Estudo dos efeitos de suportes híbridos carbono-óxido na oxidação de metanol sobre nanopartículas de Pd
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Data
2022-02-08
Autores
Araújo, Thayná Pereira de
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Universidade Estadual Paulista (Unesp)
Resumo
Neste trabalho foi realizado o estudo da influência de óxidos MO2 (CeO2, SnO2) e M3O4 (Co3O4, Fe3O4) no suporte de nanopartículas Pd para a reação de oxidação do metanol. As nanopartículas metálicas foram sintetizadas em estado coloidal utilizando um método de transferência de fases, sendo posteriormente utilizadas frações idênticas da suspensão coloidal para preparar os catalisados contendo nanopartículas de Pd suportadas em misturas carbono-óxido. A caracterização física dos materiais foi feita por difratometria de raios X (DRX) e microscopia eletrônica de transmissão em modo varredura (STEM). A caracterização eletroquímica foi realizada por voltametria cíclica em meio ácido e meio alcalino. A avaliação da atividade catalítica dos materiais para a reação de oxidação do metanol foi realizada por medidas cronoamperométricas em solução alcalina contendo metanol. As imagens de microscopia eletrônica de transmissão em modo varredura evidenciaram que, como esperado, a síntese pelo método de transferência de fases permitiu produzir catalisadores que apresentaram nanopartículas de Pd com uma estreita faixa de tamanho, além de mostrar partículas metálicas distribuídas homogeneamente sobre os diferentes suportes. A área eletroquimicamente ativa do Pd foi calculada a partir da carga de redução de uma monocamada de PdO e também pela carga de oxidação de uma monocamada de CO, obtidas por voltametria cíclica e experimentos de oxidação de CO adsorvido em meio ácido, respectivamente. Além de todos os materiais apresentaram áreas semelhantes, os resultados calculados pelos dois métodos mostraram boa concordância. Os estudos de oxidação de metanol mostraram diferenças significativas na atividade catalítica do Pd nos diferentes suportes. Como todos os materiais contêm nanopartículas de Pd idênticas, é possível atribuir as diferenças observadas na atividade catalítica aos efeitos dos diferentes óxidos presentes nos suportes híbridos. Os resultados obtidos mostram que, com exceção do SnO2, os óxidos incorporados ao suporte neste trabalho melhoram a atividade catalítica do Pd para a reação de oxidação do metanol.
In this work, the study of the influence of oxides MO2 (CeO2, SnO2) and M3O4 (Co3O4, Fe3O4) in the support of Pd nanoparticles for the methanol oxidation reaction was performed. The Pd nanoparticles in colloidal state were synthesized using a phase transfer method, and then identical fractions of the colloidal suspension were used to prepare catalysts containing Pd nanoparticles supported in carbon-oxide mixtures. The physical characterization of the materials was executed by X-ray diffraction (XRD) and scanning mode transmission electron microscopy (STEM). The electrochemical characterization was performed by cyclic voltammetry in acid and alkaline medium. The evaluation of the catalytic activity of the materials for the methanol oxidation reaction was done by chronoamperometric measurements in alkaline solution containing methanol. Transmission electron microscopy images in scanning mode evidence that, as expected, the synthesis by allowed producing catalysts having Pd nanoparticles within a narrow size range and homogeneously distributed on the different supports. The electrochemically active area of Pd was calculated from the reduction charge of a PdO monolayer and also from the charge of oxidation of a CO monolayer, obtained by cyclic voltammetry and CO stripping measurements in acidic medium, respectively. In addition to all materials having similar areas, the results calculated by the two procedures show very good agreement. The studies of methanol oxidation showed significant diferences in the catalytic activity of Pd on the different supports. Because the Pd nanoparticles were identical for all materials, it is possible to attribute the differences in catalytic activity observed to the effects of the different oxides in the hybrid supports. The results obtained in this work show that, with exception of SnO2, the oxides incorporated to the supports improve the catalytic activity of Pd for the methanol oxidation reaction.
In this work, the study of the influence of oxides MO2 (CeO2, SnO2) and M3O4 (Co3O4, Fe3O4) in the support of Pd nanoparticles for the methanol oxidation reaction was performed. The Pd nanoparticles in colloidal state were synthesized using a phase transfer method, and then identical fractions of the colloidal suspension were used to prepare catalysts containing Pd nanoparticles supported in carbon-oxide mixtures. The physical characterization of the materials was executed by X-ray diffraction (XRD) and scanning mode transmission electron microscopy (STEM). The electrochemical characterization was performed by cyclic voltammetry in acid and alkaline medium. The evaluation of the catalytic activity of the materials for the methanol oxidation reaction was done by chronoamperometric measurements in alkaline solution containing methanol. Transmission electron microscopy images in scanning mode evidence that, as expected, the synthesis by allowed producing catalysts having Pd nanoparticles within a narrow size range and homogeneously distributed on the different supports. The electrochemically active area of Pd was calculated from the reduction charge of a PdO monolayer and also from the charge of oxidation of a CO monolayer, obtained by cyclic voltammetry and CO stripping measurements in acidic medium, respectively. In addition to all materials having similar areas, the results calculated by the two procedures show very good agreement. The studies of methanol oxidation showed significant diferences in the catalytic activity of Pd on the different supports. Because the Pd nanoparticles were identical for all materials, it is possible to attribute the differences in catalytic activity observed to the effects of the different oxides in the hybrid supports. The results obtained in this work show that, with exception of SnO2, the oxides incorporated to the supports improve the catalytic activity of Pd for the methanol oxidation reaction.
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Catalisadores, Nanopartículas, Óxidos metálicos, Eletroquímica, Células a combustível