Reações de valorização do glicerol utilizando sílica mesoporosa modificada com vanádio
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Data
2019-03-29
Autores
Abreu, Thiago Holanda de [UNESP]
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
SiMCM-41 e V-MCM-41 foram sintetizados por via hidrotérmica com diferentes quantidades de vanádio. As caracterizações foram realizadas por Espalhamento de raios X a ângulo pequeno (SAXS), Fisissorção de nitrogênio, Ressonância magnética nuclear de 29Si (RMN), Microscopia eletrônica de transmissão (MET) e Termogravimetria (TG). A acidez dos materiais foi avaliada por dessorção de amônia à temperatura programada (TPD-NH3) e Quimissorção de piridina seguida por espectroscopia vibracional na região de infravermelho. As espécies de vanádio foram avaliadas por Espectroscopia no ultravioleta (UV), Espectroscopia de fotoelétrons excitados por raios X (XPS) e redução à temperatura programada em hidrogênio (TPR-H2). Os materiais à base de vanádio são classicamente utilizados em reações de oxidação, porém apresentam também sítios ácidos que podem ser utilizados em reações de desidratação. Neste trabalho, vanadossilicatos mesoporosos foram utilizados como catalisadores ácidos na cetalização do glicerol com acetona para formação de solketal. A atividade catalítica se mostra dependente da quantidade de sítios ácidos, baseada em três tipos de espécies de óxido de vanádio verificadas nas caracterizações realizadas: (i) espécies de vanádio isoladas (ii) oligoméricas inseridas na estrutura de sílica, isto é, O-(V-O-V)n, em que n = 1 e n> 1, respectivamente (iii) óxidos de vanádio superficiais altamente dispersos ou interagindo com grupos hidroxila de superfície. Ao realizar experimentos de reuso, foi possível concluir que as espécies de óxidos de vanádio na superfície, apesar de serem mais ativas, são lixiviadas por moléculas de água formadas na reação, diminuindo a atividade. Os mesmos materiais foram utilizados para a reação de desidratação oxidativa do glicerol. Nesta reação, as espécies de vanádio possuem uma dupla função, exercendo papel de sítio ácido e redox. A atividade catalítica foi dependente dos tipos de espécies de vanádio na superfície do catalisador. Foi observado também, que após 6 h de reação, o catalisador continuou convertendo glicerol. Contudo, a seletividade a ácido acrílico caiu drasticamente, levando à formação de CO e CO2, devido à hidratação, que consequentemente, alterou os sítios de vanádio. A SiMCM-41 também foi impregnada com o sal acetil acetonato de vanádio sem colapsar sua estrutura.
SiMCM-41 and V-MCM-41 were synthesized by hydrothermal synthesis with different amounts of vanadium. The characterization wasperformed by Small angle X ray scattering (SAXS), Nitrogen Fisissortion, 29Si Nuclear Magnetic Resonance (NMR), Transmission Electron Microscopy (TEM) and Thermogravimetry (TG). The acidity of the materials was evaluated by temperature-programed desorption of ammonia (TPD-NH3) and Quimissortion of pyridine followed by infrared spectroscopy. Vanadium species were evaluated by Ultraviolet Spectroscopy (UV), Spectroscopy of X-ray excited photoelectrons (XPS) and H2 temperature-programed reduction(TPR-H2). Vanadium-based materials are classically usedin oxidation reactions, but also have acidic sites that can be used in dehydration reactions. In this work, mesoporous vanadosilicates were used as acid catalysts in the ketalization of glycerol with acetone to form solketal. The catalytic activity was dependent on the amount of acid sites, based on three types of vanadium oxide species found in the characterizations performed: (i) isolated vanadium species (ii) oligomeric species inserted into the silica structure, O-(V-O-V)n, where n = 1 and n> 1, respectively(iii) highly dispersed surface vanadium oxides or interacting with surface hydroxyl groups. When conducting reuse experiments, it was possible to conclude that the vanadium oxide species on the surface, although more active, are leached by water molecules formed from the reaction, reducing the activity. The same materials were used for the oxidative dehydration reaction of glycerol. In this reaction the vanadium species have a double function, acid and redox site. The catalytic activity was dependenton the types of vanadium species on the catalyst surface. It was also observed that after 6hourof reaction the catalyst continues to convert glycerol, however the selectivity to Acrylic acid drops dramatically, leading to the formation of CO and CO2, due to hydration and consequently change in the vanadium sites. SiMCM-41 was also impregnated with the vanadium acetyl acetonate salt without collapsing structure.
SiMCM-41 and V-MCM-41 were synthesized by hydrothermal synthesis with different amounts of vanadium. The characterization wasperformed by Small angle X ray scattering (SAXS), Nitrogen Fisissortion, 29Si Nuclear Magnetic Resonance (NMR), Transmission Electron Microscopy (TEM) and Thermogravimetry (TG). The acidity of the materials was evaluated by temperature-programed desorption of ammonia (TPD-NH3) and Quimissortion of pyridine followed by infrared spectroscopy. Vanadium species were evaluated by Ultraviolet Spectroscopy (UV), Spectroscopy of X-ray excited photoelectrons (XPS) and H2 temperature-programed reduction(TPR-H2). Vanadium-based materials are classically usedin oxidation reactions, but also have acidic sites that can be used in dehydration reactions. In this work, mesoporous vanadosilicates were used as acid catalysts in the ketalization of glycerol with acetone to form solketal. The catalytic activity was dependent on the amount of acid sites, based on three types of vanadium oxide species found in the characterizations performed: (i) isolated vanadium species (ii) oligomeric species inserted into the silica structure, O-(V-O-V)n, where n = 1 and n> 1, respectively(iii) highly dispersed surface vanadium oxides or interacting with surface hydroxyl groups. When conducting reuse experiments, it was possible to conclude that the vanadium oxide species on the surface, although more active, are leached by water molecules formed from the reaction, reducing the activity. The same materials were used for the oxidative dehydration reaction of glycerol. In this reaction the vanadium species have a double function, acid and redox site. The catalytic activity was dependenton the types of vanadium species on the catalyst surface. It was also observed that after 6hourof reaction the catalyst continues to convert glycerol, however the selectivity to Acrylic acid drops dramatically, leading to the formation of CO and CO2, due to hydration and consequently change in the vanadium sites. SiMCM-41 was also impregnated with the vanadium acetyl acetonate salt without collapsing structure.
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Palavras-chave
MCM-41, Vanádio, Glicerol, Solketal, Ácido acrílico