III International Conference

PP-II-138EFFECT OF Zr ON THE OXIDATION STATE OF Pd AND CATALYTIC ACTIVITYOF THE SOL-GEL PREPARED Pd/Al 2 O 3 -ZrO 2 CATALYSTSTiznado H. 1, 2 , Simakov A. 1 , Zaera F. 2 , Fuentes S. 11 Centro de Ciencias de la Materia Condensada-UNAM, Ensenada, Mexico2 University of California Riverside, Riverside, USAE-mail: hugot@ucr.eduThe catalytic properties of Pd-only catalysts supported in Al 2 O 3 -ZrO 2 have a dependenceon the concentration of ZrO 2 . It is shown that by controlling the support characteristics it canbe improved the catalytic activity for the CO oxidation. CO adsorption shows a clearinfluence of the ZrO 2 concentration over the oxidation state of palladium and the physicalproperties of the supports.IntroductionThe palladium-only three-way catalyst has been developed by the catalytic industry toachieve better elimination of the cars exhaust gases, especially during the cold-start [1]. Thistype of catalysts has substituted advantageously the Pt-Rh or Pd-Rh catalysts in the catalyticconverters, since it has been found that under close-loop operation conditions palladium canmeet the properties of the bi or three-metallic catalysts. Some challenges remain in theoptimization of these catalysts, as, diminishing the concentration of palladium, improving thethermo-stability, reducing NOx in presence of oxygen excess, improving the selectivity tonitrogen, etc. With the aim of design improved palladium-only catalysts, we started a study ofpreparation of mixed oxides of Al 2 O 3 with additives of La 2 O 3 [2], ZrO 2 [3] and CeO 2 [4]using the sol-gel technique. In this work the effect of zirconia over the properties of thecatalysts of Pd supported in Al 2 O 3 will be addressed.Results and DiscussionMixed Al 2 O 3 -ZrO 2 supports were prepared with different ZrO 2 concentrations (1.6, 4.7,8.0, 12.2, 20.8 and 44 wt %), using the sol-gel method. The solids were calcined at 650 o C,and then impregnated with a palladium chloride solution to give a concentration of 0.3 wt% ofpalladium. The surface areas were determined by N 2 adsorption, finding a maximum area forthe catalyst containing 4.7 wt% of ZrO 2 . CO adsorption monitored by infrared spectroscopywas one of the techniques used to characterize the properties of the Pd surface. It wasobserved that different species of CO adsorbed are formed both on the support and on thepalladium, depending on the ZrO 2 concentration and the pretreatment conditions. CO species415