III International Conference

PP-I-42MECHANISM OF CATALYTIC CO OXIDATION ON Pd(110) : FROM LOW TOATMOSPHERIC REACTION PRESSURESalanov A.N., Titkov A.I., Suprun E.A., Slavinskaya E.M., Boronin A.I.Boreskov Institute of Catalysis SB RAS, Novosibirsk, Russia,E-mail: salanov@catalysis.nsk.suCO reaction with oxygen on Pd(110) has been studied by XPS, LEED and massspectrometryat reagent pressures varied from 10 -7 to 10 5 Pa. At “low” pressures(10 -7 – 10 Pa) the reaction takes place on reconstructed Pd(1x2) surface between O ads andCO ads . The hysteresis observed in the reaction rate dependence on temperature is due tostructural transformations of the surface under the action of adsorbates. At atmosphericreagent pressures CO oxidation reaction is accompanied by the formation of surface and bulkPdO. The hysteresis observed in the reaction rate dependence on temperature at atmosphericreagent pressures is caused by the formation and reduction of bulk PdO particles.Pt, Pd and Rh metals are widely used as active components in catalysts for automobileexhaust neutralizers and in a number of important industrial processes, such as ammoniaoxidation, methane compbustion, etc. [1]. Pd is used in these catalysts due to its high activityin oxidation of hydrocarbons, CO and H 2 , as well as NO reduction. To understand themechanisms of catalytic reactions, it is necessary to study these reactions over metalmonocrystals in a wide reagent pressure range from very low (≤10 -6 torr) to atmospheric(~760 torr). The goal of this study was to investigate the mechanism of CO oxidation on Pd atreagent pressures varied from 10 -7 to 10 5 Pa. The investigation of this reaction over Pd(110) at“low” (10 -7 – 10 Pa) and atmospheric pressures at 350-700 K using mass-spectrometry, XPS,LEED, mathematical simulation showed that the mechanism of CO oxidation by oxygenchanges due to surface reconstruction, oxygen penetration into subsurface metal layers andformation of surface and bulk palladium oxides when the pressure increases from “low” toatmospheric .Both for “low” and atmospheric pressures the dependence of the reaction rate observedwhen the sample was heated in the flow of CO and O 2 (heating cycle) were substantiallydifferent from those observed during cooling (cooling cycle), resulting in a hysteresis. At“low” pressures and low temperatures ≤350-450 K the heating cycle reaction rates weresignificantly lower than those of the cooling one. It was found that such dependence of thereaction rate on temperature is due to the reconstruction of Pd(110) surface caused byadsorption and desorption of O 2 and CO, and reaction CO ads + O ads [2]. Thus, the reactionacceleration during heating is accompanied by the surface reconstruction Pd(1x2)-p(4x2)-CO83