Valorización de furfural empleando catalizadores de metales nobles soportados en TiO2 para la producción de Fuberidazol.
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Date
2026
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Universidad de Concepción
Abstract
La creciente necesidad de desarrollar procesos químicos más sostenibles ha impulsado el aprovechamiento de materias primas renovables, como el furfural (FUR), una de las principales plataformas químicas derivadas de la biomasa lignocelulósica. Entre sus transformaciones más atractivas destaca la síntesis de benzimidazoles 2-sustituidos en particular, el fuberizadol (FUBE), fungicida biomimético de amplio espectro utilizado en tratamientos pre- y post-cosecha. La ruta de síntesis más prometedora combina la aminación reductiva-ciclación de 2-nitroanilina (2NA) y aldehídos seguida de deshidrogenación oxidativa sobre catalizadores de metales soportados, en la que el hidrógeno liberado durante esta última etapa es reutilizado por el sistema catalítico, estableciendo un proceso de pseudo-autotransferencia de hidrógeno (p-ATH) que reduce el consumo de H2 externo. Sin embargo, se desconoce cómo la naturaleza del metal, la carga metálica, el tamaño de partícula y las interacciones fuertes metal-soporte (SMSI) determinan las propiedades estructurales y electrónicas del catalizador, así como su actividad, selectividad y estabilidad. Por lo anterior, en la presente tesis doctoral se desarrollaron y caracterizaron catalizadores de Pd e Ir soportados sobre TiO2-anatasa con cargas entre 0.25 y 2.00% m/m y reducidos a 200 o 500 °C, con el fin de establecer la relación estructura-actividad que permitan racionalizar el diseño de sistemas activos, selectivos y reciclables para la síntesis one-pot de FUBE.
La serie de catalizadores de Pd mostró que el tamaño de las nanopartículas (NPs) controló el comportamiento catalítico: el catalizador 0.50Pd/TiO2 reducido a 200 °C (0.50Pd/TiO2-2) exhibió el mejor desempeño (92% de conversión de 2NA y 45% de selectividad hacia FUBE tras 1440 min), asociado a una distribución heterogénea de NPs con sitios superficiales de distinto ambiente de coordinación. La reducción a 500°C (0.50Pd/TiO2-5) incrementó la selectividad hasta 70%, manteniendo una elevada conversión (96%); análisis de STEM, XPS, HRTEM y DRIFT-CO atribuyeron esta mejora al recubrimiento parcial de las NPs por especies TiOx lo que modificó la disponibilidad de sitios metálicos y ácidos de Lewis, modulando la interfaz Pd-TiO2 en favor de las etapas de condensación y ciclación frente a la hidrogenación. Por su parte, la serie de catalizadores de Ir mantuvo un tamaño de NPs prácticamente constante (1-2 nm) entre 0.25 y 1.00 % m/m, incrementándose solo con la carga más alta (2.81 ± 0.53 nm). El catalizador 0.50Ir/TiO2 reducido a 200 °C (0.50Ir/TiO2-2) presentó el mejor desempeño de la serie (92% de conversión de 2NA y una selectividad de 84% a FUBE), comportamiento gobernado por la reducibilidad de las especies superficiales de Ir y la extensión de la interfaz Ir-TiO2. La inducción del efecto SMSI (0.50Ir/TiO2-5) elevó la selectividad al 96% sin afectar la conversión; esta mejora no se relacionó con cambios en el tamaño de partícula, sino con la modulación de la interfaz Ir-TiO2 — mediante el recubrimiento parcial por especies TiOx — y el efecto de la temperatura de reducción en la reducibilidad superficial y la disponibilidad de sitios metálicos y ácidos de Lewis.
Finalmente, los catalizadores de mejor desempeño (0.50Pd/TiO2-5 y 0.50Ir/TiO2-5) mostraron versatilidad frente a distintas 2-nitroanilinas sustituidas y derivados de FUR, con el sistema de Ir alcanzando mayor actividad, selectividad y menor formación de subproductos. La inducción del efecto SMSI mejoró la estabilidad de ambos catalizadores, aunque se observó una pérdida gradual de actividad debido a la formación de huminas. En conjunto, estos resultados demuestran que la naturaleza del metal, la carga metálica y el efecto SMSI modulan las propiedades estructurales y electrónicas de estos catalizadores, aportan criterios para el diseño racional de catalizadores destinados a procesos one-pot de valorización de biomasa.
The growing need to develop more sustainable chemical processes has driven the use of renewable raw materials, such as furfural (FUR), one of the main chemical platforms derived from lignocellulosic biomass. Among its most attractive transformations is the synthesis of 2-substituted benzimidazoles, particularly fuberizadol (FUBE), a broad-spectrum biomimetic fungicide used in pre- and post-harvest treatments. The most promising synthetic route combines the reductive amination-cyclization of 2-nitroaniline (2NA) and aldehydes followed by oxidative dehydrogenation over supported metal catalysts. In this process, the hydrogen released during the latter step is reused by the catalytic system, establishing a pseudo-hydrogen autotransfer (p-ATH) process that reduces external H2 consumption. However, it remains unclear how metal nature, loading, particle size, and strong metal-support interactions (SMSI) determine the catalyst's structural and electronic properties, as well as its activity, selectivity, and stability. Therefore, this doctoral thesis developed and characterized Pd and Ir catalysts supported on TiO2-anatase, with loadings between 0.25 and 2.00% w/w, reduced at 200 or 500 °C. The aim was to establish a structure-activity relationship that would allow rational design of active, selective, and recyclable systems for the one-pot synthesis of FUBE. The series of Pd catalysts showed that nanoparticle (NP) size controlled catalytic behavior: the 0.50Pd/TiO2 catalyst reduced at 200 °C (0.50Pd/TiO2-2) exhibited the best performance (92% conversion of 2NA and 45% selectivity towards FUBE after 1440 min), associated with a heterogeneous distribution of NPs with surface sites in different coordination environments. Reduction at 500 °C (0.50Pd/TiO2-5) increased selectivity to 70%, while maintaining high conversion (96%). STEM, XPS, HRTEM, and DRIFT-CO analyses attributed this improvement to the partial coating of the NPs by TiOx species, which modified the availability of metal and Lewis acid sites, modulating the Pd-TiO2 interface in favor of condensation and cyclization steps over hydrogenation. Meanwhile, the Ir catalyst series maintained a virtually constant NP size (1–2 nm) between 0.25 and 1.00% w/w, increasing only with the highest loading (2.81 ± 0.53 nm). The 0.50Ir/TiO2 catalyst reduced at 200 °C (0.50Ir/TiO2-2) exhibited the best performance of the series (92% conversion of 2NA and 84% selectivity to FUBE), a behavior governed by the reducibility of the Ir surface species and the extent of the Ir-TiO2 interface. Inducing the SMSI effect (0.50Ir/TiO2-5) increased selectivity to 96% without affecting conversion. This improvement was not related to changes in particle size, but rather to modulation of the Ir-TiO2 interface through partial coating by TiOx species, and to the effect of the reduction of temperature on surface reducibility and the availability of metal and Lewis acid sites. Finally, the best-performing catalysts (0.50Pd/TiO2-5 and 0.50Ir/TiO2-5) showed versatility with different substituted 2-nitroanilines and FUR derivatives, with the Ir system achieving higher activity and selectivity and lower byproduct formation. The SMSI effect improved the stability of both catalysts, although a gradual loss of activity was observed due to humin formation. Taken together, these results show that the metal identity, metal loading, and SMSI effect modulate the structural and electronic properties of these catalysts, providing criteria for the rational design of catalysts for one-pot biomass valorization processes.
The growing need to develop more sustainable chemical processes has driven the use of renewable raw materials, such as furfural (FUR), one of the main chemical platforms derived from lignocellulosic biomass. Among its most attractive transformations is the synthesis of 2-substituted benzimidazoles, particularly fuberizadol (FUBE), a broad-spectrum biomimetic fungicide used in pre- and post-harvest treatments. The most promising synthetic route combines the reductive amination-cyclization of 2-nitroaniline (2NA) and aldehydes followed by oxidative dehydrogenation over supported metal catalysts. In this process, the hydrogen released during the latter step is reused by the catalytic system, establishing a pseudo-hydrogen autotransfer (p-ATH) process that reduces external H2 consumption. However, it remains unclear how metal nature, loading, particle size, and strong metal-support interactions (SMSI) determine the catalyst's structural and electronic properties, as well as its activity, selectivity, and stability. Therefore, this doctoral thesis developed and characterized Pd and Ir catalysts supported on TiO2-anatase, with loadings between 0.25 and 2.00% w/w, reduced at 200 or 500 °C. The aim was to establish a structure-activity relationship that would allow rational design of active, selective, and recyclable systems for the one-pot synthesis of FUBE. The series of Pd catalysts showed that nanoparticle (NP) size controlled catalytic behavior: the 0.50Pd/TiO2 catalyst reduced at 200 °C (0.50Pd/TiO2-2) exhibited the best performance (92% conversion of 2NA and 45% selectivity towards FUBE after 1440 min), associated with a heterogeneous distribution of NPs with surface sites in different coordination environments. Reduction at 500 °C (0.50Pd/TiO2-5) increased selectivity to 70%, while maintaining high conversion (96%). STEM, XPS, HRTEM, and DRIFT-CO analyses attributed this improvement to the partial coating of the NPs by TiOx species, which modified the availability of metal and Lewis acid sites, modulating the Pd-TiO2 interface in favor of condensation and cyclization steps over hydrogenation. Meanwhile, the Ir catalyst series maintained a virtually constant NP size (1–2 nm) between 0.25 and 1.00% w/w, increasing only with the highest loading (2.81 ± 0.53 nm). The 0.50Ir/TiO2 catalyst reduced at 200 °C (0.50Ir/TiO2-2) exhibited the best performance of the series (92% conversion of 2NA and 84% selectivity to FUBE), a behavior governed by the reducibility of the Ir surface species and the extent of the Ir-TiO2 interface. Inducing the SMSI effect (0.50Ir/TiO2-5) increased selectivity to 96% without affecting conversion. This improvement was not related to changes in particle size, but rather to modulation of the Ir-TiO2 interface through partial coating by TiOx species, and to the effect of the reduction of temperature on surface reducibility and the availability of metal and Lewis acid sites. Finally, the best-performing catalysts (0.50Pd/TiO2-5 and 0.50Ir/TiO2-5) showed versatility with different substituted 2-nitroanilines and FUR derivatives, with the Ir system achieving higher activity and selectivity and lower byproduct formation. The SMSI effect improved the stability of both catalysts, although a gradual loss of activity was observed due to humin formation. Taken together, these results show that the metal identity, metal loading, and SMSI effect modulate the structural and electronic properties of these catalysts, providing criteria for the rational design of catalysts for one-pot biomass valorization processes.
Description
Tesis presentada para optar al grado de Doctor/a en Ciencias con mención en Química.
Keywords
Furaldehido, Catalizadores, Fungicidas