Estudo computacional da adsorção da molécula do óxido nítrico em aglomerados de paládio suportados em um modelo de y-alumina

• Autor(a) principal: Prates, Letícia Maia
• Data de Publicação: 2017
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Biblioteca Digital de Teses e Dissertações da UERJ
• Texto Completo: http://www.bdtd.uerj.br/handle/1/15827
• topic: y-alumina; palladiumclusters; NO; DFT; NBO; y-alumina; aglomerados de paládio; NO; DFT; NBO; CNPQ::CIENCIAS EXATAS E DA TERRA::QUIMICA::QUIMICA INORGANICA

The fuel burning in vehicles is the one of the main sources of pollutant emission to the atmosphere,being responsible to poor air quality,which leads to severe environmental problems and respiratory diseases in human beings. The increasing development of automotive industry led to improvements in fuels composition and injection systems and production of lighter components. However, even if these changes have reduced the emission levels, there is a constant growth of fleet causing anunfavorable balance. Three-way catalysts are devices found in vehicles, capable to convert the toxic substances released by the engine, such as NOx, CO and unburned hydrocarbons, in milder compounds to the atmosphere. For the NO molecule, specifically, noble metal (palladium and platinum) based catalystssupported inγ-alumina has shown high efficiency. However, the role of support in the adsorption of the molecule of interest is still not well known. The use of theoretical methods allows the investigation, in molecular level, of the processes involved during the interaction between the catalyst and the adsorbate. In this work, quantum-mechanical calculations using the Density Functional Theory were performed in order to obtain geometric, electronic and energetic parameters involved in the NO molecule adsorption on isolated and supported in y-alumina model (Al14O24H6) Pd4 clusters.The Al14O24H6 support promotes a higher dispersion of the palladium atoms on its surface. The NO adsorption in supported model is stronger on palladium atoms anchored on oxygen anions (ontop mode), with energy of 25.4 kcal/mol (computed at B3LYP/LANL2DZ/6-311+G(d)), in good agreement with the experimental value of 27.2 kcal/mol. The presence of y-alumina reduces the NO adsorption energy, mainly in bridge mode, where 91% of this decrease is consequence of electronic effect provided by support. Natural Bond Orbital calculations show that the higher the number of palladium atoms coordinated to NO, the greater 4d→2π*back-donation electronic transfer. However, this y-alumina model prevents the hollow mode formation on adsorbed Pd4 agglomerate. Thus, only in bridge mode is verified an effective electron transfer from 4d palladium orbital to2π* orbital in the NO molecule on supported Pd4. Electron transfers among palladium atoms are also verified. When the Pd Pd interactions are vanished (Pd1/Al14O24H6), it is possible to observe that tetrahedral aluminum (Altc) presents a clear acid behavior, whereas octahedral aluminum (Aloc), a slightly basic one.