%0 Journal Article %J Advanced Materials %D 2003 %T Medium effect on the electron cooling dynamics in gold nanorods and truncated tetrahedra %A Link, Stephan %A Hathcock, D. J. %A Nikoobakht, Babak %A El-Sayed, Mostafa A %X A study on the electron relaxation dynamics and thermal cooling of colloidal gold nanoparticles (see Figure) in air and water finds that the local energy exchange with the surrounding medium occurs on the picosecond time scale, comparable with the electron-phonon relaxation, while a slow heat dissipation by water ensures that the particles remain heated for hundreds of picoseconds. %B Advanced Materials %V 15 %P 393-+ %8 Mar %@ 0935-9648 %G eng %M WOS:000181713900003 %R 10.1002/adma.200390088 %0 Journal Article %J Journal of Catalysis %D 2003 %T Propene hydrogenation over truncated octahedral Pt nanoparticles supported on alumina %A Yoo, J. W. %A Hathcock, D. J. %A El-Sayed, Mostafa A %X Colloidal Pt nanoparticles synthesized by a 1 : 5 concentration ratio of K2PtCl4 to polyacrylate were loaded on nanoporous alumina using the impregnation method at room temperature. The deposited Pt particles, present on the external surfaces of the support, were characterized by transmission electron microscopy, which indicated predominantly truncated octahedral (TO) shapes with a mean diameter of 10 nm. Their catalytic performance in the hydrogenation of propene at 30-80 degreesC was studied as a test reaction. The initial rate, reaction order, rate constant, activation energy, and turnover frequency were determined. The activation energy was found to be 8.4 +/- 0.2 kcal/mol, which is slightly lower than results reported for other platinum systems (10-14 kcal/mol). The TO platinum nanoparticles have atom-high surface steps, ledges, and kinks, and these atomic-scale fine structures are expected to decrease the activation energy. The reactivity of the surface atoms in this nanoparticle is so high that above 50 degreesC side reactions leading to complete surface poisoning take place within a few minutes. The effect of the polymer concentration of the polyacrylate-capped TO Pt/Al2O3 on the hydrogenation catalytic activity was also investigated. (C) 2003 Elsevier Science (USA). All rights reserved. %B Journal of Catalysis %V 214 %P 1-7 %8 Feb %@ 0021-9517 %G eng %M WOS:000182615700001 %R 10.1016/s0021-9517(02)00136-7 %0 Journal Article %J Journal of Physical Chemistry A %D 2002 %T Characterization of pt nanoparticles encapsulated in Al2O3 and their catalytic efficiency in propene hydrogenation %A Yoo, J. W. %A Hathcock, D. J. %A El-Sayed, Mostafa A %X Pt nanoparticles supported in nanoporous Al2O3 catalyst are prepared by reduction of K2PtCl4 solution using 112 in the presence of Al2O3 and poly(acrylic acid) as capping; material. After thorough washing with water to remove Pt nanoparticles located on the external surface of the Al2O3 and drying at 70 degreesC for 12 h, they were used in propene hydrogenation to evaluate catalytic activity as measured by the value of the activation energy in the temperature range between 30 and 90 degreesC. The Pt nanoparticles are characterized by using transmission electron microscopy (TEM). The particles in Pt/Al2O3 are found to be encapsulated and uniformly dispersed inside the Al2O3; however, the size and shapes are not clearly seen. After extraction of the Pt nanoparticles from the Al2O3 channels by using an ethanol-diluted HF solution, various shapes such as truncated octahedral, cubic, tetrahedral, and spherical with a size around 5 nm are observed. The encapsulated particles have various shapes but are smaller in size than those prepared in K2PtCl4 solution with polyacrylate in the absence of Al2O3. Using FT-IR studies, the capping material initially used in Pt/Al2O3 is not found in the Al2O3 channels. This might be due to the fact that the polymer (average MW 2100) is too large to be accommodated within the Al2O3 pores. The nanopores of Al2O3 have several roles in the synthesis of these nanoparticles. It allows for uniform dispersion and encapsulation of Pt nanoparticles. It controls the Pt sizes with narrow distribution that is determined by the pore dimension (5.8 nm). It protects against metal particle aggregation and produces various shapes even in the absence of the capping material. Using these Pt nanoparticles, the catalysis of hydrogenation of propene gas was studied. The initial rates, reaction order, rate constants, and activation energy for the hydrogenation are determined by use of mass spectrometric techniques. The activation energy is found to be 5.7 kcal/mol, which is about one-half that previously reported for catalysis by Pt metal deposited in SiO2 and TiO2 synthesized by using H2PtCl6 and Pt(allyl)(2) by impregnation method. %B Journal of Physical Chemistry A %V 106 %P 2049-2054 %8 Mar %@ 1089-5639 %G eng %M WOS:000174369800021 %R 10.1021/jp0121318