Síntesis, caracterización y evaluación cinética de un catalizador bifuncional InZr-Zeolita para la hidrogenación de CO2 a olefinas ligeras.
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Date
2025
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Universidad de Concepción
Abstract
La hidrogenación de CO2 hacia olefinas ligeras representa una alternativa sustentable frente a la producción convencional basada en craqueo de hidrocarburos. Para ello, se requiere un diseño preciso e inteligente de acoplamiento entre fases en catalizadores bifuncionales. En este contexto, los sistemas In2O3–ZrO2/SAPO-34 han demostrado ser prometedores debido a la sinergia entre las fases activas para transformar el CO2 en metanol (In2O3–ZrO2) y el metanol en olefinas (SAPO-34).
El presente trabajo muestra el efecto estructural y cinético de la síntesis de catalizadores bifuncionales compuestos por óxidos de indio (4,3 %p/p de In2O3), y óxido de circonio (ZrO2) soportados sobre SAPO-34 sobre la conversión de la reacción de transformación de CO2 en olefinas ligeras (etileno y propileno). Se sintetizaron dos catalizadores mediante impregnación húmeda incipiente (IWI) de SAPO-34 con solo In2O3 y otro con impregnación secuencial de ZrO2 e In2O3, comparándolos con un lecho catalítico formado por mezclado físico de la fase ácida (SAPO-34) y la redox (In2O3-ZrO2). Todos los materiales se caracterizaron por XRD, TGA, NH3-TPD y H2-TPR. Las pruebas de actividad fueron realizadas en un reactor de lecho fijo a presión absoluta de 8 bar, razón de flujo H2/CO2 igual a 4 y temperaturas entre 280°C y 350°C. Además, se evaluó el efecto del tiempo de residencia variando el flujo volumétrico entre 40 – 65 ml/min a una condición fija de 280°C, una presiones de H2 de 640 kPa y variando la presión de CO2 de 80 a160 kPa.
Los análisis XRD confirmaron una alta dispersión de los óxidos, sin formación de fases cristalinas detectables. Los resultados de TPD-NH3 revelaron una disminución significativa de la acidez Brønsted en los materiales impregnados (con respecto a SAPO-34), especialmente en In/SP-IWI, atribuida al intercambio iónico con In3+ con el sitio Brønsted. Además, los perfiles TPR mostraron especies redox similares en todos los catalizadores bifuncionales, con reducción cercana a los 400 °C, con una distribución de tamaños de cristal estrecha. Los resultados cinéticos mostraron que los catalizadores impregnados favorecen la formación de metano sobre metanol, limitando así la generación de olefinas ligeras. Este comportamiento se atribuye principalmente a una pérdida significativa de acidez Brønsted por intercambio iónico (In3+/H+). En contraste, el lecho catalítico de mezclado físico de la fase ácida con la redox presentó una mayor producción de olefinas, atribuida a una mayor producción, y por ende disponibilidad, del intermedio metanol y mayor densidad sitios ácidos. Se concluye que el método de síntesis y la proximidad espacial entre fases activas impactan directamente en la ruta de reacción, selectividad y rendimiento.
The hydrogenation of CO2 to light olefins represents a sustainable alternative to conventional hydrocarbon-cracking-based production. Achieving this requires a precise and intelligent design of phase coupling in bifunctional catalysts. In this context, In2O3–ZrO2/SAPO-34 systems have proven to be promising due to the synergy between the active phases for converting CO2 to methanol (In2O3–ZrO2) and methanol to olefins (SAPO-34). This work presents the structural and kinetic effects of the synthesis of bifunctional catalysts composed of indium oxide (4,3 wt% In2O3) and zirconium oxide (ZrO2) supported on SAPO-34 on the conversion of CO2 to light olefins (ethylene and propylene). Two catalysts were synthesized via incipient wetness impregnation (IWI) of SAPO-34: one with only In₂O₃ and another with sequential impregnation of ZrO2 and In2O3 and were compared with a catalytic bed formed by the physical mixing of the acidic phase (SAPO-34) and the redox phase (In2O3–ZrO2). All materials were characterized by XRD, TGA, NH3-TPD, and H2-TPR. Activity tests were carried out in a fixed-bed reactor at 8 bar absolute pressure, with an H2/CO2 feed ratio of 4 and temperatures between 280 °C and 350 °C. In addition, the effect of residence time was evaluated by varying the volumetric flow between 40–65 ml/min under fixed conditions of 280 °C, H2 partial pressure of 640 kPa, and CO₂ partial pressure varying from 80 to 160 kPa. XRD analyses confirmed a high dispersion of oxides, with no detectable crystalline phases. NH₃-TPD results revealed a significant decrease in Brønsted acidity in the impregnated materials (compared to SAPO-34), especially in In/SP-IWI, attributed to ion exchange between In3+ and Brønsted sites. Moreover, TPR profiles showed similar redox species in all bifunctional catalysts, with reduction occurring near 400 °C and a narrow crystal size distribution. Kinetic results indicated that the impregnated catalysts favor methane formation over methanol, thus limiting the generation of light olefins. This behavior is mainly attributed to a significant loss of Brønsted acidity due to ion exchange (In3+/H+). In contrast, the catalytic bed formed by physical mixing of the acidic and redox phases showed higher olefin production, attributed to greater methanol generation (and thus availability) and higher acid site density. It is concluded that the synthesis method and spatial proximity between active phases directly impact the reaction pathway, selectivity, and yield.
The hydrogenation of CO2 to light olefins represents a sustainable alternative to conventional hydrocarbon-cracking-based production. Achieving this requires a precise and intelligent design of phase coupling in bifunctional catalysts. In this context, In2O3–ZrO2/SAPO-34 systems have proven to be promising due to the synergy between the active phases for converting CO2 to methanol (In2O3–ZrO2) and methanol to olefins (SAPO-34). This work presents the structural and kinetic effects of the synthesis of bifunctional catalysts composed of indium oxide (4,3 wt% In2O3) and zirconium oxide (ZrO2) supported on SAPO-34 on the conversion of CO2 to light olefins (ethylene and propylene). Two catalysts were synthesized via incipient wetness impregnation (IWI) of SAPO-34: one with only In₂O₃ and another with sequential impregnation of ZrO2 and In2O3 and were compared with a catalytic bed formed by the physical mixing of the acidic phase (SAPO-34) and the redox phase (In2O3–ZrO2). All materials were characterized by XRD, TGA, NH3-TPD, and H2-TPR. Activity tests were carried out in a fixed-bed reactor at 8 bar absolute pressure, with an H2/CO2 feed ratio of 4 and temperatures between 280 °C and 350 °C. In addition, the effect of residence time was evaluated by varying the volumetric flow between 40–65 ml/min under fixed conditions of 280 °C, H2 partial pressure of 640 kPa, and CO₂ partial pressure varying from 80 to 160 kPa. XRD analyses confirmed a high dispersion of oxides, with no detectable crystalline phases. NH₃-TPD results revealed a significant decrease in Brønsted acidity in the impregnated materials (compared to SAPO-34), especially in In/SP-IWI, attributed to ion exchange between In3+ and Brønsted sites. Moreover, TPR profiles showed similar redox species in all bifunctional catalysts, with reduction occurring near 400 °C and a narrow crystal size distribution. Kinetic results indicated that the impregnated catalysts favor methane formation over methanol, thus limiting the generation of light olefins. This behavior is mainly attributed to a significant loss of Brønsted acidity due to ion exchange (In3+/H+). In contrast, the catalytic bed formed by physical mixing of the acidic and redox phases showed higher olefin production, attributed to greater methanol generation (and thus availability) and higher acid site density. It is concluded that the synthesis method and spatial proximity between active phases directly impact the reaction pathway, selectivity, and yield.
Description
Tesis presentada para optar al título de Ingeniero/a Civil Químico/a.
Keywords
Zeolitas, Catalizadores, Hidrogenación, Olefinas