This review article summarizes the contents of the keynote lecture with the same tittle presented at the 7 th edition of the International Conference on Environmental Catalysis hold in Lyon (France) in September 2012. Different aspects of the ceria-catalyzed Diesel soot combustion reactions have been critically discussed, such as the high catalytic activity of ceria for Diesel soot combustion in comparison to some other potential catalysts, the potential ceria-catalyzed Diesel soot combustion mechanisms (the so-called NO 2 -assisted mechanism and the active oxygen mechanism) and the effect of ceria doping with suitable cations like those of Pr, La or Zr. Ceria must be doped in order to enhance thermal stability, but ceria doping also changes different physicochemical and catalytic properties of ceria. Zr-doping, for instance, has a double role on ceria as soot combustion catalyst: enhances ceria oxidation capacity of the adsorbed NOx species (positive effect) but stabilizes NO 2 on surface (negative effect). The surface properties of a ceria catalyst are usually more important than those of bulk: high surface area/small crystal size usually has a positive effect on the catalyst performance and, in mixed oxides, the surface composition also plays a role. The optimal dopant loading depends on the foreign cation being, for instance, around 5-10%, 20-30% and 50 mole % for La 3+ , Zr 4+ , and Pr 3+ / 4+ , respectively.Keywords: DPF regeneration; soot; ceria; doped-ceria; Diesel engine contamination. 2This review article summarizes the contents of the keynote lecture with the same tittle presented at the 7 th edition of the International Conference on Environmental Catalysis hold in Lyon (France) in September 2012. 1.-The problem.Soot particles are formed as undesired by-products in combustion process, being one of the main pollutants emitted by Diesel engines together with NOx, CO and unburned hydrocarbons [1]. Typical gas exhaust composition of a Diesel car, which is summarized in Table 1, is 30-80 ppm hydrocarbons, 200-1500 ppm CO, 300-1650 ppm NO (~ 0 ppm NO 2 ), 5-18% O 2 , > 2% H 2 O and > 2% CO 2 .Soot particles consist of a carbon nucleus with some inorganic material and adsorbed hydrocarbons, SO x , and water [2]. Figure 1 shows TEM images of a real soot sample. The single particles of few nanometers present an amorphous core surrounded by a graphitic shell, and such single particles agglomerate in larger entities with size typically in the range 0.1-10 µm [3].Several adverse effects on health have been attributed to soot. A fraction of these particles (the so-called PM-10, with size smaller than 10 m) can penetrate the respiratory tract and are deposited on lungs increasing cancer risk, asthma and bronchitis. The adsorbed hydrocarbons are mutagenic substances and SO x in contact with water form strong acid compounds.Diesel particle traps with different designs can be used for soot removal from gas streams, wall-flow monoliths being the most popular [3,4]. Figure 2 shows a commercial SiC Diesel Part...

A new nanocomposite catalyst consisting of high-loading cobalt oxide (CoO) on nitrogen-doped reduced graphene oxide (rGO) for oxygen reduction reaction (ORR) was prepared in this work. Its high activity for the ORR in alkaline electrolyte was determined using the rotating disk electrode technique, and further confirmed in real alkaline membrane fuel cells. A combination of physicochemical characterization (e.g., X-ray absorption and X-ray photoelectron spectra) and density functional theory (DFT) calculation suggests that cobalt(II) cations in the composite catalyst may coordinate with the pyridinic nitrogen atoms doped into graphene planes, most likely the active species for the ORR. Especially, the DFT calculations indicate that a stable rGO(N)–Co(II)–O–Co(II)–rGO(N) structure can be formed in the nitrogen-doped graphene catalyst. Kinetic parameter analysis shows a high selectivity of four-electron reduction on the composite catalyst during the ORR with an average electron transfer number of 3.75. A synergistic effect between the rGO(N) and CoO may exist, yielding a much higher catalytic activity on the CoO/rGO(N) catalyst, compared to either rGO(N) or CoO controls. The novel synthesis procedure utilizing rGO(N) to further couple Co(II) yields a high loading of Co species (24.7 wt %). Thus, a relatively thinner cathode in fuel cell can accommodate more active Co species and facilitate O2 transfer. Due to the high intrinsic activity and efficient mass transport, the CoO–rGO(N) ORR catalyst achieved approaching performance to state-of-the-art Pt/C cathodes in anion-exchange-membrane alkaline fuel cells.

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Model CuO/Ce 0.8 X 0.2 O δ catalysts (with X = Ce, Zr, La, Pr, or Nd) have been prepared in order to obtain CuO/ceria materials with different chemical features and have been characterized by X-ray diffraction, Raman spectroscopy, N 2 adsorption, and H 2 temperature-programmed reduction. CO-PROX experiments have been performed in a fixed-bed reactor and in an operando DRIFTS cell coupled to a mass spectrometer. The CO oxidation rate over CuO/ceria catalysts correlates with the formation of the Cu + −CO carbonyl above a critical temperature (90 °C for the experimental conditions in this study) because copper−carbonyl formation is the rate-limiting step. Above this temperature, CO oxidation capacity depends on the redox properties of the catalyst. However, decomposition of adsorbed intermediates is the slowest step below this threshold temperature. The hydroxyl groups on the catalyst surface play a key role in determining the nature of the carbon-based intermediates formed upon CO chemisorption and oxidation. Hydroxyls favor the formation of bicarbonates with respect to carbonates, and catalysts forming more bicarbonates produce faster CO oxidation rates than those which favor carbonates.