Maria Auxiliadora Scaramelo Baldanza

The nature of metal oxide on adsorptive and catalytic properties of Pd/MeOx/Al2O3 catalysts

Abstract The role of ceria, niobium and molybdenum oxides on the promotion of the NO reduction by CO was studied. A bifunctional mechanism was discussed as a function of both the nature of interaction between metal oxide and palladium and the redox properties of each metal oxide. The NO dissociation was better on the Pd/MoO 3 /Al 2 O 3 catalyst than on the Pd/CeO 2 /Al 2 O 3 and Pd/Nb 2 O 5 /Al 2 O 3 catalysts. The explanation for the very high N 2 production on Pd–Mo catalyst during the TPD analysis may be attributed to the NO+Me δ + stoichiometric reaction. The promoting effect of a reducible oxide for the NO+CO reaction at low temperature can be ascribed mainly to its easiness for a redox interchange and its interaction with the noble metal particles. This would increase the surface redox ability and favor the dynamic equilibrium needed for high N 2 selectivity.

NO reduction with ethanol on MoO3/Al2O3 and CeO2-ZrO2-supported Pd catalysts

Abstract The reduction of NO with ethanol on MoO 3 /Al 2 O 3 and CeO 2 -ZrO 2 -supported Pd catalysts was studied. The Pd/CeO 2 -ZrO 2 sample showed higher activity for the conversion of NO and higher selectivity for N 2 formation when compared to the Pd-MoO 3 /Al 2 O 3 sample. The CO chemisorption results showed that the CeZr mixed oxide chemisorbed a higher amount of CO, and this is related to a higher reducibility capacity of this compound when compared to MoO 3 . Furthermore, TPD analysis of adsorbed NO and ethanol showed that the Pd/CeO 2 -ZrO 2 catalyst has a higher ability of dissociating NO to N 2 and of decomposition of ethanol with the formation of CO 2 . Also, TPSR experiments showed that on Pd-8Mo/Al 2 O 3 , ethanol competes with NO for adsorption sites on partially reduced molybdenum oxide. This was not the case for the Pd/Ce 0.75 Zr 0.25 O 2 catalyst, where both NO and ethanol adsorb and decompose on the partially reduced mixed oxide surface. These facts are probably related to the better performance of this catalyst in relation to the Pd-MoO 3 /Al 2 O 3 catalyst for the NO + ethanol reaction.

Methane activation on alumina supported platinum, palladium, ruthenium and rhodium catalysts

Abstract Methane activation was conducted on Pt, Pd, Ru and Rh alumina supported catalysts. Simultaneously with the gas chemisorption, H 2 , CO 2 and CO were evolved from all the catalyst surfaces. The H2 evolution resulted from the association of hydrogen atoms provided from dissociative chemisorption of methane. CO and CO 2 evolution was explained by the partial migration of carbon adspecies, from metal surface to the metal-support interface, followed by their interaction with the alumina O 2− ions.

NO reduction in presence of methane and ethanol on Pd-Mo/Al2O3 catalysts

The reduction of nitric oxide by methane and ethanol on Pd/Al 2 O 3 and Pd-8%Mo/Al 2 O 3 was studied. TPSR analyses of NO+CH 4 revealed that above 560 K methane reacted with NO on palladium sites. On Pd-8Mo/alumina, NO decomposition was also observed. The NO+CH4 reaction, at 723 K on both catalysts showed high NO conversion and selectivity for N 2 . The presence of water did not affect the NO conversion, however, selectivity towards N 2 was lower on the Pd-8Mo/alumina catalyst. The NO+ethanol results suggested that ethanol and NO competed for the same active sites. However, the presence of MoO 3 improved the selectivity for N 2 formation during reaction at 593 K.