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State-of-Art for the CO2 Utilization
CO2 emissions and impacts
Since the industrial revolution time, the consumption of energy especially fossil fuels (coal, oil, and natural gas) had been increasing significantly. Although new energy resources e.g. nuclear energy, solar, and hydropower, etc. have been developed to reduce the dependence on fossil energy, Most of the energy consumption is still based on fossil fuels. As shown in Fig.2.1, the primary energy supply from 1971 to 2018 nearly kept stable with the fossil fuels (coal, oil, and natural gas) accounting for the majority part (International Energy Agency, IEA). Meanwhile, the combustion of fossil fuels and other industrial activities resulted in the fast increase of CO2 concentration in the atmosphere. According to the world meteorological organization (WMO) greenhouse gas bulletin report in 2019, the atmospheric CO2 concentration has been increasing annually by 2-3 ppm over the last decade . In Fig.2.2, it can be seen that the annual worldwide CO2 emission has been increasing sharply since the last century and the peak of CO2 emission has not been reached until 2019. The quick increase of atmospheric CO2 concentration has caused many severe environmental problems e.g. global warming, climate change, sea level rising, and ocean acidification . In Fig.2.3, it can be seen that the average global temperature has been increasing gradually since the 19th century. The international panel on climate change (IPCC) commission reported that human-induced GHGs emissions had caused the average temperature to increase approximately 1 °C above pre-industrial levels in 2017 and the temperature is increasing at 0.2°C per decade. To mitigate global warming, human society has been taking action to reduce CO2 emissions. In 2015, the Paris Agreement aimed at reducing the CO2 emissions had been adopted by 196 parties in which the goal of the agreement is to limit global warming to 1.5 degrees Celsius compared to pre-industrial levels . In order to reach this long-term target, the international community needs to reach global peaking of GHGs emissions to achieve a climate-neutral world by mid-century. To achieve sustainable development for the human community, many countries have implemented emission reduction policies. For example, China has promised to achieve a carbon-neutral goal in 2060.
Regarding the CO2 emissions reduction, besides limiting the consumption of fossil fuels, the CCS and CCU technologies also help to mitigate the emission. The CCS technology can use the CO2 capture technology to concentrate the CO2 and store the resource in geologic ways. The CCU route can use renewable energy to convert CO2 to valuable resources.
The routes for CO2 storage and utilization
The CO2 capture and storage (CCS).
CO2 sources can be divided into CO2 point sources and atmospheric CO2 sources . CO2 point sources mainly come from the fossil-fueling power plant, petroleum refining, ethylene production, cement production, iron and steel production, ethylene oxide production, hydrogen production, ammonia processing, natural gas processing, and ethanol production chemical plants, paper mills, and fermentation, etc. [20,21]. The CO2 capture routes consist of capturing CO2 from the atmosphere i.e. direct air capture (DAC) and CO2 point sources like the industry sector [21–25]. Fig.2.4 shows a future scenario regarding the capture of CO2 sources in which the capture from fossil fuels accounts for the overwhelming majority. The CO2 emissions from the combustion of coal, oil, and gas accounted for nearly half of the fossil fuel CO2 emissions (30 gigatons annually ) or a quarter of the GHGs emissions [22,23]. CO2 emission from the combustion of fossil fuels including mobile and stationary emissions accounts for 93.74% of the total industrial emissions .
For the capture from air, the atmospheric CO2 can be immobilized by biomass e.g. vegetation, plankton, and algae, etc., or chemical absorbents [22,26]. The direct capture of CO2 (DAC) by technological systems has been developed and applied in the production of CO2-free air, which is widely used in the industrial sector e.g. dry ice production and air separation plants . In these routes, the sorbents like sodium hydroxide (NaOH), potassium hydroxide (KOH), sodium carbonate (Na2CO3), amines are needed to sorb the CO2 and the captured CO2 is concentrated for storage (geologic or undersea storage ) or recycling. For the strong chemical bases such as NaOH and KOH, their regeneration needs high temperature, which costs abundant energy .
The regeneration of amines needs lower temperatures, making them appropriate absorbents. Besides these materials, the novel metal-organic-framework (MOF) materials hybrid ultra-microporous materials (HUMs) were also been used to capture CO2 [28,29]. Such new materials can serve as physisorbed in DAC, which needs low temperature in the regeneration process . Generally, the purer the CO2 emission streams are the lower cost the separation systems are. Thus, capturing CO2 from stationary sites that have purer CO2 could significantly decrease the cost of the CCS system and improving the economic viability for CCS and climate change mitigation.
A typical CCS system from the power plant diagram is displayed in Fig.2.5. It shows the different components of a CCS system and their consequential effects on electricity production. The CO2 was captured from the fossil fuel combustion in the power plant followed by compressing and transporting to storage sites e.g., underground or in salts [30,31]. The captured CO2 can also be directly used in technological applications like dry ice, soft drinks, and supercritical fluid, etc. [1,32,33].
The CO2 capture and utilization (CCU) and why is CO2 utilization important?
Besides the CCS technology, the CO2 capture and utilization (CCU) technologies also play very important roles in CO2 emissions control. The CCS technology normally needs heavy investment especially for the CCS from the air. For example, it will lead to a sharp increase in electricity cost (5-57%) from power plants using CCS . In such cases, the CCU technologies have attracted intensive attention in academic and industrial areas based on their benefits. The CCU technologies can not only help to reduce CO2 emissions but also produce valuable products.
The CCU route is a technology that uses the captured CO2 to produce useful fuels, chemicals, and materials . The CO2 chemical utilization technologies can directly convert the CO2 to fuels, chemicals, and materials [11,33]. The chemicals like urea, salicylic acid, and inorganic carbonates can be obtained by thermal processes. The chemicals/materials that needed catalytic processes concern the production of formic acid, other carboxylates, organic carbonates, carbamates, acrylates from ethene and CO2, and products from olefins, dienes, and alkynes reacting with CO2. The fuel production concentrates on syngas, methanol, higher alcohols, methane, and long-carbon chain hydrocarbon compounds.
In addition to thermal catalysis, electro-catalysis, photo-catalysis, plasma-assisted catalysis, and biochemical routes concerning CO2 conversion have been also developed [4,35–37]. For instance, the production of biofuel via photocatalysis from microalgae using captured CO2 seems to be an alternative route . Among these routes, the CO2 chemical utilization technologies have received the most intensive research interests due to mature technologies and high efficiency . Meanwhile, the other novel approaches are still under research.
Table 2.1 lists various routes towards CO2 chemical utilization. Six criteria such as Potential development and Economic perspectives, which influence the industrial application of CO2 utilization technologies, were taken into account. Their degree of development was evaluated by the number from 1 to 4 and colors. The study was from the French Environment and Energy Management Agency (ADEME) . The criteria used to investigate different CO2 utilization routes were as follow [2,39]:
• Potential development: it indicates the time for the practical industrial facility, which is up to the lab research and development results.
• Economic perspective: it shows the future of obtaining an economic value and reflects the difficulty to achieve economic value.
• External use of energy: it indicates the cost of energy consumption per cost of the product. The energy cost can significantly affect the potential commercialization of the technology, which mainly refers to endothermic processes such as dry methane reforming.
• Potential volume of use of CO2: it indicates the maximum annual amount of CO2 that can be transferred by the year 2050.
• Time of sequestration: it refers to the time of CO2 fixation before it is emitted to the atmosphere.
• Other environmental impacts: they indicate the application of toxic chemicals in the process and hazardous catalysts etc.
Table of contents :
1. General Introduction
2. State-of-Art for the CO2 Utilization
2.1 CO2 emissions and impacts
2.2 The routes for CO2 storage and utilization
2.2.1 The CO2 capture and storage (CCS).
2.2.2 The CO2 capture and utilization (CCU) and why is CO2 utilization important?
2.3 Dry reforming of methane by CO2
2.4 CO2 hydrogenation to methanol
2.4.2 Power-to-methanol systems
2.5 CO2 methanation
2.5.2 Thermodynamic aspects of CO2 methanation
22.214.171.124. The effect of temperature in CO2 methanation simulation
126.96.36.199. The effect of the pressure in CO2 methanation
188.8.131.52. The effect of H2/CO2 ratio in CO2 methanation simulation
2.5.3 Mechanisms of CO2 methanation
184.108.40.206 The CO as intermediate of CO2 hydrogenation mechanism
220.127.116.11 The formate intermediate mechanism
18.104.22.168 On the important presence of side reactions in CO2 methanation reaction
2.5.4 The catalysts for CO2 methanation
22.214.171.124 Noble metal-based catalysts
126.96.36.199 Ni catalysts and other non-noble metal-based catalysts
188.8.131.52.1. Ni-based catalysts
184.108.40.206.2. Other non-noble metal-based catalysts for CO2 methanation
2.5.6 Power-to-gas system (PtG)
220.127.116.11. The PtG projects in European Union
18.104.22.168. Non- European Union: The example of China
3. Experimental part
3.1 Catalyst preparation
3.1.1 Low-cost diatomite supported catalysts
3.1.2 Mixed oxides derived from layered-double hydrotalcite (LDH) materials
3.1.3 Y-promoted novel ceria supported Ni catalysts
3.1.4 Ordered mesoporous SBA-15 and SBA-16 materials supported catalysts
22.214.171.124. Synthesis of NiY/SBA-15 and NiCexY/SBA-15 catalysts
126.96.36.199. Synthesis of SBA-16 supports
188.8.131.52. Ni/xCe/SBA-16 catalysts preparation
184.108.40.206. Synthesis of Ni/xCeY/SBA-16 catalysts
3.2 Catalytic CO2 methanation
3.2.1 Activity test
3.3 Characterization of the supports and catalysts
3.3.1 Temperature-programmed reduction in hydrogen (H2-TPR)
3.3.2 Temperature-programmed desorption in CO2 (CO2-TPD)
3.3.3 Physical adsorption of nitrogen (N2)
3.3.4 Chemisorption of hydrogen (H2 chemisorption)
3.3.5 X-ray diffraction (Small-angle and Wide-angle)
3.3.6 Elemental composition analysis
3.3.7 Transmission electron microscopy and Energy Dispersive X-ray spectroscopy
3.3.8 X-ray photoelectron spectroscopy
3.3.9 Thermogravimetric analyses-mass spectrometer (TGA-MS)
3.3.10 Temperature-programmed oxidation (TPO)
4. Low-cost materials for CO2 methanation
4.1 Ni-Mg catalysts supported on diatomite
4.1.2. Catalyst preparation and Physicochemical techniques
4.1.3 Texture properties and structural parameters of catalysts
4.1.4. Reducibility, basicity distribution of catalysts
4.1.5. Catalytic performance of catalysts for CO2 methanation
4.1.6 Conclusions of diatomite supported Ni-Mg catalysts
4.2 Nickel-based mixed oxides derived from layered-double hydrotalcite (LDH)
4.2.2 Catalyst preparation
4.2.3 Structural parameters, elemental composition, and textural properties of nano-mixed oxides derived from hydrotalcite
4.2.4 Reducibility of catalysts followed by H2-TPR
4.2.5 Basicity of the catalysts derived from CO2-TPD
4.2.6 Catalytic performance tests for CO2 methanation
4.2.7 On the evolution of spent samples
220.127.116.11. Structural Evolution
18.104.22.168. Surface evolution
4.2.8 Conclusions of mixed oxides from LDHs
4.3. Conclusions and perspectives
5. Ni/CeO2 nanoparticles promoted by yttrium doping as catalysts for CO2 methanation
5.2 Catalyst preparation and physicochemical techniques
5.3 Elemental content, textural properties, structural parameters, and surface compositions of the catalysts
5.4 On the reducibility of calcined catalysts
5.5 Morphologies of the catalysts derived from TEM and HRTEM characterization
5.6 Evaluation of oxygen vacancies content and oxygen mobility by TGA analysis
5.7 Basicity distribution of the reduced catalysts derived from CO2-TPD analyses
5.8 Catalytic performance of Ni based catalysts in CO2 methanation
5.9 Relationships between physicochemical properties and catalytic performances
5.10 Steady-state test of Ni/CeO2 based catalysts in CO2 methanation
5.11 Characterization of Ni/CeO2 based catalysts after steady-state test
5.11.1 XRD patterns of the catalysts after steady-state test
5.11.2 XPS analysis of the catalysts after steady-state test
5.12. Conclusions and perspectives
6. Ordered mesoporous silica supported Ni catalysts for CO2 methanation
6.2. SBA-15 supported Ni catalysts doped by Y and Ce
6.2.2 Catalysts preparation and characterization
6.2.3 Textural properties, structural parameters, metal distribution, and chemical surface composition of the studied catalysts
6.2.4 Reducibility of the studied catalysts
6.2.5 Basicity of the studied catalysts
6.2.6 Catalytic performance in CO2 methanation
6.2.7 Stability tests of NiCe/SBA-15 and NiCeY/SBA-15 catalysts at 350 °C
6.2.8 Characterization of catalysts after CO2 methanation reaction
22.214.171.124 XRD patterns of the catalysts after test
126.96.36.199 TGA-MS tests of catalysts after test
6.2.9 Conclusions of Ce and Y promoted Ni/SBA-15 catalysts
6.3 SBA-16 supported Ni catalysts for CO2 methanation: on the effects of Ce or Y promoter
6.3.1 Ce promoted Ni/SBA-16 catalysts for CO2 methanation
188.8.131.52 Materials preparation and characterization
184.108.40.206 Catalytic activity test and stability test
220.127.116.11 Textural properties, structural properties, morphology, and surface states of elements
18.104.22.168 Reducibility of the catalysts originated from H2-TPR
22.214.171.124 Basicity of the catalysts originated from CO2-TPD
126.96.36.199 Catalytic tests of the catalysts in CO2 methanation reaction
188.8.131.52 Stability tests of the catalysts in CO2 methanation reaction
184.108.40.206 XRD patterns of the catalysts after methanation test
220.127.116.11 The selection of pre-treatment temperature and Ce loading based on activity test
18.104.22.168. Comparison of the Ni/Ce/SBA-16 and Ni/CeY/SBA-16 catalysts in CO2 methanation.
6.4 SBA-15 versus SBA-16: a comparison of the catalytic properties
6.4.1 Comparation of SBA-15 and SBA-16 supported catalysts in CO2 hydrogenation
6.4.2 On the basicity properties: SBA-15 versus SBA-16 supported catalysts
6.4.3 Ni particle size comparison between SBA-15 and SBA-16 supported catalysts
6.4.4 Surface atom ratio comparison from XPS between SBA-15 and SBA-16 supported catalysts
7. Conclusion and perspectives of this work
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