Hidróxidos duplos lamelares (HDL) à base de cobre para produção de hidrogênio e outros produtos de valor agregado
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Data
2020-04-08
Autores
Santos, Rodrigo Morais Menezes dos
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Universidade Estadual Paulista (Unesp)
Resumo
Atualmente, os problemas associados ao uso de combustíveis fósseis têm sido um tema de grande preocupação, gerando interesse em processos baseados no uso de energia limpa e renovável. O etanol produzido de fontes renováveis vem se mostrando vantajoso em vários aspectos e promissor na substituição e/ou complementação da petroquímica no futuro, na obtenção de diversos produtos de valor agregado. Os hidróxidos duplos lamelares (HDL) e seus derivados têm recebido muita atenção nas últimas décadas devido a importantes aplicações, particularmente em catálise, com vantagens relacionadas à uniforme distribuição dos cátions metálicos em sua estrutura, a nível atômico, além da flexibilidade de composições. Além disso, quando submetidos a um tratamento térmico, os HDL dão origem a nanopartículas metálicas estáveis e altamente dispersas em uma matriz de óxido misto com forte interação metal-suporte. Neste trabalho foram sintetizados catalisadores derivados de CuZnAl-HDL contendo 0, 5, 10 e 20% m/m de cobre, avaliando suas características e sua eficiência na reação de desidrogenação do etanol (EDR). Os catalisadores foram analisados por um conjunto de técnicas, com destaque para a caracterização por quick-XAS das espécies de Cu e Zn envolvidas nas etapas de formação do catalisador e reação em condições operando. Por meio do uso de ferramentas quimiométricas, como MCR-ALS no tratamento dos conjuntos de dados, foi observado que o teor de cobre no catalisador influencia na composição das fases presentes no suporte, fornecendo diferentes composições de nanoZnO, nano-ZnAl2O4 e um intermediário identificado como pré-núcleo tetraédrico (TPN) de zinco. Por sua vez, a composição do suporte, modifica as propriedades texturais dos catalisadores e, sobretudo o tamanho de nanopartículas e dispersão da fase ativa, relacionados com a atividade dos catalisadores. Estudando diferentes rotas de ativação, foi observada uma maior atividade relacionada a uma mistura de espécies Cu+:Cu0 em relação às espécies de Cu0, mas com alta instabilidade das espécies de Cu+ em condições de maiores conversões (temperaturas e teores de cobre mais altos). Adicionalmente, os resultados mostram a importância do suporte na dispersão da fase ativa e estabilidade, em que o uso de precursor de HDL mostrou interessantes propriedades a serem aplicadas em uma ampla variedade de reações catalíticas.
Nowadays, the problems associated with the use of fossil fuels have been a topic of great concern, generating interest in processes based on the use of clean and renewable energy. Ethanol produced from renewable sources has proved to be advantageous in several aspects and promising in the replacement and/or complementation of the petrochemistry in the future, in obtaining several value-added products. Layered double hydroxides (LDH) and their derivatives have received much attention in the past decades due to important applications, particularly in catalysis, with advantages related to the uniform distribution of metallic cations in their structure, at the atomic level, in addition to the flexibility of compositions. Furthermore, when subjected to a thermal decomposition, LDH give rise to stable and highly dispersed metallic nanoparticles in a mixed oxide matrix, showing strong metal-support interaction. In this work, catalysts derived from CuZnAl-LDH containing 0, 5, 10 and 20% wt. copper were synthesized, evaluating their characteristics and their efficiency in the ethanol dehydrogenation reaction (EDR). The catalysts were analyzed by a set of techniques, with emphasis on the characterization by quick-XAS of the Cu and Zn species involved in the stages of formation of the catalyst and reaction under operando conditions. Through the use of chemometric tools, such as MCR-ALS in the treatment of datasets, it was observed that the copper content in the catalyst influences the phase composition in the support, providing different compositions of nano-ZnO, nano-ZnAl2O4 and an intermediate, identified as a tetrahedral pre-nucleus (TPN) of zinc. On the other hand, the support composition modifies the textural properties of the catalysts and, especially the nanoparticle sizes and dispersion of the active phase, related to the activity of the catalysts. Studying different activation routes, it was observed a greater activity related to a mixture of Cu+ :Cu0 species in relation to Cu0 species but with high instability of Cu+ species in conditions of greater conversions (at higher temperatures and copper contents). Additionally, the results show the importance of support in the dispersion of the active phase and stability, in which the use of LDH precursors showed interesting properties to be applied in a wide variety of catalytic reactions.
Nowadays, the problems associated with the use of fossil fuels have been a topic of great concern, generating interest in processes based on the use of clean and renewable energy. Ethanol produced from renewable sources has proved to be advantageous in several aspects and promising in the replacement and/or complementation of the petrochemistry in the future, in obtaining several value-added products. Layered double hydroxides (LDH) and their derivatives have received much attention in the past decades due to important applications, particularly in catalysis, with advantages related to the uniform distribution of metallic cations in their structure, at the atomic level, in addition to the flexibility of compositions. Furthermore, when subjected to a thermal decomposition, LDH give rise to stable and highly dispersed metallic nanoparticles in a mixed oxide matrix, showing strong metal-support interaction. In this work, catalysts derived from CuZnAl-LDH containing 0, 5, 10 and 20% wt. copper were synthesized, evaluating their characteristics and their efficiency in the ethanol dehydrogenation reaction (EDR). The catalysts were analyzed by a set of techniques, with emphasis on the characterization by quick-XAS of the Cu and Zn species involved in the stages of formation of the catalyst and reaction under operando conditions. Through the use of chemometric tools, such as MCR-ALS in the treatment of datasets, it was observed that the copper content in the catalyst influences the phase composition in the support, providing different compositions of nano-ZnO, nano-ZnAl2O4 and an intermediate, identified as a tetrahedral pre-nucleus (TPN) of zinc. On the other hand, the support composition modifies the textural properties of the catalysts and, especially the nanoparticle sizes and dispersion of the active phase, related to the activity of the catalysts. Studying different activation routes, it was observed a greater activity related to a mixture of Cu+ :Cu0 species in relation to Cu0 species but with high instability of Cu+ species in conditions of greater conversions (at higher temperatures and copper contents). Additionally, the results show the importance of support in the dispersion of the active phase and stability, in which the use of LDH precursors showed interesting properties to be applied in a wide variety of catalytic reactions.
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Hidróxidos duplos lamelares (HDL), Nanopartículas de cobre, Óxidos mistos, Catalisadores metálicos suportados, Catálise heterogênea, Desidrogenação do etanol (EDR)