Estudos da eletro-oxidação de etanol em nanocatalisadores de PdNi e PdCu
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Data
2017-03-07
Autores
Milian, Rosendo Parra [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
Esse trabalho consistiu em sintetizar, caracterizar e avaliar o desempenho catalítico para a oxidação de etanol de catalisadores contendo nanopartículas de PdCu e PdNi com diferente conteúdo do segundo metal (Cu e Ni em 10, 20, 30, 40 e 50%). A síntese foi realizada pelo método do poliol modificado e as nanopartículas foram suportadas em carbono de alta área superficial. Os catalisadores de PdCu e PdNi sintetizados foram caracterizados por difração de raios-X (DRX), microscopia eletrônica de transmissão em modo varredura (STEM), espectroscopia fotoeletrônica de raios-X (XPS) e espectroscopia de absorção de raios-X (XAS). A caracterização eletroquímica foi feita por voltametria cíclica em meio ácido e alcalino. A atividade catalítica foi avaliada por cronoamperometria em solução alcalina contendo etanol. De forma geral, os dados mostraram a incorporação do segundo metal (Cu e Ni) na estrutura cristalina do Pd que resulta na contração da rede cristalina, nanopartículas pequenas (menores que 5 nm) e presença de aglomerados. Tanto para PdCu quanto para PdNi, a formação de liga com o segundo metal produz um aumento da ocupação eletrônica da banda 4d do Pd. A presença de espécies oxidadas tem efeito oposto, ou seja, produz uma diminuição do preenchimento da banda. No caso de PdCu, os dados de XPS indicaram uma diminuição da quantidade de Pd metálico na superfície. O efeito contrário foi observado para PdNi. As atividades catalíticas para a oxidação de etanol foram menores que para Pd, diferentemente do que mostram a maioria dos dados da literatura. Resultados de espectroscopia de absorção-reflexão no infravermelho por transformada de Fourier (FTIRAS) mostraram que em todos os casos o principal produto da oxidação de etanol é acetato. PdCu/C (70:30) e PdNi/C (90:10) foram os catalisadores que apresentaram maior atividade catalítica para a oxidação de etanol em meio alcalino no seus respetivos conjuntos.
This work consisted in the synthesis, characterization and evaluation of the catalytic performance for the oxidation of ethanol of catalysts containing PdCu and PdNi nanoparticles with different contents of the second metal (Cu and Ni at 10, 20, 30, 40 and 50%). The synthesis was carried out by a modified polyol method and the nanoparticles were supported on high surface area carbon. Catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy scanning mode (STEM), X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The electrochemical characterization was done by cyclic voltammetry in acid and alkaline medium. The catalytic activity was evaluated by chronoamperometry in alkaline solution containing ethanol. In general, data showed incorporation of the second metal (Cu and Ni) into the crystal structure of Pd that results in the contraction of the Crystal lattice, small particles (smaller than 5 nm) and the presence of agglomerates. For PdCu as well as for PdNi, the formation of alloy with the second metal produces an increase in the electronic occupancy of the Pd 4d band. The presence of oxidized species has the opposite effect, i.e., produces a decrease in the band filling. For PdCu, XPS data indicated a decrease in the percentage of metallic Pd on the surface. The opposite was observed for PdNi. The catalytic activities for the oxidation of ethanol were lower than for Pd, differently from what most data in the literature show. Results of measurements by Fourier transformed absorption-reflection infrared spectroscopy showed that the main product of the oxidation of ethanol is, in all cases, acetate. The PdCu/C (70:30) and PdNi/C (90:10) exhibited the highest catalytic activity for ethanol oxidation in alkaline solution of the corresponding set of catalysts.
This work consisted in the synthesis, characterization and evaluation of the catalytic performance for the oxidation of ethanol of catalysts containing PdCu and PdNi nanoparticles with different contents of the second metal (Cu and Ni at 10, 20, 30, 40 and 50%). The synthesis was carried out by a modified polyol method and the nanoparticles were supported on high surface area carbon. Catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy scanning mode (STEM), X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The electrochemical characterization was done by cyclic voltammetry in acid and alkaline medium. The catalytic activity was evaluated by chronoamperometry in alkaline solution containing ethanol. In general, data showed incorporation of the second metal (Cu and Ni) into the crystal structure of Pd that results in the contraction of the Crystal lattice, small particles (smaller than 5 nm) and the presence of agglomerates. For PdCu as well as for PdNi, the formation of alloy with the second metal produces an increase in the electronic occupancy of the Pd 4d band. The presence of oxidized species has the opposite effect, i.e., produces a decrease in the band filling. For PdCu, XPS data indicated a decrease in the percentage of metallic Pd on the surface. The opposite was observed for PdNi. The catalytic activities for the oxidation of ethanol were lower than for Pd, differently from what most data in the literature show. Results of measurements by Fourier transformed absorption-reflection infrared spectroscopy showed that the main product of the oxidation of ethanol is, in all cases, acetate. The PdCu/C (70:30) and PdNi/C (90:10) exhibited the highest catalytic activity for ethanol oxidation in alkaline solution of the corresponding set of catalysts.
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Palavras-chave
Catalisadores à base de Pd, Oxidação de etanol, Eletrocatálise