abstracts - Институт катализа им. Г.К. Борескова

PL-2INVESTIGATION OF REDOX REACTIONS MECHANISM: POTENTIAL IMPACTON CATALYST DESIGN. CASE STUDY OF HYDROGEN PRODUCTION ANDPURIFICATION ON CERIA-BASED MATERIALSMirodatos C., Sadykov V.A. 1Institut de Recherches sur la Catalyse, CNRS, 2 avenue Albert Einstein, F-69626,Villeurbanne Cedex, France1 Boreskov Institute of Catalysis SB RAS, Novosibirsk, RussiaE-mail: Claude.Mirodatos@catalyse.cnrs.frIn general, the key information for understanding a complex heterogeneous (gas/solid)catalytic process is to have access to the effective role of the surface by identifying andquantifying surface active sites and active adspecies coverage under steady-state operatingconditions. Among the most efficient techniques for accessing these data, in operandospectroscopies like DRIFT allow direct visualisation of surface occupancy, but often only themost abundant and stable, therefore the less active adspecies or even simple reactionspectators are detected [1, 2]. Another powerful technique is transient kinetics analysis that iscarried out by allowing the reaction to reach steady-state, i.e., under adsorption-desorptionreactionequilibrium, and then applying a stepwise change of feed gas concentration or evenbetter isotopic gas composition. The latter is known as steady-state isotopic transient analysis(SSITKA) [3]. The analysis of the transient responses enables a quantitative determination ofthe concentrations of adsorbed active intermediates species, as well as their rates of formationand consumption, revealing the main elementary steps on the catalyst surface. Finally, theconventional kinetic analysis under steady-state conditions where kinetic data are acquired byvarying P, T and W/F conditions and then modelled according different sets of rate equationsalso permits to determine surface concentrations. This approach consists of constructing ascheme of the reaction mechanism based on plausible elementary steps among which one (orsometimes several) is designated to be the rate-determining step. All other steps are assumedto be in quasi-equilibrium. The sorption of reactants and products is assumed to take placeaccording to a model of adsorption such as the Langmuir isotherm. Once the parameters ofthe rate equation have been estimated through regression analysis of the experimental data,the use of the sorption model and a site balance allows calculating the surface coverage of theintermediate species. However, often the drawback of challenging discrimination betweenseveral close models or coupled variables may lead to major uncertainties in operating surfacedescription.9