abstracts - Институт катализа им. Г.К. Борескова

OP-III-21THE MECHANISM OF AMMONIA OXIDATION ON SINGLE CRYSTALS OFPt-GROUP METALSMatveev A.V., Weststrate C.J. 1 , Carabineiro S.A.C. 1 , Bakker J.W. 1 , Baraldi A. 2 ,Gorodetskii V.V., Nieuwenhuys B.E. 1Boreskov Institute of Catalysis SB RAS, Novosibirsk, Russia1 Leiden Institute of Chemistry, Leiden, The Netherlands2 Universite degli studi di Trieste and Laboratorio TASC-INFM, Trieste, ItalyE-mail: matveev@catalysis.ruAmmonia is a harmful byproduct of a number of catalytic reactions. It is produced inautomotive catalytic converters, arising from the reduction of nitric oxide by hydrogen. It ispresent in tail gases of ammonia and nitric acid production plants, and of electricity plants,where NO x is reduced by ammonia. The important question is to understand how theselectivity depends on the nature and structure of the catalyst. Important questions are:(a) specific differences in behavior of different surfaces of different platinum group metals;(b) effect of oxygen on decomposition of ammonia;(c) effect of surface structure on decomposition and oxidation of ammonia;The purpose of the present work is to study the adsorption and dissociation of ammonia onPt(410), Pt(111), Rh(100) and Ru(0001) single crystal surfaces, and to examine the effect ofpreadsorbed oxygen (O ads ). The mechanism of ammonia decomposition and oxidation wasstudied with TDS, TPR, HREELS, and XPS both at ultrahigh vacuum and ~10 -7 mbar conditions.Pt(111). NH 3 adsorption on the clean Pt(111) surface at 300K-400K proceeds withoutdissociation. HREELS spectra show characteristic bands of molecular NH 3ads . As the NH 3pre-covered Pt(111) surface is exposed to 3 L O 2 , HNO ads species and atomic N ads are formed,which are important intermediate species for the low temperature oxidation of NH 3 on Ptsurfaces. It has been found that HNO ads is highly active and produces H 2 O and N ads , viareaction with H ads .Pt(410). NH 3 adsorption on the clean Pt(410) surface at 100 K proceeds without dissociation,like on Pt(111) and other Pt planes [1]. XPS experiments show NH3 ads dissociation when O adsis present on the surface. The NH 3ads oxydehydrogenation starts at 150 K. NO ads and NO (g)are also observed, but only during experiments in which an excess of O ads is available. NO adsdesorbs/decomposes between 400 K and 500 K. The ammonia oxidation reaction showsselectivity towards N 2 and H 2 O for low temperature, but the selectivity changes toward NOand H 2 O for higher temperatures. The exact temperature depends on the NH 3 :O 2 ratio. Wewere able to correlate surface coverage with the selectivity that is observed in the gas phase.Our results are compared to available literature data and to similar results that were obtainedfor Ir surfaces.Ru(0001). NH 3 decomposition and oxidation have been studied in the temperature rangebetween 150-1000 K. In contrast to Pt-surfaces, Ru(0001) is more efficient in decomposition361