In this work, we show that if the mere procedure of impregnation of oxide supports with chloroauric acid, which is well-known to lead to large gold particles, is followed by a step of washing with ammonia, small gold particles (3-4 nm) can be obtained after a treatment of calcination at 300 degrees C on any type of oxide supports (alumina, titania, silica). Moreover, gold leaching is very limited during the washing step, and a large range of gold loadings (0.7-3.5 wt %) can be achieved. Elemental analysis, Raman spectroscopy, and temperature programmed desorption under argon show that this ammonia posttreatment results in the removal of chloride ligands from the coordination sphere of Au(III) precursor and their replacement by ammine ligands, leading to an ammino-hydroxo or an ammino-hydroxo-aquo gold complex and not to gold hydroxide. The Au/TiO(2) catalysts prepared with this modified procedure of impregnation are almost as active as those prepared by deposition-precipitation with urea in the CO oxidation reaction performed at room temperature.

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Reducing of nitrogen oxides (NO x ) in a lean exhaust gases has become one of the most important environmental concerns. Among the different active phases studied for NO x reduction reaction, silver-based catalysts supported over alumina show good performances using, as reducing agents, either hydrocarbons or oxygenated compounds. Nevertheless, a good understanding of the mechanism reaction has not been reached yet. This comprehension requires a better characterisation of the silverbased catalysts system. In our study, Ag/Al 2 O 3 catalysts showed high efficiency in NO x reduction using ethanol as reducing agent. The conversion plots, in steady state conditions for the different samples Ag/Al 2 O 3 (0.8-3.5% Ag wt), show a great dependance of the activity with the metal loading. The optimal silver loading has been established around 2 wt.% Increasing the silver loading, the temperature of maximal NO x conversion shifted toward the lower temperatures. According to the literature, a reduced and an oxide phase of silver have been observed by UV-Vis spectroscopy. The ratio between the two phases is changing with the silver loading. However, temperature programmed reduction (TPR) measurements reveal the presence of two types of oxide phases. TPR reveal the coexistence of a silver oxide phase (Ag 2 O), according to a production of water in the course of the reaction, and a non-oxygenated phase attributed to isolated Ag ? cation. Thus, an original way using TPR measurements has been developed to differentiate the various oxidized phases. The aim of this characterisation is to correlate the catalyst's activity with the observed silver phases, in order to understand the nature of phase active for NO x reduction at low temperatures.

Gasification tar, causing various process equipment problems, is an undesirable product during biomass gasification therefore catalysts for its decomposition are needed. Toluene as a model tar compound was tested on steam reforming reaction using ceria-zirconia based Ni and Co catalysts.