Síntese e avaliação de catalisadores sol-gel destinados à reforma a vapor de metanol

• Autor(a) principal: Fornari, Arielle Cristina
• Data de Publicação: 2015
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Repositório Institucional da Universidade Estadual de Maringá (RI-UEM)
• Texto Completo: http://repositorio.uem.br:8080/jspui/handle/1/3829
• topic: Hidrogênio; Células a combustível; Metanol; Reforma a vapor; Catalisadores; Método sol-gel; Brasil.; Hydrogen; Fuel cells; Methanol steam reforming; CuO-ZnO-Al2O3 catalysts; Sol-gel method; Brazil.; Engenharias; Engenharia Química

This work aims to evaluate the activity and performance of catalysts CuO-ZnO-Al2O3 prepared by the sol-gel method applied in methanol steam reforming reaction for hydrogen production. To this end, five catalysts with different concentrations of Cu and Zn were synthesized, taking into account the composition of the commercial catalyst HiFUEL R120 supplied by Alfa Aesar®. They were denominated as follows: A1 (9% Cu), A2 (17% Cu), A3 (23% Cu), A4 (41% Cu) and A5 (48% Cu). The catalysts were previously characterized by Thermogravimetric Analysis (TG), specific surface area (BET) and total pore volume, X-ray Diffraction (XRD), Temperature Programmed Reduction (TPR), Temperature Programmed Desorption of Ammonia (TPD-NH3) and Scanning Electron Microscopy (SEM). The results of the characterizations (structural and textural) showed significant differences between the catalysts synthesized by the sol-gel method and the commercial. In addition, the properties of the sol-gel catalysts changed with the variation of their composition, especially with respect to the metal dispersion, which decreased with increasing the amount of Cu and Zn. With respect to the catalytic evaluation, all catalysts were tested for the methanol steam reforming reaction at 300 ºC. Under the experimental conditions used, there was no formation of CO, indicating that this reaction is interesting for the hydrogen production. In the catalytic tests, the HiFUEL R120 showed the highest conversion, followed by the catalyst A4 sol-gel. All catalysts showed deactivation during the reaction, due to sintering and coalescence of the Cu crystallites. The A2 and A3 catalysts presented the same catalytic behavior. Comparing the sol-gel catalysts, it was found that the catalytic activity increased with the active phase (Cu) content, even with the reduction of surface area and metal dispersion. However, this behavior occurred only up to catalyst A4. For the catalyst A5, which had the highest amount of copper, the conversion was the lowest found, that is, the effect of drastic reduction of the metal dispersion was greater than the effect of the Cu percentage, and the dispersion became the activity controller. The commercial catalyst showed the highest conversion due to its combination of high active phase content and high specific area. One explanation for the fact that no sol-gel catalyst was more active than the commercial is that the sol-gel method produces extremely homogeneous materials, namely, the active phase is not distributed only on the surface available for reaction, but also in support matrix (alumina), where is inaccessible to the reactants. In contrast, the sol-gel synthesis tends to produce highly porous materials with specific areas larger than those produced by more traditional methods. The catalysts A1 and A2 showed the highest Turnover Frequency (TOF). In a matter of catalytic activity by active site, the TOF decreased with increasing the amount of Cu. This is because, for smaller quantities of copper, it is more dispersed on the catalyst surface, and the active sites become more available for reaction. Thus, the catalyst A1 showed the highest conversion by active phase amount, due to its better dispersion and higher specific area. In conclusion, it was found that the catalyst A1 had the highest metal dispersion and the better reaction frequency (TOF), and that the HiFUEL R120 produced the highest conversion, followed by the A4 sol-gel, which proved to be the most active sol-gel catalyst.