Funcionalização da superfície de catalisadores zeolíticos para uso na reação de Knoevenagel
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Data
2023-01-12
Autores
Pataca, Iara de Lacerda
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
Devido ao contexto atual ambiental, há uma grande demanda de procedimentos que
substituam a utilização de catalisadores homogêneos e principalmente solventes
orgânicos, por materiais com menor impacto ambiental. Visando suprir essas
necessidades, a utilização de catalisadores heterogêneos ácidos vem tendo cada vez
mais relevância em processos químicos, tais como no craqueamento e refinamento
de petróleo. Mesmo apresentando grande potencial, catalisadores heterogêneos
básicos ainda não têm tantas aplicações como os ácidos, por esse motivo, esse
projeto propõe o desenvolvimento de catalisadores básicos para avaliação de sua
atividade catalítica na reação de condensação de Knoevenagel. Essa reação é muito
utilizada para a produção de intermediários químicos durante a produção de
cosméticos, e normalmente se processa com a utilização de solventes orgânicos a
altas temperaturas para melhorar o rendimento da reação. Dessa forma, faujasitas de
razões Si/Al (1,4 e 2,5) foram funcionalizadas com organosilanos de cadeias
carbônicas diferentes (C8 e C12), para aumentar a hidrofobicidade da estrutura e
melhorar o rendimento do catalisador. A partir disso, algumas técnicas como
termogravimetria, difração de raios-X, CHN(O)S, XPS e fisissorção de N2 foram
aplicadas para caracterizar os catalisadores, comprovando a eficiência da
funcionalização e o aumento na basicidade dos materiais com a conservação da sua
estrutura cristalina. Também foram feitas medidas do ângulo de contato com glicerol,
o que mostrou alterações nas hidrofobicidade dos materiais. Analisando os resultados
foi possível observar que as funcionalizações com organosilanos do tipo C8 foram
mais eficientes, além das amostras apresentaram maior hidrofobicidade e basicidade
que as funcionalizadas com C12, o que provavelmente se deve ao impedimento
estérico de uma cadeia maior. Foram feitos testes catalíticos para a reação de
Knoevenagel, que comprovaram um aumento significativo da conversão em FAUs
com C8, principalmente a FAU 2,5 que teve aumento de aproximadamente 17%,
comprovando a influência positiva desse tipo de alteração química em zeólitas
básicas.
Nowadays, there is a great demand for techniques that substitute the need of homogeneous catalysts, mainly organic solvents, for materials with less environmental impact. In order to supply these needs, acid heterogeneous catalysts have been having an increasing relevance in chemical processes, such as the cracking and refining of petroleum. Even though having great potential, basic heterogeneous catalysts have not had the same applications as the acid ones, for this reason, this project proposes the development of basic catalysts, for the evaluation of their catalytic activity when applied to Knoevenagel condensation reactions. This reaction is largely used for the production of chemical intermediates during the production of cosmetics and is processed in the presence of organic solvents at high temperatures, to improve the reaction’s yields. That way, faujasites with Si/Al ratios (1,4 and 2,5) were functionalized with organosilanes of different carbonic chains (C8 and C12), to improve the hydrophobicity of the structure and the yield of the catalyst, eliminating the use of solvents. After that, characterization techniques such as thermogravimetry, X-Ray Diffraction, CHN(O)S, XPS and Nitrogen physisorption were used to verify the efficiency of the functionalization and increase in basicity of the materials, while maintaining its crystallinity. Measurements of the contact angle with glycerol were also performed, attesting to the increase in hydrophobicity of the samples, mainly the ones functionalized with C8, which presented the biggest efficiency during the functionalization, according to the results from the techniques. After that, catalysis efficiency tests were made for the Knoevenagel reactions, showing that the samples with C8 had an increase of 17% in conversion when compared to the pure zeolites, validating the bigger basicity of the catalysts.
Nowadays, there is a great demand for techniques that substitute the need of homogeneous catalysts, mainly organic solvents, for materials with less environmental impact. In order to supply these needs, acid heterogeneous catalysts have been having an increasing relevance in chemical processes, such as the cracking and refining of petroleum. Even though having great potential, basic heterogeneous catalysts have not had the same applications as the acid ones, for this reason, this project proposes the development of basic catalysts, for the evaluation of their catalytic activity when applied to Knoevenagel condensation reactions. This reaction is largely used for the production of chemical intermediates during the production of cosmetics and is processed in the presence of organic solvents at high temperatures, to improve the reaction’s yields. That way, faujasites with Si/Al ratios (1,4 and 2,5) were functionalized with organosilanes of different carbonic chains (C8 and C12), to improve the hydrophobicity of the structure and the yield of the catalyst, eliminating the use of solvents. After that, characterization techniques such as thermogravimetry, X-Ray Diffraction, CHN(O)S, XPS and Nitrogen physisorption were used to verify the efficiency of the functionalization and increase in basicity of the materials, while maintaining its crystallinity. Measurements of the contact angle with glycerol were also performed, attesting to the increase in hydrophobicity of the samples, mainly the ones functionalized with C8, which presented the biggest efficiency during the functionalization, according to the results from the techniques. After that, catalysis efficiency tests were made for the Knoevenagel reactions, showing that the samples with C8 had an increase of 17% in conversion when compared to the pure zeolites, validating the bigger basicity of the catalysts.
Descrição
Palavras-chave
Catálise heterogênea, Zeólita faujasita, Funcionalização, Catalisadores básicos, Reação de Knoevenagel