Navegando por Autor "Lopes, Osmando Ferreira"
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Item Acidic surface niobium pentoxide is catalytic active for CO2 photoreduction.(2019) Silva, Gelson Tiago dos Santos Tavares da; Nogueira, André Esteves; Oliveira, Jessica Ariane de; Torres, Juliana Arriel; Lopes, Osmando Ferreira; Oliveira, Cauê Ribeiro deIn this paper, we report for the first time the significant photocatalytic activity of Nb-based materials for CO2 reduction. Nb2O5 catalysts were prepared through a modified peroxide sol-gel method using different annealing temperatures, showing activity for CO2 photoreduction in all conditions. The activity and selectivity of the Nb2O5 samples were directly related to their surface acidity: high surface acidity prompted conversion of CO2 to CO, HCOOH, and CH3COOH; low surface acidity prompted conversion of CO2 to CH4. The results also indicated that CO is the main intermediate species of the CO2 photoreduction in all conditions. We have uncovered the role played by the surface acidity of Nb2O5 and the mechanism behind its performance for CO2 photoreduction.Item CuO decoration controls Nb2O5 photocatalyst selectivity in CO2 reduction.(2020) Nogueira, André Esteves; Silva, Gelson Tiago dos Santos Tavares da; Oliveira, Jessica Ariane de; Lopes, Osmando Ferreira; Torres, Juliana Arriel; Carmo, Marcelo; Oliveira, Cauê Ribeiro deThe reformation of CO2 through photocatalytic processes to obtain products with high energy value and compatibility with the current energy infrastructure is a compelling strategy to minimize the emission of CO2 into the atmosphere, one of the main greenhouse gases. However, practical application of such a photocatalytic system requires significant efforts for improved CO2 photoreduction performance and product selectivity. Thus, in the present work, CuO nanoparticles were combined with Nb2O5 in order to improve the photocatalytic properties of these semiconductors in the CO2 photoreduction process. Nb2O5/ CuO heterojunctions were prepared via a solvothermal treatment method, while the experimental tools, such as FESEM, HRTEM, and DRS, were employed to evaluate the microstructural and electronic properties. We describe how CuO decoration over Nb2O5 adjusts its selectivity for CO2 reduction to CH4, HCOOH, or H3CCOOH in different contents. An investigation of CO2 photoreduction using different electron donors/scavengers (water, sodium oxalate, and potassium bromate) under ultraviolet radiation revealed that its decoration influences local CO production by modifying the selectivity. CO has been confirmed as the main intermediate for HCOOH and CH3COOH production, and CO2 reduction efficiency increases at low CuO content (2.5% wt), leading to the formation of soluble hydrocarbons, and increases for CH4 in higher amounts (10% wt).Item Enhancing TiO2 activity for CO2 photoreduction through MgO decoration.(2020) Torres, Juliana Arriel; Nogueira, André Esteves; Silva, Gelson Tiago dos Santos Tavares da; Lopes, Osmando Ferreira; Wang, Yanjie; He, Tao; Oliveira, Cauê Ribeiro deHerein we report on the influence of MgO’s basic character in the photoactivity of MgO:TiO2 nanocomposites for the CO2 reduction reaction. TiO2 nanoparticles, decorated with MgO in different mass proportions, were synthesized by the physical mixing of pre-synthesized oxides followed by calcination. The decorated samples presented enhanced photocatalytic activity with higher selectivity for CO, while CH4 was also produced, as well as HCOOH and CH3COOH in a liquid medium in lower proportions. The results indicate that the beneficial MgO influence is only effective at low amounts, whilst a high MgO amount favors an insulating behavior instead of semiconducting, reducing the nanocomposite performance for CO2 photoreduction.Item Redução de CO2 em hidrocarbonetos e oxigenados : fundamentos, estratégias e desafios.(2021) Silva, Gelson Tiago dos Santos Tavares da; Lopes, Osmando Ferreira; Dias, Eduardo Henrique; Torres, Juliana Arriel; Nogueira, André Esteves; Faustino, Leandro Augusto; Prado, Fernando Siqueira; Patrocinio, Antonio Otavio de Toledo; Oliveira, Cauê Ribeiro deThe development of renewable energy sources (e.g., solar and wind) moves foward, the tendance for replacing fossil fuels increases. However, these technologies have as primary barriers to industrial processes’ efficiency and especially storage. Thus, CO2 reduction routes using these energy sources could chemically store part of the energy as fuels or chemicals, offering alternatives to current oil and gas industry. This process is inspired by photosynthesis, e.g., photochemical or electrochemical processes, using homogeneous or heterogeneous catalysts. Nevertheless, this reaction is thermodynamically unfavorable and has very slow kinetics, given the high stability of the CO2 molecule and the complexity of the redox reactions involved. Therefore, this review addresses this process’s kinetic and thermodynamic challenges, and the fundamental concepts of the photo(electro)chemical processes for CO2 reduction, besides presenting and discussing the materials with the potential to act as catalysts. The main reaction mechanisms and advances in the understanding of such processes are discussed, as well as future perspectives.