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Publisher Summary This chapter presents the effect of the reductant nature on the catalytic removal of nitrous oxide (N2O) on an iron (Fe)-zeolite-beta catalyst. A Fe(97)-BEA catalyst, prepared by conventional ion-exchange procedure and calcined at 773 K, almost contains iron-binuclear-oxo-species in charge compensation of the BEA structure. The re-oxidation of iron (II) species by N2O leads to new oxo-species reducible at lower temperature than the dimer species. Among hydrogen (H2), carbon monoxide (CO), propene, and ammonia (NH3) in the reduction of N2O, CO, propene, and NH3 are selective reductants. For these three reductants, a similar light-off temperature of ca 638 K is obtained in the selective catalytic reduction of N2O. CO is efficient from 473 K, but its activity is limited by the reoxidation of Fe II to Fe III species by N2O.

The selective catalytic reduction (SCR) by NH3 is the most important technology to control the emissions of NOx from stationary sources. A new mechanism is proposed for the SCR of NO on Cu-exchanged FAU catalysts which markedly differs from that occurring on the V2O5-TiO2 catalysts; NO takes part in the reoxidation of Cu+ to Cu2+, but not of V4+ to V5+. This conclusion was achieved by decomposing the catalytic cycle into the oxidation and reduction steps of Cu species by reactant mixtures composed of NO, O2, and NH3 and the comparison with the global SCR reaction. A quantum chemical (QM) modeling of the catalytic site has been untertaken, leading to a better knowledge of the Cu electronic structure.

A Fe-exchanged zeolite beta is shown to be very active in the reduction of N20 to N2 by NH3 in presence of O2. The temperature of 50% N20 conversion is lower by ca 80 K than that of its catalytic decomposition in absence of NH3. Kinetics with 14N20 and 15NH3 has shown that N20 is converted at ca 86% through N-0 splitting and 14% N-N splitting. The former reaction involves the redox cycle Fe3+ ↔ Fe2+ where the active species are likely binuclear Fe oxocations. This conclusion was reached from TPR, TPO and TPD experiments. The intimate mechanism and the sites responsible for N-N splitting were not yet identified.

Activity in n-butane isomerization reaction of various alkaline salts of H 3 PW 12 O 40 and H 4 SiW 12 O 40 was shown to be strongly dependent on the strength and number of accessible protons whereas the stability with time on stream was correlated to the presence of mesoporosity. For the liquid iC 4 /C 4 =continuous alkylation reaction, the strength and the number of acid sites appeared less important than the existence of mesoporosity indicating that the diffusion of the reactants and of the products plays an important role in this reaction.