RÉSUMÉ
In situ X-ray absorption spectroscopy and mass spectrometry measurements were employed to simultaneously probe the atom specific short range order and reactivity of Pd and PtPd nanoparticles towards NO decomposition at 300 °C. The nanoparticles were synthesized by a well controlled, eco-friendly wet chemical reduction of metal salts and later supported on activated carbon. Particularly for the bimetallic PtPd samples, distinct atomic arrangements were achieved using a seeding growth method, which allowed producing a random nanoalloy, or nanoparticles with Pt- or Pd-rich core. X-ray photoelectron spectroscopy, transmission electron microscopy, and X-ray diffraction provided additional insights on their electronic, morphological and long range order structural properties. The results revealed that the higher the thermal induced atomic migration observed within the nanoparticles during thermal treatments, the least were their reactivity for NO abatement.
RÉSUMÉ
A thermostimulated sol-gel transition in a system prepared by mixing a ZrOCl(2) acidified solution to a hot H(2)SO(4) aqueous solution was studied by dynamic rheological measurements and quasi-elastic light scattering. The effect of temperature and of molar ratio R(S) = [Zr]/[SO(4)] on the gelation kinetics was analyzed using the mass fractal aggregate growth model. This study shows that the linear growth of aggregates occurs at the early period of transformation, while bidimensional growth occurs at the advanced stage. The bidimensional growth can be shifted toward monodimensional growth by decreasing the aggregation rate by controlling the temperature and/or molar ratio R(S). EXAFS and Raman results gave evidence that the linear chain growth is supported by covalent sulfate bonding between primary building blocks. At the advanced stage of aggregation, the assembly of linear chains through hydrogen bonding gave rise to the growth of bidimensional particles.