The reduction of NO by propene over Ba-promoted Pt/γ-Al2O3 catalysts

The performance of Ba-promoted Pt/gamma -Al2O3 catalysts in the reduction of NO by propene has been investigated in a wide range of temperatures (ca. 200-500 degreesC), reactant partial pressures, and promoter loading. The reaction follows Langmuir-Hinshelwood-type kinetics, reflecting weaker adsorption of NO on the metal surface relative to C3H6 Both catalytic activity and selectivity are strongly promoted by Ba, which does not however induce a change in the reaction mechanism. Rate increases by 2 orders of magnitude are achievable for N-2 and CO2 production, while the selectivity toward N2 is also significantly improved with a gain of about 50-60 percentage units exhibited by optimally Ba-promoted Pt. Barium also suppressed the formation of the undesirable by-product CO. These effects are understandable in terms of the influence of the Ba promoter on the relative adsorption strengths of reactant species. Ba promotes the adsorption (increasing coverage) of electronegative adsorbates (NO) relative to the adsorption of electropositive adsorbates (propene) on a catalyst surface predominately covered by the hydrocarbon. This is accompanied by weakening of the N-O bond, thus facilitating NO dissociation. These effects operate together to produce large increases in both activity and selectivity. (C) 2001 Academic Press.