Preparation of palladium loaded carbon nanotubes and activated carbons for hydrogen sorption

Single wall carbon nanotubes (SWNTs) and MAXSORB activated carbon have been used as the support of palladium nanoparticles. The preparation of the palladium loaded carbon materials has been done by direct reaction between the support and a Pd (0) compound, either Pd-2(dba)(3).CHCl3 or Pd(PPh3)(4). The efficiency of the loading reaction has been much better when Pd-2(dba)(3).CHCl3 has been chosen as the Pd source, reaching high palladium loadings (up to ca. 45 wt.%) with relatively small particle size (5-10 nm for SWNTs and 30-40 nm for MAXSORB). The hydrogen isotherms of the palladium loaded materials present a steep increase at very low pressures. The H/Pd atomic ratio of the samples has been found to be dependent on the Pd precursor, being higher in the case of Pd2 (dba)3 -CHCl3. Several samples have achieved H/Pd ratios higher than the value for bulk Pd (H/Pd approximate to 0.6-0.7). Maximum hydrogen sorption at room temperature in the palladium loaded samples has been found to be of 0.5 wt.% at atmospheric pressure. Oxidative treatments on the substrate before the palladium loading have diminished the efficiency of the loading reaction, the hydrogen adsorption, and the H/Pd atomic ratio. (C) 2006 Elsevier B.V. All rights reserved.