Estudos da oxidação eletroquímica de etanol em catalisadores multifuncionais
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Data
2021-10-27
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Universidade Estadual Paulista (Unesp)
Resumo
O estudo da oxidação eletroquímica de etanol foi realizado em catalisadores baseados em nanopartículas de Pt e Pd suportadas em misturas de carbono e óxidos metálicos (MOx = Co3O4, Fe3O4, Sb2O3, In2O3 e Bi2O3). As nanopartículas de Pt e Pd foram sintetizadas pelo método de poliol modificado e de transferência de fases, respectivamente. Os materiais foram caracterizados por difração de raios X (DRX), microscopia eletrônica de transmissão (TEM), espectroscopia de absorção de raios X (XAS), e técnicas eletroquímicas (voltamentria cíclica, cronoamperometria). Os resultados da caracterização revelaram que o parâmetro de rede e a distância Pt-Pt nos catalisadores Pt/C-MOx são semelhantes aos de Pt/C, e que as nanopartículas de Pt tem tamanho médio de 2,8 nm e estão bem distribuídas nos suportes. As propriedades eletrônicas estudadas por XAS em meio ácido e alcalino revelaram que os suportes e a presença de etanol na solução modificam os estados eletrônicos da banda 5d da Pt. O desempenho eletrocatalítico para a reação de oxidação de etanol avaliado em solução ácida e alcalina mostrou que os catalisadores Pt/C-M3O4 (M=Co, Fe) apresentaram maior atividade em ambos os meios e o catalisador Pt/C-In2O3 somente em meio ácido, em relação ao catalisador Pt/C. Os resultados obtidos para os catalisadores Pd/C-MOx e Pd/C indicam que os materiais não apresentaram variação no parâmetro de rede do Pd, que as partículas de Pd tem tamanho médio de 2,6 nm, com distribuição homogênea no suporte. Os suportes híbridos afetam os estados eletrônicos da banda 4d do Pd. A atividade catalítica para oxidar etanol foi menor que a atividade do Pd/C. Embora tenham sido observadas variações de atividade catalítica para a oxidação de etanol e mudanças nas propriedades eletrônicas que dependem do óxido incorporado no suporte, não se encontrou uma correlação entre a atividade e os estados eletrônicos da banda d do metal catalisador. Pode se afirmar com base nos resultados que os diferentes suportes afetam a atividade catalítica da Pt e do Pd para oxidar etanol, envolvendo provavelmente efeitos eletrônicos e geométricos e a capacidade do óxido de fornecer espécies oxigenadas procedentes de hidroxilas adsorvidas na sua superfície.
The study of the electrochemical oxidation of ethanol was carried out on catalysts containing Pt and Pd nanoparticles supported on mixtures of carbon and metal oxides (MOx = Co3O4, Fe3O4, Sb2O3, In2O3 and Bi2O3). Pt and Pd nanoparticles were synthesized by a modified polyol and by a phase-transfer method, respectively. The materials were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray absorption spectroscopy (XAS) and by electrochemical techniques (cyclic voltammetry, chronoamperometry). The characterization results revealed that the lattice parameter and the Pt-Pt distance in Pt/C-MOx catalysts are similar to those of Pt/C, and that Pt nanoparticles have average size of 2.8 nm and are well distributed on the supports. The electronic properties studied by XAS in acid and alkaline media revealed that the supports and the presence of ethanol in the solution modify the electronic states of the Pt 5d band. The electrocatalytic performance towards ethanol oxidation evaluated in acid and alkaline solution showed that Pt/C-M3O4 (M=Co, Fe) catalysts exhibited higher activities in both media and the Pt/C-In2O3 only in acid, as compared to the Pt/C catalyst. The results obtained for Pd/C-MOx and Pd/C catalysts indicate that these materials do not show variations in the Pd lattice parameter and that Pd particles have mean size of 2.6 nm and are homogeneously distributed on the supports. The hybrid supports affect the electronic states of the Pd 4d band. The catalytic activity for ethanol oxidation was lower than the activity of Pd/C. Even though variations in catalytic activity for ethanol oxidation and changes in the electronic properties, which depend on the oxide incorporated to the support, were observed, a correlation between activity and the electronic states of the d band of the catalytic metal was not found. It is possible to say, based on the results, that the different supports affect the catalytic activity of Pt and Pd for the oxidation of ethanol, probably involving electronic and geometric effects and the capacity of the oxide to provide oxygenated species from hydroxyls adsorbed on their surface.
The study of the electrochemical oxidation of ethanol was carried out on catalysts containing Pt and Pd nanoparticles supported on mixtures of carbon and metal oxides (MOx = Co3O4, Fe3O4, Sb2O3, In2O3 and Bi2O3). Pt and Pd nanoparticles were synthesized by a modified polyol and by a phase-transfer method, respectively. The materials were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray absorption spectroscopy (XAS) and by electrochemical techniques (cyclic voltammetry, chronoamperometry). The characterization results revealed that the lattice parameter and the Pt-Pt distance in Pt/C-MOx catalysts are similar to those of Pt/C, and that Pt nanoparticles have average size of 2.8 nm and are well distributed on the supports. The electronic properties studied by XAS in acid and alkaline media revealed that the supports and the presence of ethanol in the solution modify the electronic states of the Pt 5d band. The electrocatalytic performance towards ethanol oxidation evaluated in acid and alkaline solution showed that Pt/C-M3O4 (M=Co, Fe) catalysts exhibited higher activities in both media and the Pt/C-In2O3 only in acid, as compared to the Pt/C catalyst. The results obtained for Pd/C-MOx and Pd/C catalysts indicate that these materials do not show variations in the Pd lattice parameter and that Pd particles have mean size of 2.6 nm and are homogeneously distributed on the supports. The hybrid supports affect the electronic states of the Pd 4d band. The catalytic activity for ethanol oxidation was lower than the activity of Pd/C. Even though variations in catalytic activity for ethanol oxidation and changes in the electronic properties, which depend on the oxide incorporated to the support, were observed, a correlation between activity and the electronic states of the d band of the catalytic metal was not found. It is possible to say, based on the results, that the different supports affect the catalytic activity of Pt and Pd for the oxidation of ethanol, probably involving electronic and geometric effects and the capacity of the oxide to provide oxygenated species from hydroxyls adsorbed on their surface.
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Nanopartículas, Platina, Paládio, Óxidos metálicos, Etanol