Pt-s up ported Nanocrystalline Ceria-Zirconia Doped with La, Pr or Gd: Factors Controlling Syngas Generation in Partial Oxidation/autothermal Reforming of Methane or Oxygenates

摘要

Nanocrystalline CeO_2-ZrO_2 (Ce:Zr 1:1) samples doped with La, Pr or Gd cations (containing up to 30 at.%) were prepared via the Pechini route. Pt (1.4 wt.%) was supported via impregnation with H_2PtCl_6 solution followed by drying and calcination. The samples' surface features were studied by SIMS and FTIRS of adsorbed CO. The oxygen mobility was characterized by the dynamic oxygen isotope exchange and H_2 TPR. Catalytic activity was studied in the flow installation using diluted feeds (0.7% CH_4 +0.5% O_2 or 1% C_3H_6O + 0.5% O_2 +0.5% H_2O in He). In the selective oxidation of methane (POM), the catalytic activity correlates with Pt dispersion controlled by the oxidized sample's ability to stabilize Pt~(2+) cations as precursors of small reactive Pt clusters formed under reaction conditions. This is favoured by a larger doping cation (La) and a developed network of nanodomain boundaries. At comparable Pt dispersion, the highest performance was demonstrated by a La-doped system, which correlates with the highest surface/near-surface oxygen mobility controlled by the strength of Ce-O bonds in the surface layer. In the autothermal reforming of acetone, the activity trends differ from those in POM because of the more prominent role of the oxygen mobility required to prevent surface coking.