Modulación de la selectividad de la hidrogenación de CO2 mediante adición de Sn a catalizadores de Cu.
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Date
2025
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Universidad de Concepción
Abstract
Este trabajo estudió la modulación en la selectividad en la hidrogenación de CO2 añadiendo Sn: (i) en catalizadores Cu/ZrO2, alterando sólo la razón molar ϕ = Sn/(Cu+Sn) desde cero hasta 0,5 vía impregnación húmeda modificada; (ii) sobre un soporte inerte Cu/SiO2; (iii) en catalizadores inversos ZrO2/Cu vía coprecipitación y (iv) como soporte en un catalizador Cu-ZrO2/SnO2. Además, se discutió la sinergia bimetálica Cu-Sn y se comparó con trabajos previos.
La caracterización de los catalizadores tras la adición de Sn se realizó por análisis de difracción de rayos X, reducción a temperatura programada con H2 y titulación con N2O, microscopía por transmisión de electrones y espectroscopía de absorción atómica: catalizadores Cu/ZrO2 presentan partículas de Cu bien dispersas y se forman aleaciones Cu-Sn que estabilizan la presencia metálica de Sn ex situ. El H2 consumido por los catalizadores soportados en óxidos comerciales es congruente con la reducción completa de Cu y la adición de Sn hasta ϕ = 0,2. Sobre ZrO2/Cu, la adición de Sn sinteriza visiblemente el catalizador in situ. El soporte sintetizado, SnO2, es amorfo y migra para formar aleaciones con Cu en la superficie.
La cinética se estudió a 8 bar desde 220ºC a 280ºC en un reactor de lecho empacado diferencial. El catalizador Cu-Sn/ZrO2–0,05 exhibe el mejor desempeño en selectividad hacia metanol. Para relaciones molares ϕ ≤ 0,05, se logra inhibir los sitios activos para la formación de CO, sin comprometer la velocidad de formación de metanol. Al cambiar el soporte por uno inerte, la adición de Sn disminuye casi en dos órdenes de magnitud la velocidad de formación de CO y uno para metanol, promoviendo significativamente la selectividad desde 1% en Cu/SiO2 hasta 15% en Cu-Sn/SiO2–0,2. En la estructura inversa, destaca el comportamiento similar en actividad y selectividad de ZrO2/Cu con el catalizador comercial Cu/ZnO/Al2O3. Finalmente, se proponen estrategias para continuar el estudio de las líneas investigativas que este trabajo inaugura.
This work studied the modulation in selectivity in CO2 hydrogenation by adding Sn: (i) on Cu/ZrO2 catalysts, varying only the molar ratio ϕ = Sn/(Cu+Sn) from zero to 0.5 via modified wet impregnation; (ii) on an inert Cu/SiO2 support; (iii) on ZrO2/Cu inverse catalysts via coprecipitation and (iv) as a support in a Cu-ZrO2/SnO2 catalyst. In addition, the Cu-Sn bimetallic synergy was discussed and compared with previous work. The characterization of the catalysts after Sn addition was performed by X-ray diffraction analysis, programmed temperature reduction with H2, transmission electron microscopy and atomic absorption spectroscopy: CuSn alloys are formed with increasing tin aggregation, and these manage to stabilize the presence of Sn0 under ambient conditions. Catalysts supported over commercial oxides (m-ZrO2 and SiO2) obtain consumption ratios H2/Cu > 1, demonstrating that all Cu is reduced to its metallic state and Sn is reduced proportionally to its theorical addition. In inverse catalysts (ZrO2/Cu), the addition of Sn visibly sinters Cu and decreases the adsorption capacity. The synthesized support, SnO2, is amorphous and migrates to the surface to form alloys with Cu. The kinetics were studied from 220ºC to 280ºC at 8 bar in a differential packed bed reactor. The Cu-Sn/ZrO2 – 0.05 catalyst exhibits the best performance in selectivity towards methanol. For molar ratios ϕ ≤ 0.05, the active sites for CO formation are inhibited and their nature is changed, without modifying the methanol formation rate. By changing the support to an inert one, the addition of Sn decreases the formation rate of CO by almost twofold and that of methanol by onefold, significantly promoting the selectivity from 1% in Cu/SiO2 to 15% in Cu-Sn/SiO2 – 0.2. For the inverse structure, a similar behaviour in activity and selectivity of ZrO2/Cu with the commercial catalyst Cu/ZnO/Al2O3 stands out. Finally, strategies are proposed to continue the study of the research lines inaugurated by this work.
This work studied the modulation in selectivity in CO2 hydrogenation by adding Sn: (i) on Cu/ZrO2 catalysts, varying only the molar ratio ϕ = Sn/(Cu+Sn) from zero to 0.5 via modified wet impregnation; (ii) on an inert Cu/SiO2 support; (iii) on ZrO2/Cu inverse catalysts via coprecipitation and (iv) as a support in a Cu-ZrO2/SnO2 catalyst. In addition, the Cu-Sn bimetallic synergy was discussed and compared with previous work. The characterization of the catalysts after Sn addition was performed by X-ray diffraction analysis, programmed temperature reduction with H2, transmission electron microscopy and atomic absorption spectroscopy: CuSn alloys are formed with increasing tin aggregation, and these manage to stabilize the presence of Sn0 under ambient conditions. Catalysts supported over commercial oxides (m-ZrO2 and SiO2) obtain consumption ratios H2/Cu > 1, demonstrating that all Cu is reduced to its metallic state and Sn is reduced proportionally to its theorical addition. In inverse catalysts (ZrO2/Cu), the addition of Sn visibly sinters Cu and decreases the adsorption capacity. The synthesized support, SnO2, is amorphous and migrates to the surface to form alloys with Cu. The kinetics were studied from 220ºC to 280ºC at 8 bar in a differential packed bed reactor. The Cu-Sn/ZrO2 – 0.05 catalyst exhibits the best performance in selectivity towards methanol. For molar ratios ϕ ≤ 0.05, the active sites for CO formation are inhibited and their nature is changed, without modifying the methanol formation rate. By changing the support to an inert one, the addition of Sn decreases the formation rate of CO by almost twofold and that of methanol by onefold, significantly promoting the selectivity from 1% in Cu/SiO2 to 15% in Cu-Sn/SiO2 – 0.2. For the inverse structure, a similar behaviour in activity and selectivity of ZrO2/Cu with the commercial catalyst Cu/ZnO/Al2O3 stands out. Finally, strategies are proposed to continue the study of the research lines inaugurated by this work.
Description
Tesis presentada para optar al título de Ingeniero/a Civil Químico/a.
Keywords
Hidrogenación, Catalizadores de cobre, Procesos químicos