Valorization of CO2 into light olefins by thermal-catalytic hydrogenation
Doctoral thesis, 2024
Ending the dependence on fossil resources and reducing greenhouse gas emissions are the main trends in energy technology development. In recent years, with the large-scale application of renewable resources and the popularization of water electrolysis technologies for green hydrogen production, the catalytic valorization of CO2 and green H2 into high-value-added light olefins (ethylene, propene, and butene) is ushering in major opportunities. CO2 will no longer be treated as a waste but will be an important carbon resource for producing chemicals and fuels in the future. In this thesis, two main catalytic technologies for hydrogenation of CO2 to light olefins were studied: (i) Methanol intermediate pathway using the tandem catalysts containing CO2 to methanol (CTM) and methanol to olefins (MTO) catalyst components. (ii) CO intermediate pathway using iron-based Fischer-Tropsch synthesis (FTS) catalysts. These studies are intended to lay a technical and theoretical foundation for the future development of stable industrial catalysts.
One major goal was to develop a tandem catalyst with high stability and minimal CO selectivity. Firstly, two series of single In2O3 and binary In2O3-ZrO2 catalysts were synthesized by combustion, urea hydrolysis, and precipitation methods with different precipitants. The physicochemical properties were characterized and correlated with CTM reaction performance. The results indicated that the synthesis methods significantly influence the catalysts’ specific surface area, crystal structure, and catalytic performance. Moreover, the In2O3-ZrO2 catalysts exhibited superior performance compared to the In2O3 counterparts. Secondly, two types of SSZ-13 zeolites with similar bulk composition, but different framework Al distribution (isolated and paired Al in framework) were synthesized as MTO components in tandem catalysts. Their performance was investigated at a low temperature of CO2 hydrogenation, and the main acid properties (acid density and distribution) influencing selectivity for olefins and coke formation were explored. The results revealed that the Brønsted acid density of zeolites is the primary factor affecting product selectivity and coke formation. Thirdly, over an optimized tandem catalyst with a low acidity SSZ-13 zeolite component and a stable In2O3 component, a transient experiment with varying reaction conditions was carried out to investigate the formation and degradation of trapped coke during CO2 hydrogenation. A dynamic balance mechanism between the formation and degradation of coke was identified, and a pre-coking method was proposed to enhance catalyst selectivity and stability. This mechanism was validated through a 100-hour stability test, confirming that pre-coking improved the performance of SSZ-13 within the In2O3/SSZ-13 tandem catalyst.
To develop a stable iron-based catalyst that can effectively convert CO and CO2 into light olefins, nano-Fe5C2 and nano-Fe3O4 materials, with and without sodium additives, were first synthesized as model catalysts. Their catalytic activities were tested, and the iron phase transitions which closely influence product selectivity and stability were studied under both reaction and regeneration conditions. The results showed that the interface between Na2CO3 and Fe5C2 was the active center for olefins production. However, the Fe5C2 component was prone to oxidation to Fe3O4, especially when mixed with Na2CO3, which reduced selectivity for methane and increased CO selectivity in CO2 hydrogenation. Reducing the gas hourly space velocity (GHSV) lowered CO selectivity and maintained high olefin selectivity, however it also accelerated the oxidation of the Na2CO3-modified nano-Fe5C2 catalyst. Additionally, a series of pure Fe, Fe-Zn, Fe-Mn, and Fe-Zn-Mn spinel-derived catalysts were prepared using a solvothermal method. Their activity and stability were investigated through accelerated deactivation experiments. The results revealed that strong interactions between Fe and Zn or Mn in the lattice changed the reduction, carburization, and oxidation rates of iron species, leading to the formation of dynamic active centers with prolonged catalytic stability during CO2 hydrogenation.
One major goal was to develop a tandem catalyst with high stability and minimal CO selectivity. Firstly, two series of single In2O3 and binary In2O3-ZrO2 catalysts were synthesized by combustion, urea hydrolysis, and precipitation methods with different precipitants. The physicochemical properties were characterized and correlated with CTM reaction performance. The results indicated that the synthesis methods significantly influence the catalysts’ specific surface area, crystal structure, and catalytic performance. Moreover, the In2O3-ZrO2 catalysts exhibited superior performance compared to the In2O3 counterparts. Secondly, two types of SSZ-13 zeolites with similar bulk composition, but different framework Al distribution (isolated and paired Al in framework) were synthesized as MTO components in tandem catalysts. Their performance was investigated at a low temperature of CO2 hydrogenation, and the main acid properties (acid density and distribution) influencing selectivity for olefins and coke formation were explored. The results revealed that the Brønsted acid density of zeolites is the primary factor affecting product selectivity and coke formation. Thirdly, over an optimized tandem catalyst with a low acidity SSZ-13 zeolite component and a stable In2O3 component, a transient experiment with varying reaction conditions was carried out to investigate the formation and degradation of trapped coke during CO2 hydrogenation. A dynamic balance mechanism between the formation and degradation of coke was identified, and a pre-coking method was proposed to enhance catalyst selectivity and stability. This mechanism was validated through a 100-hour stability test, confirming that pre-coking improved the performance of SSZ-13 within the In2O3/SSZ-13 tandem catalyst.
To develop a stable iron-based catalyst that can effectively convert CO and CO2 into light olefins, nano-Fe5C2 and nano-Fe3O4 materials, with and without sodium additives, were first synthesized as model catalysts. Their catalytic activities were tested, and the iron phase transitions which closely influence product selectivity and stability were studied under both reaction and regeneration conditions. The results showed that the interface between Na2CO3 and Fe5C2 was the active center for olefins production. However, the Fe5C2 component was prone to oxidation to Fe3O4, especially when mixed with Na2CO3, which reduced selectivity for methane and increased CO selectivity in CO2 hydrogenation. Reducing the gas hourly space velocity (GHSV) lowered CO selectivity and maintained high olefin selectivity, however it also accelerated the oxidation of the Na2CO3-modified nano-Fe5C2 catalyst. Additionally, a series of pure Fe, Fe-Zn, Fe-Mn, and Fe-Zn-Mn spinel-derived catalysts were prepared using a solvothermal method. Their activity and stability were investigated through accelerated deactivation experiments. The results revealed that strong interactions between Fe and Zn or Mn in the lattice changed the reduction, carburization, and oxidation rates of iron species, leading to the formation of dynamic active centers with prolonged catalytic stability during CO2 hydrogenation.
Indium oxides catalyst
methanol synthesis
MTO reaction
Iron catalyst
SSZ-13
CO2 hydrogenation
spinel
tandem catalysts
stability.
Fischer-Tropsch synthesis
light olefins
pre-coking
Vasa C, Vera Sandbergs Allé 8, Gothenburg, Sweden
Opponent: Prof. Edd Anders Blekkan, Norwegian University of Science and Technology, Gløshaugen, Norway.
Author
Wei Di
Chalmers, Chemistry and Chemical Engineering, Chemical Technology
Effect of the Preparation Methods on the Physicochemical Properties of Indium-Based Catalysts and Their Catalytic Performance for CO<inf>2</inf> Hydrogenation to Methanol
Energy & Fuels,;Vol. 38(2024)p. 5407-5420
Journal article
CO2 hydrogenation to light olefins using In2O3 and SSZ-13 catalyst-Understanding the role of zeolite acidity in olefin production
Journal of CO2 Utilization,;Vol. 72(2023)
Journal article
Modulating the Formation of Coke to Improve the Production of Light Olefins from CO2 Hydrogenation over In2O3 and SSZ-13 Catalysts
Energy & Fuels,;Vol. 37(2023)p. 17382-17398
Journal article
Investigation of the dynamic active center for CO2 hydrogenation to light olefins over Na-modified nanosized iron catalysts
Na decorated Mn-Zn ferrite spinel-derived catalysts for CO2 hydrogenation to light olefins.
The surge in global energy demand, coupled with an over-reliance on fossil fuels, has led to a sharp increase in CO2 emissions over the past hundred years. In response to these crises, the European Union has proposed an ambitious goal and strategies to achieve net zero greenhouse gas emissions by 2050. Among many approaches, catalytic hydrogenation of CO2 into high-value-added light olefins is recognized as one of the vital strategies for reducing CO2 emissions, promoting sustainable carbon resource utilization, and advancing green chemistry development.
However, activating CO2 molecule presents greater challenges, and its hydrogenation process is hindered by the adverse effects of the high water partial pressure in its products. Enhancing catalyst stability while maintaining high selectivity for light olefins remains one of the major challenges limiting its industrial application.
In this thesis, two catalyst systems (tandem catalysts and iron-based catalysts) were systematically studied. Beginning with the synthesis of specialized catalytic materials, this research investigated the factors influencing the catalytic active centers and key process parameters impacting catalyst lifespan, using a combination of physicochemical characterization and catalytic reactivity experiments. This approach uncovered distinct types of dynamic active centers and proposed strategies to enhance catalyst stability through optimized process design and material innovation tailored for these two different catalyst types.
However, activating CO2 molecule presents greater challenges, and its hydrogenation process is hindered by the adverse effects of the high water partial pressure in its products. Enhancing catalyst stability while maintaining high selectivity for light olefins remains one of the major challenges limiting its industrial application.
In this thesis, two catalyst systems (tandem catalysts and iron-based catalysts) were systematically studied. Beginning with the synthesis of specialized catalytic materials, this research investigated the factors influencing the catalytic active centers and key process parameters impacting catalyst lifespan, using a combination of physicochemical characterization and catalytic reactivity experiments. This approach uncovered distinct types of dynamic active centers and proposed strategies to enhance catalyst stability through optimized process design and material innovation tailored for these two different catalyst types.
Driving Forces
Sustainable development
Areas of Advance
Energy
Subject Categories
Chemical Process Engineering
Chemical Engineering
Materials Chemistry
Chemical Sciences
Roots
Basic sciences
Infrastructure
Chalmers Materials Analysis Laboratory
ISBN
978-91-8103-130-0
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5588
Publisher
Chalmers
Vasa C, Vera Sandbergs Allé 8, Gothenburg, Sweden
Opponent: Prof. Edd Anders Blekkan, Norwegian University of Science and Technology, Gløshaugen, Norway.