Preparation of Carbon Nanofiber-Supported Platinum and Ruthenium Catalysts Comparison of Ion Exchange and Homogeneous Deposition Precipitation
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چکیده
Carbon nanofiber (CNF)-supported platinum catalysts have been prepared using Pt(NH3)4(NO3)2 as precursor by two different ion exchange techniques, one at a constant pH and one in which the pH is gradually and homogeneously increased from 3 to 6 by hydrolysis of urea. The latter method resembles the procedure of homogeneous deposition precipitation (HDP). Characterization of the CNF support was performed by acid-base titration, TGA-MS and XPS and for the various platinum catalysts TEM, H2-chemisorption and XRF/ICP-AES were utilized. With both synthesis techniques, from diluted precursor solutions, homogeneously distributed, highly dispersed and thermally stable metal particles were obtained with an average particle size of 1-2 nm. With the HDP method for the Pt/CNF catalysts a linear relationship between the number of acidic oxygen-containing groups on the surface of activated CNF and the metal loading has been found. For the highest loaded catalyst a platinum/adsorption site ratio of 0.5 was established, corresponding to about 0.7 Pt(NH3)4 2+ molecules/nm 2 . Furthermore it has been established that with this procedure higher platinum loadings (~4 wt%) can be achieved that with the ion exchange procedure (<2 wt%). The HDP method using RuNO(NO3)3(H2O)2 also turned out to be suitable for the preparation of small (1-2 nm) uniform ruthenium particles on CNF with a high thermostability.
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