Applied Catalysis B: Environmental 22 (1999) 123–133 Extraordinarily effective promotion by sodium in emission control catalysis: NO reduction by propene over Na-promoted Pt/-Al 2 O 3 I.V. Yentekakis a,∗ , M. Konsolakis a , R.M. Lambert b , N. Macleod b , L. Nalbantian c a Department of Chemical Engineering, University of Patras and ICE/HT-FORTH, Patras, GR-26500, Greece b Departmentt of Chemistry, University of Cambridge, Lensfield Road, CB2 1EW, Cambridge, UK c CPERI-FORTH, P.O. Box 361, Thermi, 57001 Thessaloniki, Greece Received 1 February 1999; received in revised form 9 April 1999; accepted 10 April 1999 Abstract The catalytic activity and selectivity of Pt dispersed on -Al 2 O 3 , for the reduction of NO by propene is promoted extremely strongly by sodium in the temperature range 470–770 K. Remarkable and unprecedented effects on both activity and selectivity are found. Rate increases by two orders of magnitude are achievable, while the selectivity towards to N 2 is improved from ∼20% over the Na-free unpromoted Pt catalyst, to >95% over the optimally Na-promoted catalyst. The Na-free Pt is almost ineffective for the NO + C 3 H 6 reaction over the gas composition and temperature range of this investigation. The promoting effect is due to a sodium-induced increase in the strength of Pt–NO chemisorption relative to propene on a catalyst surface predominantly covered by propene and its fragments. This is accompanied by weakening of the N–O bond, thus facilitating NO dissociation, which process is proposed as the critical reaction initiating step. ©1999 Elsevier Science B.V. All rights reserved. Keywords: NO reduction; Propene; Platinum; Sodium; Alkali; Promotion; XRD; HREM 1. Introduction Heterogeneous catalysis has and will continue to play a major role in pollution control. It provides best solution for reduction of NO x and oxidation of VOCs produced by mobile and stationary combustion pro- cesses [1–17]. Recent reviews of the field reveal the importance of the subject and the urgency with which advances are sought [1–5]. Currently, ‘three-way’ catalytic converters (TWCs) are used for the simultaneous removal of all three main pollutants (NO x , CO and hydrocarbons) from auto- ∗ Corresponding author. Fax: +30-61-993255; e-mail: yyentek@iceht.forth.gr motive emissions [2,3]. These use formulations based variously on Pt, Pd and Rh. Although TWCs are very effective in oxidising CO and hydrocarbons they are substantially less effective in reducing the NO x emis- sions, especially under lean-burn conditions. With re- gard to NO x reduction, note that Pt is relatively inef- fective for the dissociative chemisorption of NO [9], whereas Palladium exhibits strong structure sensitiv- ity for this process, which is favoured by step sites and elevated temperatures [10,11]. On the other hand Rh is highly effective for NO dissociative chemisorp- tion and is therefore, the key component responsible for NO x reduction in TWCs. Considerable effort has recently been expended on enhancing the catalytic properties of Pt-group metals 0926-3373/99/$ – see front matter ©1999 Elsevier Science B.V. All rights reserved. PII:S0926-3373(99)00042-9 Δημοσίευση Α6