Descri??o te?rica da rea??o de redu??o na reforma a vapor via ciclos qu?micos

• Ano de defesa: 2019
• Autor(a) principal: Fernandes, Felipe Marinho
• Orientador(a): Silva, Clarissa Oliveira da
• Banca de defesa: Pereira, Marcio Soares, Rodrigues, Victor de Oliveira, Silva J?nior, Ant?nio Marques da
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal Rural do Rio de Janeiro
• Programa de Pós-Graduação: Programa de P?s-Gradua??o em Qu?mica
• Departamento: Instituto de Qu?mica
• País: Brasil
• Palavras-chave em Português: Reforma Catal?tica; ?xido de Ferro; DFT; Multiplicidade
• Palavras-chave em Inglês: Catalytic Reform; Iron Oxide; Multiplicity
• Área do conhecimento CNPq: Qu?mica
• Link de acesso: https://tede.ufrrj.br/jspui/handle/jspui/5428

The world energy matrix is mostly dependent on petroleum-based fuels. However, this pattern leads to several negative impacts mainly on the Earth's atmosphere. In addition, it is well known that, following the current rate of oil consumption, human kind might run out of these sources in less than 50 years. Therefore, the adoption of a sustainable energy matrix is fundamental for the future. Hydrogen is an excellent candidate to take over the current energy matrix. When burned, it produces water as a product (considerably less harmful than the products of combustion of fossil fuels), and in car engines, for example, it?s up to three times more efficient than gasoline. There are a few ways, however, to produce hydrogen. The most usual, nowadays, are steam reform processes. However, there is a process that has been revisited: steam reforming through chemical cycles. Due to nanotechnology, iron oxide-based nanocatalysts were made possible again by increasing the resistance of these important participants in the reactions involved in the process and thus making possible this method of hydrogen production. So, we will approach with a theoretical bias the reduction stage of the magnetite (chosen catalyst) in the steam reforming through chemical cycles: CH4 + 4Fe3O4 ? CO2 + H2O + 12FeO. We approached magnetite, which is a mineral, solid at room temperature and pressure and this solid has minimal formula as Fe3O4. The magnetite has been approximated to a cluster structure, which is a set of atoms representing the solid structure, Fe12O16. Due to the magnetic properties of the mineral, the reaction steps have been studied in three different electronic state levels: singlet, triplet and quintet. So far, triplet multiplicity has been observed as the ground state of the cluster study conducted that considered from one Fe3O4 unit to four units, where the triplet difference for singlet and quintet was at least 94 kcal/mole for cluster with BPW91 functional and dual polarized LAV2P base (BPW91 / LAV2P **). The largest cluster, Fe12O16, was also adopted as cluster in chemical reaction steps. The results on the singlet, triplet and quintet multiplicity were evaluated and a physical adsorption channel was proposed with four singlet products and five products in both triplet and quintet. The removal of one hydrogen from the methane to give continuity to the chemical reaction generating products of chemisorption was evaluated in these three multiplicities. Two chemisorption products were located in singlet and also in triplet. But only one product was found in quintet. Proposals for transition states were also suggested in this work as an attempt to connect the steps of physisorption and chemisorption. For singlet, the Down_H_O channel had a binding barrier of approximately 90 kcal/mole and Up_H_Otetra presented a barrier of approximately 45 kcal/mole. In triplet, the barriers found were approximately 20 kcal/mole and 60 kcal/mole for the channels Up_H_Oocta and Up_H_Otetra respectively. In quintet, only one channel was found and the barrier, Up_H_Oocta, was around 65 kcal/mole.