Aproveitamento de CO2 para a produção de metanol e compostos C2+ aplicando catalisadores à base de Cu e Fe

Abstract

Considering the approaches to use of the CO2, this work aimed to study CO2 hydrogenation at gas phase and CO2 reduction (CO2RR) via electrocatalysis. Through these methodologies a wide variety of value-added products can be obtained, such as methanol and compounds with two or more carbon atoms (C2+). In a first stage of this work, Cu and Fe-based materials were investigated in the CO2 hydrogenation reaction. The production of methanol on Cu/Zn materials was influenced by the presence of promoters (Al, Cr, Ga, Nb, and Zr). The content, incorporation method to Cu/Zn, and chemical nature of the investigated promoters had a direct influence on the selectivity to CH3OH or CO. Cu50/Zn45/Nb5, prepared by co-precipitation, was the catalyst that showed the best activity and selectivity to methanol, because of its physical-chemical characteristics. Through spectroscopic investigations, intermediates of methanol synthesis were identified, and it was verified that CO adsorbs stably on Cu50/Zn45/Nb5, which contributes to the formation of methanol at the expense of CO. By applying Fe-Cu-Al-K to the CO2 hydrogenation reaction, CO, CH4 and C2+ hydrocarbons were obtained as products. The C-C coupling was favored when the material was reduced at 300 °C and exposed to higher reaction temperatures in range investigated here. In a second stage of this work, the combination of Cu50/Zn45/Nb5 and Fe-Cu-Al-K was evaluated by physical mixing and by overlapping beds of these materials. The formation of C2+ alcohols (C2+OH) was verified, attesting the complementation of the hydroxyl group formation (Cu50/Zn45/Nb5) and the carbon chain propagation (Fe-Cu-Al-K) functions. A statistical chemometrics optimization procedure was used to determine, among the investigated variables, the most favorable conditions for the C2+OH production. The model was experimentally validated and proved to be adequate. By DRIFTS, intermediates of the C2+OH formation on the 50%m Cu50/Zn45/Nb5 and 50%m Fe-Cu-Al-K physical mixture were identified. Finally, in the third and last stage of this work, the CO2RR was investigated on copper catalysts. Cu nanoparticles were more selective to the production of C2+ compounds, such as ethanol and ethylene, when compared to the smooth copper surface. Contrasting results of the CO2 hydrogenation and CO2RR on Cu and Cu/Zn-based materials, it was clear that the reaction environment has a significant influence on the products distribution.