Kinetic study of SO2 oxidation over Pd-Pt bimetallic catalysts

Marina  Cortes-Reyes, University of Virginia

Diesel Oxidation Catalysts composed of a Pd and Pt metal combination show high activity and sintering resistance for their use as after-treatment systems. Nevertheless, they are still sensitive to sulfur and the oxidation of SO₂ to SO₃ that can occur has only been briefly studied [1-5]. Pt:Pd ratio and particle size are both know to influence intermediate sulfur surface species stabilities and likely oxidation also. A series of Pd-Pt/γ-Al₂O₃ catalysts were prepared using incipient wetness impregnation with different metal ratios, keeping the molar concentration of total metal equivalent to 1wt% of Pd for all the samples. The materials were calcined at different temperatures between 550 and 700C in order to modify the particle size. CO chemisorption was carried out in a Micromeritics ASAP 2020 Chemisorption system and was used to obtain the metal dispersion, the metallic surface area and the particle size. Steady-state oxidation studies were performed over catalysts with different precious metal composition and similar particles sizes or same metal ratio but different sizes. Different concentrations of SO₂, O₂ and SO₃ were used to obtain oxidation kinetics. Global reaction orders with respect to SO₂, O₂ and SO₃ were estimated. Kinetic parameters were obtained working without mass transfer limitations and far from the equilibrium.

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