Estudo da reação de hidrogenação de CO2 em materiais à base de Cu via catálise heterogênea

Abstract

CO2 is a greenhouse gas whose production has intensified in recent decades, generating its accumulation in the Earth’s atmosphere. Thereby, numerous negative environmental changes, such as the aggravation of the greenhouse effect, have occurred all over the planet. Mitigating approaches have been adopted in several countries around the world, such as the capture and storage of CO2 and the use of renewable energy sources instead of fossil sources. Furthermore, the use of this gas as a carbonaceous input for the production of chemical compounds with high added value is a promising alternative. In this regard, the catalytic hydrogenation of CO2 is a carbon recycling technology that has been explored in recent years. This reaction can occur via electro-catalysis and heterogeneous catalysis at gas-phase. In the present work only the catalytic process at gas-phase will be focused. In this process H2 is used as a hydrogen source and the application of Cu-based catalysts promotes mainly the formation of C1 compounds, such as CO and methanol. These reactions typically occur at temperatures of 200 – 300 °C and under pressures of 2 – 7 MPa. Thus, the investigation of more favorable conditions for the hydrogenation of CO2 at gas-phase on non-noble metals-based materials, such as copper, for the efficient and selective production of high energy density compounds, such as ethanol, ethylene, propane and butanol, is necessary. Recently, in our research group, catalytic studies of CO2 hydrogenation on copper, conducted at gas-phase in the presence of water steam under atmospheric pressure, led to the formation of ethanol. There are evidences that water acts in the stabilization of adsorbed intermediates of the reaction, such as CO, favoring the formation of ethanol. However, the impact of the catalyst properties in this reaction has been poorly explored. In this context, the objective of this work is to study the influence of the copper oxidation state on the CO2 hydrogenation reaction at gas phase in the presence and absence of water steam on Cu materials, aiming at the production of alcohols with two or more carbon atoms (C2+OH). Results of this work showed that ethanol production is more pronounced when we used water steam as a hydrogen source and catalysts with a mixture of oxidized and metallic copper species. Furthermore, it was observed that the presence of oxidized copper species together with metallic copper species was important to improve the productivity of methanol, in addition to ethanol, when H2 was applied as a hydrogen source, indicating the importance of having different copper species to intensify the production of alcohols.