Influência de óxidos de metais de transição na eletrocatálise da reação de redução do oxigênio em nanopartículas de Pt e de Pd
Carregando...
Data
2019-01-15
Autores
Ometto, Felipe Berto [UNESP]
Título da Revista
ISSN da Revista
Título de Volume
Editor
Universidade Estadual Paulista (Unesp)
Resumo
Nesse trabalho foram estudados os efeitos na eletrocatálise da reação de redução de oxigênio da incorporação de óxidos (CeO2, SnO2, TiO2, ZrO2 e WO3) nos suportes de nanopartículas de Pt e de Pd. Os catalisadores foram preparados pelo método do poliol modificado visando controlar parâmetros como tamanho e forma das partículas metálicas, que poderiam influenciar a atividade catalítica. Através de experimentos de absorção de raios X in situ foi possível constatar que a interação entre as partículas metálicas e o suporte altera a densidade eletrônica tanto na banda 5d da Pt quanto na banda 4d do Pd. Os dados de espectroscopia de fotoelétrons excitados por raios X, no entanto, mostraram que essa interação não foi suficiente para alterar a energia de ligação dos orbitais 4f da Pt e 3d do Pd. Para os catalisadores contendo nanopartículas de Pt, (Pt/CeO2/C, Pt/SnO2/C, Pt/TiO2/C, Pt/ZrO2/C e Pt/WO3/C) os resultados de experimentos de difração de raios X indicaram que os parâmetros de rede e distância entre átomos de Pt são similares. Imagens de microscopia eletrônica de transmissão de alta resolução mostraram que o tamanho e forma das partículas de Pt são similares. Assim, as modificações na atividade catalítica para a reação de redução do oxigênio observadas podem ser atribuídas exclusivamente à variação das propriedades eletrônicas provocada pela interação metal-suporte. Comparando-se os dados de absorção de raios X com os obtidos nos estudos eletroquímicos foi observado que em meio ácido a atividade catalítica aumenta conforme a banda 5d da Pt é preenchida. Em meio alcalino, observou-se que quanto mais vazia a banda 5d da Pt maior a atividade catalítica para a redução de oxigênio sendo todos os materiais com óxido mais ativos que Pt/C. Os catalisadores de Pd (Pd/CeO2/C, Pd/SnO2/C, Pd/TiO2/C, Pd/ZrO2/C e Pd/WO3/C) mostraram uma correlação entre atividade catalítica para a redução de oxigênio em meio ácido e a diminuição da vacância eletrônica da banda 4d do Pd que foi avaliado da análise dos espectros de absorção de raios X obtidos em vácuo. De modo geral, a reação de redução de oxigênio ocorre principalmente por um mecanismo de 4 elétrons em todos os materiais de Pt e de Pd estudados, tanto em meio ácido quanto em meio alcalino.
In this work, the effects on the electrocatalysis of the oxygen reduction reaction of the incorporation of oxides (CeO2, SnO2, TiO2, ZrO2 e WO3) into the supports of Pt and Pd nanoparticles were studied. The catalysts were prepared by a modified polyol method aiming to control parameters such as size and shape of the metal nanoparticles, which could influence the catalytic activity. Through in situ X-ray absorption experiments, it was possible to verify that the interaction between the metal particles and the support alters the electronic density of the Pt 5d band as well as of the Pd 4d band. Data of X-ray photoelectron spectroscopy, however, showed that this interaction was not sufficient to alter the Pt 4f and Pd 3d binding energies. For the catalysts having Pt nanoparticles (Pt/CeO2/C, Pt/SnO2/C, Pt/TiO2/C, Pt/ZrO2/C e Pt/WO3/C), the results of experiments of X-ray diffraction indicated that lattice parameters and distance between Pt atoms were alike. High-resolution transmission electron microscopy showed Pt particles had similar sizes and shapes. Thus, the changes in catalytic activity for oxygen reduction could be attributed solely to the variation of electronic properties promoted by metal-support interactions. Comparison of the X-ray absorption data with those obtained in the electrochemical studies showed that in acid medium the catalytic activity increases as the Pt 5d band is more filled. In alkaline medium, it was observed that as the Pt 5d band became emptier, the catalytic activity increased, being higher than on Pt/C for all the materials containing oxide. Pd catalysts (Pd/CeO2/C, Pd/SnO2/C, Pd/TiO2/C, Pd/ZrO2/C e Pd/WO3/C) showed a correlation between the catalytic activity for oxygen reduction in acid medium and the electronic occupation of the Pd 4d band that evaluated from X-ray absorption experiments done in vacuum. In general, the oxygen reduction reaction occurs mainly through a 4-electron mechanism on all Pt and Pd catalysts studied, in acid as well as in alkaline medium.
In this work, the effects on the electrocatalysis of the oxygen reduction reaction of the incorporation of oxides (CeO2, SnO2, TiO2, ZrO2 e WO3) into the supports of Pt and Pd nanoparticles were studied. The catalysts were prepared by a modified polyol method aiming to control parameters such as size and shape of the metal nanoparticles, which could influence the catalytic activity. Through in situ X-ray absorption experiments, it was possible to verify that the interaction between the metal particles and the support alters the electronic density of the Pt 5d band as well as of the Pd 4d band. Data of X-ray photoelectron spectroscopy, however, showed that this interaction was not sufficient to alter the Pt 4f and Pd 3d binding energies. For the catalysts having Pt nanoparticles (Pt/CeO2/C, Pt/SnO2/C, Pt/TiO2/C, Pt/ZrO2/C e Pt/WO3/C), the results of experiments of X-ray diffraction indicated that lattice parameters and distance between Pt atoms were alike. High-resolution transmission electron microscopy showed Pt particles had similar sizes and shapes. Thus, the changes in catalytic activity for oxygen reduction could be attributed solely to the variation of electronic properties promoted by metal-support interactions. Comparison of the X-ray absorption data with those obtained in the electrochemical studies showed that in acid medium the catalytic activity increases as the Pt 5d band is more filled. In alkaline medium, it was observed that as the Pt 5d band became emptier, the catalytic activity increased, being higher than on Pt/C for all the materials containing oxide. Pd catalysts (Pd/CeO2/C, Pd/SnO2/C, Pd/TiO2/C, Pd/ZrO2/C e Pd/WO3/C) showed a correlation between the catalytic activity for oxygen reduction in acid medium and the electronic occupation of the Pd 4d band that evaluated from X-ray absorption experiments done in vacuum. In general, the oxygen reduction reaction occurs mainly through a 4-electron mechanism on all Pt and Pd catalysts studied, in acid as well as in alkaline medium.
Descrição
Palavras-chave
Eletrocatalisadores, Reação de redução do oxigênio, Nanopartículas, Platina, Paládio, Interações metal-suporte, Eletrocatalysts, Oxygen reduction reaction, Nanoparticles, Platinum, Palladium, Metal-support interactions