Noble metal nanoparticles supported onto semiconducting oxides as catalysts for reduction reactions

• Ano de defesa: 2019
• Autor(a) principal: Barbosa, Eduardo César Melo
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: Catálise; Catalysis; Eletrocatálise; Eletrocatalysis; Fotocatálise; Nanoparticles; Nanopartículas; Photocatalysis; Plasmônica; Plasmonics; Semiconductors; Semicondutores
• Link de acesso: http://www.teses.usp.br/teses/disponiveis/46/46136/tde-24102019-114537/

This thesis has as main objective to contribute to the field of catalysis employing nanomaterials composed of TiO2, Au/TiO2, SiO2, Au/SiO2, Pt/TiO2, Fe2O3, and Pd/Fe2O3 towards reduction reactions. Firstly, Au/TiO2 and Au/SiO2 were explored as catalysts for the hydrogenation of 4-nitrophenol under plasmonic excitation, while the hydrogen source was varied between H2(g) and BH4-(aq). These changes led to different reaction pathways, and we found that the plasmonic excitation of Au can lead to negative effects over the activities under some conditions. The underlying physical reason was explored using density functional theory calculations. We observed that positive versus negative effects on the plasmonic catalytic activity is reaction-pathway dependent. These results shed important insights on our current understanding of plasmonic catalysis, demonstrating reaction pathways must be taken into account for the design of plasmonic nanocatalysts. The TiO2 samples were then employed as templates for the deposition of Pt nanoparticles with different loadings. Subsequently, these materials were supported onto carbon for the electrocatalytic reduction of oxygen. By optimizing the loading of Pt at the TiO2 surface, the electrocatalytic activity towards the activity of them could be improved compared to the commercial Pt/C material, even at lower Pt loadings. The enhancement in activities could be assigned to the balance between Pt loading and generation of reactive surface sites, such as adsorbed oxygenated species. Moreover, the utilization of TiO2 as support enabled improved stabilities relative to commercial Pt/C. These results may inspire the development of electrocatalysts for the oxygen reduction reaction with improved activities and stabilities. Lastly, nanomaterials composed of Pd nanoparticles supported onto iron oxide were employed as catalysts on the reduction of styrene oxide. We investigated the effects of a capping agent onto the activity and selectivity of the catalyst. It was observed that the removal of the polymeric stabilizer enabled us to achieve an inverted selectivity and a higher activity of the material. This gives us a different view of the role of a stabilizer in nanocatalysis and opens up the possibility of tailoring the selectivity. We believe that the results presented herein shed important insights into our understanding of nanocatalysis by controlled metal nanoparticles.