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Shape Changes of Pt Nanoparticles Induced by Deposition on Mesoporous Silica

GIOVANETTI, LISANDRO J.; RAMALLO-LOPEZ, JOSE M.; FOXE, MICHAEL; JONES, LOUIS C.; KOEBEL, MATTHIAS M.; SOMORJAI, GABOR A.; Craievich, Aldo Felix; SALMERON, MIQUEL B.; REQUEJO, FELIX G.
Fonte: WILEY-BLACKWELL; MALDEN Publicador: WILEY-BLACKWELL; MALDEN
Tipo: Artigo de Revista Científica
ENG
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Polyvinylpyrollidone (PVP)-capped platinum nanoparticles (NPs) are found to change shape from spherical to flat when deposited on mesoporous silica substrates (SBA-15). Transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), and extended X-ray absorption fine structure (EXAFS) analyses are used in these studies. The SAXS results indicate that, after deposition, the 2 nm NPs have an average gyration radius 22% larger than in solution, while the EXAFS measurements indicate a decrease in first neighbor co-ordination number from 9.3 to 7.4. The deformation of these small capped NPs is attributed to interactions with the surface of the SBA-15 support, as evidenced by X-ray absorption near-edge structure (XANES).; LNLS [D04B-XAFS1-7683]; LNLS; PIP (CONICET, Argentina); PIP (CONICET, Argentina) [112-200801-03079]; ANPCYT [PICT-2008-00038]; ANPCyT; CNPq [PICT-2008-00038]; CNPq; Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division, under the Department of Energy [DE-AC02-05CH11231]; Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division, under the Department of Energy

High Pressure and Low Temperature Study of Ammonia Borane and Lithium Amidoborane

Najiba, Shah
Fonte: FIU Digital Commons Publicador: FIU Digital Commons
Tipo: Artigo de Revista Científica Formato: application/pdf
Relevância na Pesquisa
26.28%
Hydrogen has been considered as a potentially efficient and environmentally friendly alternative energy solution. However, one of the most important scientific and technical challenges that the “hydrogen economy” faces is the development of safe and economically viable on-board hydrogen storage for fuel cell applications, especially to the transportation sector. Ammonia borane (BH3NH3), a solid state hydrogen storage material, possesses exceptionally high hydrogen content (19.6 wt%).However, a fairly high temperature is required to release all the hydrogen atoms, along with the emission of toxic borazine. Recently research interests are focusing on the improvement of H2 discharge from ammonia borane (AB) including lowering the dehydrogenation temperature and enhancing hydrogen release rate using different techniques. Till now the detailed information about the bonding characteristics of AB is not sufficient to understand details about its phases and structures. Elemental substitution of ammonia borane produces metal amidoboranes. Introduction of metal atoms to the ammonia borane structure may alter the bonding characteristics. Lithium amidoborane is synthesized by ball milling of ammonia borane and lithium hydride. High pressure study of molecular crystal provides unique insight into the intermolecular bonding forces and phase stability. During this dissertation...

High pressure and low temperature study of ammonia borane and lithium amidoborane

Najiba, Shah
Fonte: FIU Digital Commons Publicador: FIU Digital Commons
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
26.28%
Hydrogen has been considered as a potentially efficient and environmentally friendly alternative energy solution. However, one of the most important scientific and technical challenges that the "hydrogen economy" faces is the development of safe and economically viable on-board hydrogen storage for fuel cell applications, especially to the transportation sector. Ammonia borane (BH3NH 3), a solid state hydrogen storage material, possesses exceptionally high hydrogen content (19.6 wt%).However, a fairly high temperature is required to release all the hydrogen atoms, along with the emission of toxic borazine. Recently research interests are focusing on the improvement of H2 discharge from ammonia borane (AB) including lowering the dehydrogenation temperature and enhancing hydrogen release rate using different techniques. Till now the detailed information about the bonding characteristics of AB is not sufficient to understand details about its phases and structures. ^ Elemental substitution of ammonia borane produces metal amidoboranes. Introduction of metal atoms to the ammonia borane structure may alter the bonding characteristics. Lithium amidoborane is synthesized by ball milling of ammonia borane and lithium hydride. High pressure study of molecular crystal provides unique insight into the intermolecular bonding forces and phase stability. During this dissertation...

Films delgados mesoporosos de óxidos metálicos, mixtos e híbridos. Hacia un diseño racional de nanomateriales funcionales; Mesoporus metallic, mixed and hybrid oxide thin films. Towards a rational design of functional nanomaterials

Angelomé, Paula C.
Fonte: Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires Publicador: Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires
Tipo: info:eu-repo/semantics/doctoralThesis; tesis doctoral; info:eu-repo/semantics/publishedVersion Formato: application/pdf
Publicado em //2008 SPA
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36.52%
Los óxidos mesoporosos son materiales que presentan poros monodispersos (de tamaños de entre 2 y 50 nm) altamente ordenados, de elevada área específica (100 - 1000 m2/g). Se sintetizan mediante la combinación de dos procesos: reacciones sol gel, que dan lugar al material inorgánico o híbrido, y autoensamblado de moléculas anfifílicas, que actúan como molde de los poros. Entre las aplicaciones de estos materiales se encuentran: (foto)catálisis, sorción, sensores y otros dispositivos, etc. En este trabajo se realizó un estudio de la síntesis de films delgados mesoporosos de óxidos metálicos, mixtos e híbridos orgánico-inorgánicos. Estos films delgados se obtuvieron mediante dip coating a través del proceso conocido como Autoensamblado Inducido por Evaporación, y fueron caracterizados mediante una gran variedad de técnicas de microscopía, espectroscopia y difracción, de manera de conocer cabalmente la estructura a nivel micro, meso y macroscópico. En una primera parte, se presenta la síntesis de films delgados mesoporosos de TiO2, ZrO2 y óxidos mixtos Ti-Si, Zr-Si. En todos los casos, se estudió la relación existente entre la estructura del material obtenido y las condiciones de síntesis (composición del sol...

Síntese de aluminossilicatos mesoporosos a partir de sementes de zeólitas Y e ZSM-5; Synthesis of aluminosilicate mesoporous from ZSM-5 and Y zeolite seeds

Guimarães, Carlos Eduardo Pontes
Fonte: Universidade Federal de Alagoas; Brasil; Programa de Pós-Graduação em Engenharia Química; UFAL Publicador: Universidade Federal de Alagoas; Brasil; Programa de Pós-Graduação em Engenharia Química; UFAL
Tipo: Dissertação
POR
Relevância na Pesquisa
36.52%
Currently there is a clear trend of increased production of heavier oils, as oil reserves with better quality are being depleted. This implies the development of new refining technologies for the processing of these oils in order to maximize the acquisition of liquid fuels that are the main demand of the markets. The main process of refining is the fluidized catalytic cracking (FCC process) that requires an acid catalyst able to crack the hydrocarbon molecules present in the feed. The problem is that the current catalysts, formulated with Y zeolite, which has small pores, do not allow access of large molecules. This project will be studied the synthesis of mesostructure materials from a gel formed by seeds of Y and ZSM-5 zeolites. Therefore, in this project, we studied the synthesis of materials mesoestruturados from a gel formed by seeds of zeolite Y and ZSM-5 which has been submitted or not to adjust the pH to the range of 8-10 by addition of acid. From the physico-chemical characterizations was observed that all samples formed a phase mesoporous MCM-41 type. It was found that the materials synthesized from seeds of zeolite ZSM-5 had evidence of the presence of seeds of the solid mesoporous zeolites, regardless of whether or not samples subjected to pH adjustment. While the materials synthesized from seeds of zeolite Y with only those adjust the gel pH to the range 8 to 10 before the hydrothermal crystallization seeds showed evidence of the X-ray diffractograms and infrared spectra...