Navegando por Autor "Ribeiro, Leandro Passos"
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Item Catalytic carbon deposition-oxidation over Ni, Fe and Co catalysts : a new indirect route to store and transport gas hydrocarbon fuels.(2013) Oliveira, Patrícia E. F.; Ribeiro, Leandro Passos; Rosmaninho, Marcelo Gonçalves; Ardisson, José Domingos; Dias, Anderson; Oliveira, Luiz Carlos Alves de; Lago, Rochel MonteroIn this work, a new two-step route to store and transport associated natural gas, promoted by Ni, Fe and Co supported catalyst was presented. Initially, CH4 is converted into carbon deposits (M/C composite), being Fe catalyst the most active catalyst. In Step 2, M/C composite reacts with H2O producing H2, CO and CH4. TPO experiments showed that efficiency and selectivity of oxidation depends on the metal. Ni catalyst produced mainly H2 and CO, while Fe system was more selective to convert carbon into CH4. The formation of C2 and C3 compounds suggests the presence of a Fischer Tropsch like process.Item Effect of Sn on methane decomposition over Fe supported catalysts to produce carbon.(2011) Freitas, Patrícia Elizabeth de; Ribeiro, Leandro Passos; Rosmaninho, Marcelo Gonçalves; Ardisson, José Domingos; Dias, Anderson; Lago, Rochel MonteroIn this work, alumina-supported Sn containing Fe catalysts were investigated in CVD reactions (Chemical Vapor Deposition) using methane for carbon production. The catalysts were prepared with 10 wt.% of Fe (as Fe2O3) and 3, 6 and 12 wt.% of Sn (as SnO2) supported on Al2O3 named hereon Fe10Sn3A, Fe5Sn6A and Fe10Sn12A, respectively. These catalysts were characterized by SEM, TPCVD, TPR, TG, Raman,XRDand 57Fe and 119Sn Mössbauer spectroscopy.Methane reacts with Fe10A catalyst (without Sn) in the temperature range 680–900◦C to produce mainly Fe0, Fe3 C and 20 wt.% of carbon deposition. TPR and TPCVD clearly showed that Sn strongly hinders the CH4 reaction over Fe catalyst. 57Fe Mössbauer suggested that in the presence of Sn the reduction of Fe+3 by methane becomes very difficult. 119Sn Mössbauer showed Sn+4 species strongly interact with metallic iron after CVD, producing iron-tin phases such as Fe3SnC and FeSn2. This interaction Sn–Fe increases the CVD temperatures and decreases the carbon yield leading to the production of more organized forms of carbon such as carbon nanotubes, nanofibers and graphite.Item Magnetic amphiphilic composites based on carbon nanotubes and nanofibers grown on an inorganic matrix : effect on water-oil interfaces.(2010) Oliveira, Aline A. S.; Teixeira, Ivo Freitas; Ribeiro, Leandro Passos; Tristão, Juliana Cristina; Dias, Anderson; Lago, Rochel MonteroNovos compósitos magnéticos anfifílicos foram preparados pelo crescimento de nanotubos e nanofibras de carbono contendo partículas magnéticas através de deposição química de vapor (CVD), utilizando etanol como fonte de carbono e lama vermelha (RM, subproduto do processo Bayer de produção de alumina) como suporte e catalisador. Monitoramento da reação CVD à temperatura programada (TPCVD), difração de raios X (XRD), espectroscopia Mössbauer, espectroscopia de energia dispersiva (EDS), espectroscopia Raman, termogravimetria (TG/DTA), análise elementar (CHN), determinação de área superficial (BET), microscopia eletrônica de varredura (SEM) e de transmissão (TEM) e medidas magnéticas mostraram que etanol reduz íons de ferro na RM para formar fases magnéticas, por exemplo Fe3O4 e Fe0, e depósitos de carbono (5-42 wt.%) na forma de nanotubos e nanofibras. A combinação de nanoestruturas hidrofóbicas de carbono com óxidos hidrofílicos de Al, Si e Ti presentes na lama vermelha produziu materiais anfifílicos com excelente interação com a interface água-óleo. Misturas de óleo de soja ou de decalina com água (completamente imiscíveis) foram emulsificadas facilmente na presença dos compósitos anfifílicos. Quando os compósitos foram adicionados a uma emulsão água-biodiesel estável, as partículas anfifílicas difundiram-se para a interface água- óleo. As partículas do compósito foram atraídas por ímãs e carregaram com elas as gotas de óleo, levando à completa desemulsificação e separação entre biodiesel e água.