 as the model reactions. The results show that, a synergism exists between even trace amounts of exposed Pd and 3d-transition metal oxides for CO oxidation, whereas such an effect is absent for C3H8 oxidation. In situ diffuse reflectance infrared spectroscopy (DRIFTS) study reveals that the synergistic essential for CO oxidation should be the interaction-assisted generation of active oxygen species between Pd and MOx, which react readily with CO, forming bidentate carbonate (1587 and 1285cm-1) as intermediates. Moreover, structural characterization results indicate that a solid solution is formed between CeO2 and Mn2O3 or Fe2O3, resulting in the very strong interaction between Pd and MOx, as well as the greatly improved CO oxidation. The light-off temperatures for Pd-doped Mn and Fecontaining catalysts, as compared with the Pd-free catalysts, are decreased by more than 70 and 100℃, respectively. In particular, a CO conversion as high as 80% can be achieved even at room temperature on Pd-doped Mn-containing catalyst. While for C3H8 oxidation, the C-H bond activation, but not the oxygen activation, plays a crucial role. The C-H bond activation ability of the catalysts is largely determined by the d-electron configurations of the M cations. A 'double-peak' phenomenon can be derived with the increase of d-electron number.

The NSR catalyst Pt/K/TiO2-ZrO2 was prepared by successive impregnation. In situ DRIFTS technique was employed to investigate the NOx storage mechanisms. The results show that no adsorbed NOx species were detected over TiO2-ZrO2, while nitrite and nitrate species could be identified simultaneously over K/TiO2-ZrO2. After Pt deposition, only nitrates species, such as free nitrate ions and monodentate or bidentate nitrates, were observed. The main NOx storage route is via the potassium sites (Ⅰ) adjacent to Pt, the potassium sites (Ⅱ) away from Pt trap NOx only after the saturation of potassium sites (Ⅰ).

A mesoporous NSR catalyst Pt/BaCO3-Al2O3 was synthesized by using tri-block copolymer P123 as template. Systematic comparative studies on the structural and catalytic performance between the mesoporous catalyst and the conventional impregnated one were performed. N2 physisorption, XRD, TPD were employed for their structural characterization. In situ DRIFTS, TPR, TEM were used for investigation of the catalytic behaviors for NOx and SOx sorption, as well as desulfation. The results of structural characterization show that mesoporous Pt/BaCO3-Al2O3 exhibits high surface area (261m2g11 after calcination at 600℃), uniform pore size with a diameter of ca. 5 nm and high thermal stability up to 800℃. The Ba-containing species are highly dispersed in three-dimensions and strongly interacted with Al2O3, and all the BaCO3 presents as LT-BaCO3 (BaCO3 with low thermal stability). By contrast, most of the Ba species in the impregnated sample exist predominantly as HT-BaCO3 (BaCO3 with high thermal stability) and are enriched on the surface. As a result, the mesoporous sample possesses great advantages in serving as NSR catalysts, such as enhanced NOx trapping ability, lower sulfation degree, and higher desulfation extent, as compared with the impregnated one. In addition, after NOx and SOx sorption, no bulk phases of barium nitrates and sulfates were observed in the mesoporous catalyst, while they are evidently formed on the impregnated one. In a word, the mesoporous structure is of great significance in achieving high dispersion of barium species and better performance for NOx storage and regeneration of the catalyst.