Tailoring and stabilization of ultrafine rhodium nanoparticles on gamma-Al2O3 by troctylamine: Dependence of the surface properties on the preparation route

Rhodium nanoparticles supported on gamma-Al2O3 have been prepared by Metal Vapour Synthesis (MVS), using mesitylene solvated Rh atoms as starting material and working in the absence and in the presence of trioctylamine (TOA), as stabilizer. The size and surface features of the metal particles have been studied by Transmission Electron Microscopy (TEM) and by FT-IR spectroscopy of adsorbed carbon monoxide, and they have been compared with those of a commercial Rh/gamma-Al2O3 sample. The results indicated that by MVS technique nanoparticles significantly smaller in size and with a narrower size distribution than those present on the commercial sample were produced. The addition of TOA during the MVS process resulted in a further decrease in the metal particle size. IR spectra of adsorbed CO indicated that metal particles produced via MVS expose at their surface a larger fraction of Rh atoms in low coordination. They can be extracted by CO, forming volatile Rh carbonyls which migrate onto the support, where the metal atoms are oxidised to Rh(l). For Rh particles produced via MVS in the presence of TOA, such low coordinated sites appeared stabilised by adsorbed amine molecules.