Formation and Growth of Pd Nanoparticles Inside a Highly Cross-Linked Polystyrene Support: Role of the Reducing Agent

Simultaneous time-resolved SAXS and XANES techniques were employed to follow in situ the formation of Pd nanoparticles in a porous polystyrene support, using palladium acetate as a precursor and gaseous H-2 or CO as reducing agents. These results, in conjunction with data obtained by diffuse reflectance UV-vis and DRIFT spectroscopy and TEM measurements, allowed unraveling of the different roles played by gaseous H-2 and CO in the formation of the Pd nanoparticles. In particular, it was found that the reducing agent affects (i) the reduction rate (which is faster in the presence of CO) and (ii) the properties of the hosted nanoparticles, in terms of size (bigger with CO), morphology (spherical with H-2, triangular-like with CO), and surface properties (unclean with CO). The importance of a multitechnique approach in following the whole process of metal nanoparticles formation clearly emerges.