abstracts - Институт катализа им. Г.К. Борескова

PL-2This presentation will focus on the way to access to a qualitative/quantitative activesurface description obtained from the above mentioned methodologies in order to convergetowards more advanced and consolidated mechanisms.The chosen application domain is the production and purification of hydrogen on ceriabasedmaterials for which both laboratories have carried out a large range of physicochemical,kinetic and mechanistic investigations.Ceria-based mixed oxides (Ce x M 1–x O y ) are versatile solid oxygen exchangers. At hightemperatures (400–800ºC) the redox cycle Ce 3+ ⇔ Ce 4+ + e – facilitates oxygen storage andrelease from the bulk fluorite lattice. When combined with noble or non noble metal particles,this makes them ideal candidates for catalytic and/or electrocatalytic oxidation applicationssuch as natural gas partial oxidation into syngas (POX) for feeding solid-oxide fuel cells.However, the surface redox chemistry of ceria is sensitive even at low temperatures to crystalstructure defects, which can be tuned by substituting some of the Ce cations with ions ofdifferent size and/or charge [4, 5]. In that low T domain, other reactions related to fuel celltechnology (especially proton-exchange membrane –PEM- cells) are particularly attractive forsmall-scale domestic and automotive applications. As such, hydrogen enrichment andpurification by water gas shift (WGS) and CO preferential oxidation (PrOx) aim at decreasingthe CO concentration in hydrogen below 10 ppm, as required for steady-state operation ofPEM FC.In the case of platinum catalysts supported on mixed oxides the rate of oxygen supplyfrom the support may determine the rate of methane oxidation and especially the selectivitytowards syngas. In addition, it is known that among the various supports able to provideactive oxygen species, CeO 2 based solid solutions are capable themselves to oxidize both CH 4and CO even in the absence of gas phase oxygen, at least for a transient period [6, 7]. Theexact and respective role of the metal and of the support (as oxygen generator either fromgaseous oxygen or water) as a function of the applied operating conditions has to be clearlyidentified in order to design improved materials able to be both highly active and selectiveover a wide range of operating conditions, as required for any commercial application.In this presentation, the effects of doping ceria supports of platinum catalysts for the threereactions: CH 4 POX, CO PrOx in the presence of H 2 , WGS/RWGS are investigated bytransient kinetics and in operando DRIFT analysis. On the basis of the observed transientresponses, different reaction schemes are proposed. Modelling of the experimental responsesaccording to these schemes is used to validate or reject the respective models, depending onthe fitness between calculated and experimental transient curves.10