ORIGINAL PAPER Insight into the Role of Electropositive Promoters in Emission Control Catalysis: An In Situ DRIFTS Study of NO Reduction by C 3 H 6 Over Na-Promoted Pt/Al 2 O 3 Catalysts M. Konsolakis • I. V. Yentekakis Ó Springer Science+Business Media New York 2013 Abstract The nature and the relative population of adsorbed species formed on the surface of unpromoted and Na-promoted Pt/c-Al 2 O 3 catalysts, during the NO reduc- tion by propene, was investigated by means of in situ dif- fuse reflectance infrared Fourier transform spectroscopy, in an effort to elucidate the pronounced effect of electropos- itive promoters in emission control catalysis. It was found that under steady-state reaction conditions the surface of the unpromoted catalyst is mainly covered by carbon containing species, such as hydrocarbon fragments, car- boxylates and cyanides. On the opposite, the surface of Na-promoted catalysts is predominantly covered by NOx ad-species, carbonyls and isocyanates, implying the sig- nificant effect of Na promoter on surface species formation. To further gain insight into the effect of Na-promoter on the nature and the reactivity of ad-species, the transient respond of IR spectra under the cycle: NO ? He ? C 3 H 6 ? NO, is also investigated. The results imply that over Na-free catalysts the interaction of propene with NOx pre-adsorbed species (mainly nitrates) leads to the formation of strongly bonded carboxylates and cyanides, which are inactive towards NO. In contrast, NO interaction with the surface of Na-promoted catalysts results in the formation of nitro/nitrite species as well as to nitrosyls, which are highly active towards propene, leading to active intermediates such as isocyanates (NCO). The present results demonstrate that the excellent catalytic performance of Na-promoted cata- lysts can be well interpreted on the basis of these significant modifications induced by electropositive promoters on cat- alysts surface chemistry. Keywords Sodium promotion Á Pt/Al 2 O 3 Á NO Á C 3 H 6 Á DRIFTS Á Isocyanates 1 Introduction Nowadays, the abatement of NOx, CO and HCs automotive emissions constitute a subject of major environmental importance, because of the major contribution of the above pollutants to serious environmental problems, such as photochemical smog, acid rain and greenhouse effect [1]. In this context, three-way catalytic converters (TWCs) have been employed, for more than 30 years, to success- fully control automotive exhaust emissions. Although, TWCs represent a well established technology, several problems related to TWCs operation, cost and efficiency, are still exist and should be overcomed. Among them, the most important include the use of scarce and expensive Rh, the emission of N 2 O byproduct, the reconciliation of TWCs with the upcoming legislations as well as the noble metals recycling due to the coexistence of Pt (and/or Pd) with Rh [1]. Motivated by the above aspects, our research efforts have been lately focused on the development of low cost, Rh-free, TWCs with enhanced catalytic performance and thermal durability. In this perspective, it has been found that the activity and selectivity of Pt or Pd metals can be notably enhanced by structural and surface promoters M. Konsolakis (&) Á I. V. Yentekakis Laboratory of Physical Chemistry and Chemical Processes (PCCP), Department of Sciences, Technical University of Crete, 73100 Chania, Crete, Greece e-mail: mkonsol@science.tuc.gr 123 Top Catal DOI 10.1007/s11244-013-9947-y