from first principles PP-I-1

OP-III-3Sulphur Ageing Mechanisms on Pd/BaCeO 3·2ZrO 2 Catalyst for MethaneCombustionFinocchio E. 1 , Specchia S. 21 Università di Genova, Department of Chemical and Process Engineering, Genova, Italy2 Politecnico di Torino, Department of Applied Science and Technology, Torino, Italystefania.specchia@polito.itThe ageing effect induced by S-compounds (added as odorants in the natural gas network forsafety purposes) over 2% Pd/BaCeO 3·2ZrO 2 catalysts for CH 4 combustion was studied. Thecatalysts were prepared by solution combustion synthesis [1], starting from metalnitrates/glycine mixtures. Basic characterization (XRD, BET, FESEM, TPD/R/O analysis),FT-IR studies and catalytic activity tests were performed in fresh status and after acceleratedageing carried out up to 500 h (hydro-thermal treatment at 800 °C under a flow of 9% CO 2 ,18% H 2 O, 2% O 2 in N 2 , including 200 ppmv of SO 2 to emphasize any poisoning effect).With ageing, TPO analysis demonstrated that the catalyst was heavily poisoned after 170 h(T 50 from 512 to 628 °C); then it recovered the catalytic activity after 340 h, with a resultingperformance better than in the fresh status (T 50 equal 443 °C). Finally, after 500 h the catalystresulted poisoned again, by reaching a T 50 of 595 °C. Skeletal spectra of the fresh and 170 haged catalysts showed carbonate species on the perovskite structure. With prolonged ageing,bulk sulphate species appeared, affecting mostly the support, namely the ceriate structure,forming Ba sulphate, due to diffusion mechanisms in the catalyst structure [2]. Pd depositionincreased bulk sulphate formation during ageing with respect to the support. Prolonged ageingalso leaded to the disappearance of the perovskite structure. Low temperature CO adsorptionexperiments allowed the characterization of Pd state. The main bands of the fresh samplespectra were assigned to CO coordinated over Pd ions highly dispersed and stronglyinteracting with the support and Pd metal particles [3]. Following prolonged ageing, thebehavior of the catalysts significantly differed: all IR bands were strongly reduced inintensity, with a main peak likely due to CO coordinated over Pd ions [4]. Prevailing ageingmechanisms resulted in the oxidation of the surface Pd metal particles and surface-bulksulfates formation, the latter destroying the starting crystallographic structure.References:[1] S. Specchia, C. Galletti, V. Specchia, Stud. Surf. Sci. Catal. 175 (2010) 59.[2] P. Bazin, O. Saur, J.C. Lavalley, G. Blanchard, et al., Appl. Catal. B: Environ. 13 (1997) 265.[3] T. Schalow, B. Brandt, M. Laurin, S. Schauermann, et al., J. Catal. 242 (2006) 58.[4] S. Specchia, E. Finocchio, G. Busca, P. Palmisano, V. Specchia, J. Catal. 263 (2009) 134.46