Süperkritik depozisyon tekniği ile tekli Ni ve çift-metalli Pt-Ni nanokatalizör sentezi

Monometallic nickel and bimetallic platinum-nickel nanoparticles were deposited on ?-Al2O3, Vulcan XC72R and carbon aerogel (CA) supports by supercritical carbon dioxide (scCO2) deposition (SCD). Characterization of the samples was carried out by BET, TPD, XRD, TEM, and EDXS. Nickel acetylacetonate (Ni(acac)2) was adsorbed on the supports from scCO2 solutions. The adsorbed Ni precursor was reduced to nickel nanoparticles by heat treatment under hydrogen. The resulting nanoparticles had an average size of 6 nm. Bimetallic Pt-Ni nanoparticles were synthesized by a two-step procedure termed sequential deposition. First, Pt nanoparticles were deposited on the supports by adsorption of platinum cyclooctadiene dimethyl Pt(cod)(me)2 from scCO2 solution followed by reduction of the adsorbed precursor to Pt by heat treatment at 200 oC under flowing nitrogen. Subsequently, Ni(acac)2 was adsorbed on Pt/support from scCO2. The adsorbed Ni precursor was then reduced to Ni by heat treatment under hydrogen. Spherical nanoalloys of Pt-Ni nanoparticles with uniform sizes of ~3nm were obtained over Vulcan XC 72R, and Pt-Ni nanoparticles with uniform sizes of ~1nm were successfully synthesized over carbon aerogel. As for the alumina support, supported Pt-Ni nanoparticles of ~3 nm in size were obtained. The small composition variations in EDXS measurements indicated a uniform distribution of the bimetallic nanoparticles. The effect of the order of sequential deposition of Pt and Ni on both morphology and activity of the synthesized materials were also investigated. It was found that the formation of Ni nanoparticles occurs on the previously deposited Pt islands resulting in bimetallic spherical nanoparticles having homogeneous chemical compositions with no phase separation when Pt deposition is carried out first and this is followed by Ni deposition. Interestingly, the size of the bimetallic nanoparticles was found to be smaller than the size of the monometallic Ni. However, pure Ni agglomerates were observed on TEM images when Ni deposition is achieved first and this was followed by Pt addition. Cyclic voltammograms of the carbon supported catalysts were also determined. Bimetallic nanocatalysts showed a higher activity than the monometallic nanocatalysts. Among the bimetallic nanocatalysts, higher activity was obtained when Pt deposition was carried out first.