Showing papers by "Luca Lietti published in 2007"

Fischer–Tropsch synthesis on sulphur poisoned Co/Al2O3 catalyst

Abstract: The effect of sulphur poisoning (in the range 0–2000 ppm) on the characteristics and catalytic performances in the Fischer–Tropsch synthesis (FTS) of a bench-scale alumina supported cobalt catalyst is investigated in this study. It is found that sulphur did not lead to appreciable variations in the catalyst morphological characteristics; however, the catalyst reducibility/hydrogenating capability is significantly modified upon increasing the sulphur loading. The comparison between the catalytic performances of the sulphured samples pointed out that the presence of sulphur remarkably affected the productivity and the selectivity of the reaction. In particular for low S amounts ( These effects have been tentatively associated with different effects of sulphur on the catalyst active sites, i.e. on the sites (or site ensembles) responsible for CO hydrogenation and for the chain growth processes. Finally, the experimental data of CO conversion decay with S-loading were nicely described according to a simple deactivation model which implies a strong effect of sulphur on the catalyst active sites.

High performances of Pt-K/Al2O3 versus Pt-Ba/Al2O3 LNT catalysts in the simultaneous removal of NOx and soot

Abstract: The potentiality of a Pt-K/Al2O3 catalyst in the simultaneous removal of particulate matter (soot) and NO x is investigated in this work by means of Temperature Programmed Oxidation (TPO) experiments and Transient Response Method (TRM), and compared with Pt-Ba/Al2O3. The results point out the higher performances of K-based sample in the soot combustion as compared to the Ba-based catalyst, and similar behaviour in the NO x -storage.

How to control the selectivity in the reduction of NOx with H2 over Pt-Ba/Al2O3 Lean NOx Trap catalysts

Abstract: The reduction process of NOx species stored over Pt-Ba/Al2O3 Lean NOx Trap systems is analysed in this paper when H2 is used as a reductant. The effect of different experimental conditions (temperature, reductant concentration, adsorption lengths, etc.) is addressed and discussed in relation to the selectivity and the efficiency of the reduction process.

Identification of the reaction networks of the NOx storage/reduction in lean NOx trap systems

Abstract: The reaction network of the NO x storage and reduction over Pt−Ba/Al 2 0 3 ‘lean NO x trap’ catalysts is presented in this paper. The NO x storage was investigated at first. The collected results showed that a dual pathway is operating when starting from NO/O 2 mixtures: the first route implies the well-known oxidation of NO to NO 2 , and its subsequent adsorption via disproportionation to form nitrates (nitrate route), whereas the second novel route consists of a stepwise oxidation of NO in the presence of oxygen to form nitrite ad-species, which are progressively oxidized to nitrates (nitrite route). Then the reduction of stored NO x with hydrogen is addressed. The bulk of data points out that the reduction of stored nitrates occurs under near isothermal conditions through a Pt-catalysed surface reaction that does not involve the thermal desorption of the stored nitrates as a preliminary step. A specific role of a Pt−Ba interaction was suggested, which plays a role in the NO x storage phase as well. The effect of the operating conditions (temperature, presence of CO 2 and water) on both adsorption-reduction phases has been also analysed.

The NOx Reduction Mechanism by H2 under near Isothermal Conditions over Pt–K/Al2O3 Lean NOx Trap Systems

Abstract: The reduction of NO x stored over a Pt–K/Al2O3 Lean NO x Trap is analyzed when H2 is used as reductant. An in series 2-steps process is herein proposed, involving at first the formation of NH3 upon reaction of nitrates with H2 (step 1), followed by the reaction of NH3 with residual nitrates to give N2 (step 2).

High-efficiency catalytic system

Abstract: A catalytic system for treating exhaust gases of lean burn engines comprising two catalyst beds connected in parallel, each of which includes a catalyst comprising one or more noble metals and one or more oxides of alkaline or alkaline -earth metal, wherein said catalytic beds alternatively and cyclically operate under conditions of adsorption of the nitrogen oxides released from the exhaust gases of an engine, and under conditions of reduction of said adsorbed nitrogen oxides to give nitrogen using a reducing agent, characterized in that said reducing agent is supplied to the catalyst bed, operating under reducing conditions, in controlled amounts, such as to minimize the production of by-products of said reduction reaction and extend the catalyst life.