Chemical Engineering Science 59 (2004) 4313 – 4323 www.elsevier.com/locate/ces Effect of periodic operation on the low-temperature activity for propane oxidation over Pt /Al 2 O 3 catalysts Per-Anders Carlsson a, b, c , ∗ , Stephanie Mollner a, e , 1 , Karl Arnby a, d , Magnus Skoglundh a, d a Competence Centre for Catalysis, Chalmers University of Technology, SE-412 96 Göteborg, Sweden b Department of Chemical Engineering and Environmental Sciences, Chalmers University of Technology, SE-412 96 Göteborg, Sweden c Department of Applied Physics, Chalmers University of Technology, SE-412 96 Göteborg, Sweden d Department of Materials and Surface Chemistry, Chalmers University of Technology, SE-412 96 Göteborg, Sweden e Institut für Chemische Verfahrenstechnik, Universität Karlsruhe, D-76128 Karlsruhe, Germany Received 6 April 2004; received in revised form 28 May 2004; accepted 15 June 2004 Abstract We report experimental results for the oxidation of propane over alumina supported platinum catalysts with varying Pt dispersions. Flow- reactor experiments introducing 0.15 vol% C 3 H 8 while changing the oxygen concentration step-wise (step-response experiments) from rich to lean composition or periodically (pulse-response experiments) switching between rich and lean O 2 concentrations, at a constant inlet gas temperature of 250 ◦ C have been performed. Complementary in situ FTIR spectroscopy experiments for surface analysis have also been carried out. The results reveal a strong correlation between the reactant composition and the catalytic activity, showing an optimum reaction rate for compositions close to the stoichiometric value for complete oxidation of propane. For lean gas compositions the activity is low probably due to a high O-coverage (O self-poisoning) which in turn is likely to also cause platinum oxide formation. However, by periodically introducing rich periods (periodic operation) the activity can temporarily be restored and the surface composition can be kept close to the optimum, leading to an overall improvement of the oxidation rate. Generally, the introduction of short rich periods to a slightly lean mixture (lean–rich cycling) seems to be more efficient than the corresponding rich–lean cycling since the latter suffers from oxygen deficiency limiting the reaction during the long periods.  2004 Elsevier Ltd. All rights reserved. Keywords: Catalytic oxidation; O self-poisoning; Platinum oxide; C 3 H 8 ; Transient experiments; DRIFT 1. Introduction The heterogeneous catalytic oxidation of hydrocarbons (HC) is essential in pollution control for both stationary and mobile applications (Heck and Farrauto, 2001). For the latter, the introduction of the three-way catalyst (TWC) in 1979 has meant a remarkable success, by now decreasing ∗ Corresponding author. Department of Chemical Engineering and En- vironmental Sciences, Competence Centre for Catalysts, Chalmers Uni- versity of Technology, Göteborg 41296, Sweden. Tel.: +46-31-772-3025; fax: +46-31-772-3035. E-mail address: perc@chemeng.chalmers.se (P.-A. Carlsson). 1 Present address: BASF AG, Carl-Bosch-Str. 38 67056 Ludwigshafen, Germany. 0009-2509/$ - see front matter  2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.ces.2004.06.024 the emission levels of HC, as well as CO and NO x , by more than 90% (Calvert et al., 1993). Despite this encouraging development of catalytic concepts, there are still some key questions that need to be solved. One is related to the gen- erally low catalytic activity at low temperatures. For a TWC to convert hydrocarbons sufficiently, a minimum operation temperature of 250–300 ◦ C is required (Heck and Farrauto, 2001; Bosteels and Heck, 2002). This is the reason for the “cold-start emissions” (Samenfink et al., 2002), which ac- counts for 50–90% of the total HC emissions from automo- tives (Heck and Farrauto, 2001; Gandhi et al., 2003). It is therefore important to find routes to improve the catalytic low-temperature activity for an appreciable conversion of exhausts immediately after a start of a cold engine.