Catalizadores bimetálicos de Ni-Cu soportados en biochar y su efecto en la hidrogenación de compuestos de interés farmacéutico.
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Date
2025
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Publisher
Universidad de Concepción
Abstract
La hidrogenación catalítica en fase líquida del nitrobenceno constituye el método principal para la síntesis de anilina, precursor clave en la industria farmacéutica. Esta reacción ocurre mediante la reducción del grupo nitro en presencia de un agente reductor como el H2 y un catalizador óptimo para la activación de ambos reactivos. Entre las alternativas más efectivas y económicas frente a los metales nobles destacan los catalizadores de metales no-nobles soportados, como el níquel. Para promover su desempeño catalítico, se ha propuesto la formación de una aleación bimetálica, donde se potencian las propiedades y actividad del metal principal.
Este estudio se enfoca en evaluar el efecto de la razón Cu/Ni en las propiedades fisicoquímicas de los catalizadores bimetálicos y en el rendimiento catalítico de la reacción de hidrogenación. Se sintetizaron nanopartículas de NiCux (x = 0.1, 0.2, 0.3) soportadas en biochar mediante impregnación húmeda seguida de pirólisis, reducción y pasivación, según corresponda. Las propiedades de los catalizadores se caracterizaron mediante TEM, SEM-EDS, TPR-H2, AAS, TGA-MS, FTIR, XRD y Adsorción/desorción de N2. El efecto de los procesos térmicos en los parámetros de conversión y selectividad también fue evaluado. La reacción se llevó a cabo en un reactor batch a 130°C, 20 bar H2, 700 rpm, por 6 horas.
Los resultados evidencian que introducir cobre reduce el tamaño de las nanopartículas y contribuye a aumentar la dispersión de éstas en superficie. Sin embargo, mediante TEM, se observaron zonas de aglomeración sobre el soporte, atribuido a la dificultad de las partículas metálicas de ingresar a las porosidades debido a su gran tamaño. Mediante XRD y SEM-EDS se confirmó la formación de la aleación Ni-Cu, mientras que el análisis TGA-MS indicó que durante la reducción, el biochar sufrió descomposición y metanación, catalizada por la presencia de Ni.
Los resultados de reacción muestran que la secuencia de pirólisis y reducción es la indicada para asegurar la presencia de sitios activos. No obstante, los catalizadores bimetálicos NiCux presentaron menores conversiones en comparación con el mono metálico, independiente del tratamiento térmico aplicado. Por tanto, la estructura bimetálica soportada en biochar no es adecuada para la hidrogenación de nitrobenceno. Se propone que las propiedades fisicoquímicas y la inestabilidad estructural del soporte además de la interacción metal/biochar, inhiben el efecto cooperativo de la aleación Ni-Cu formada, perjudicando la conversión de nitrobenceno a anilina.
The catalytic liquid-phase hydrogenation of nitrobenzene is the main method for the synthesis of aniline, a key precursor in the pharmaceutical industry. This reaction occurs through the reduction of the nitro group in the presence of a reducing agent such as H2 and an optimal catalyst for the activation of both reagents. Among the most effective and economical alternatives to noble metals are supported non-noble metal catalysts such as nickel. To promote their catalytic performance, the formation of a bimetallic alloy has been proposed, where the properties and activity of the main metal are enhanced. This study focuses on evaluating the effect of Cu/Ni ratio on the physicochemical properties of the bimetallic catalysts and on the catalytic performance of the hydrogenation reaction. NiCux nanoparticles (x = 0.1, 0.2, 0.3) supported on biochar were synthesized by wet impregnation followed by pyrolysis, reduction and passivation, as appropriate. The properties of the catalysts were characterized by TEM, SEM-EDS, TPR-H2, AAS, TGA-MS, FTIR, XRD and N2 adsorption/desorption. The effect of thermal processes on the conversion and selectivity parameters was also evaluated. The reaction was carried out in a batch reactor at 130°C, 20 bar H2, 700 rpm, for 6 hours. The results show that the introduction of copper reduces the size of the nanoparticles and contributes to increase their dispersion on the surface. However, by TEM, agglomeration zones were observed on the support, attributed to the difficulty of the metallic particles to enter the porosities due to their large size. XRD and SEM-EDS confirmed the formation of the Ni-Cu alloy, while TGA-MS analysis indicated that during reduction, the biochar underwent decomposition and methanation, catalyzed by the presence of Ni. The reaction results show that the pyrolysis and reduction sequence is the indicated one to ensure the presence of active sites, while passivation does not contribute to improve the catalytic performance. Nevertheless, the NiCux bimetallic catalysts presented lower conversions compared to the mono metal, independent of the heat treatment applied. Therefore, the biochar-supported bimetallic structure is not suitable for nitrobenzene hydrogenation. It is proposed that the physicochemical properties and structural instability of the support in addition to the metal/biochar interaction inhibit the cooperative effect of the Ni-Cu alloy formed, impairing the conversion of nitrobenzene to aniline.
The catalytic liquid-phase hydrogenation of nitrobenzene is the main method for the synthesis of aniline, a key precursor in the pharmaceutical industry. This reaction occurs through the reduction of the nitro group in the presence of a reducing agent such as H2 and an optimal catalyst for the activation of both reagents. Among the most effective and economical alternatives to noble metals are supported non-noble metal catalysts such as nickel. To promote their catalytic performance, the formation of a bimetallic alloy has been proposed, where the properties and activity of the main metal are enhanced. This study focuses on evaluating the effect of Cu/Ni ratio on the physicochemical properties of the bimetallic catalysts and on the catalytic performance of the hydrogenation reaction. NiCux nanoparticles (x = 0.1, 0.2, 0.3) supported on biochar were synthesized by wet impregnation followed by pyrolysis, reduction and passivation, as appropriate. The properties of the catalysts were characterized by TEM, SEM-EDS, TPR-H2, AAS, TGA-MS, FTIR, XRD and N2 adsorption/desorption. The effect of thermal processes on the conversion and selectivity parameters was also evaluated. The reaction was carried out in a batch reactor at 130°C, 20 bar H2, 700 rpm, for 6 hours. The results show that the introduction of copper reduces the size of the nanoparticles and contributes to increase their dispersion on the surface. However, by TEM, agglomeration zones were observed on the support, attributed to the difficulty of the metallic particles to enter the porosities due to their large size. XRD and SEM-EDS confirmed the formation of the Ni-Cu alloy, while TGA-MS analysis indicated that during reduction, the biochar underwent decomposition and methanation, catalyzed by the presence of Ni. The reaction results show that the pyrolysis and reduction sequence is the indicated one to ensure the presence of active sites, while passivation does not contribute to improve the catalytic performance. Nevertheless, the NiCux bimetallic catalysts presented lower conversions compared to the mono metal, independent of the heat treatment applied. Therefore, the biochar-supported bimetallic structure is not suitable for nitrobenzene hydrogenation. It is proposed that the physicochemical properties and structural instability of the support in addition to the metal/biochar interaction inhibit the cooperative effect of the Ni-Cu alloy formed, impairing the conversion of nitrobenzene to aniline.
Description
Tesis presentada para optar al título de Ingeniera Civil Química
Keywords
Catalizadores, Hidrogenación, Níquel, Cobre