Catalytic hydrogenation of CO2 into light olefins has gained increasing attention, nevertheless the design of an efficient catalyst with high selectivity towards light olefins is still challenging. Herein, aiming at improving the selectivity of targeted light olefins, we successfully synthesized a series of Na/MFe2O4 (M = Co, Zn and Cu) spinel catalysts via hydrothermal synthesis, and tried to establish their activity-structure relationship. Among the Na/ MFe2O4 spinel catalysts, the Na/CoFe2O4 catalyst shows superior catalytic performance, thanks to the wellcrystallized CoFe2O4 nanoparticle which has the good dispersibility, reducibility and carburizing ability. Moreover, compared with the traditional Na/Fe-Co catalyst obtained via co-precipitation, the formation of CoFe2O4 with uniform crystal phase and smaller crystal size for Na/CoFe2O4 spinel catalyst is more conducive to the formation of active and stable chi-(CoxFe1_ x)5C2 alloy carbide, thereby resulting in excellent catalytic activity and stability. On this basis, to further improve the C2-4= selectivity, we coupled the Na/CoFe2O4 component with acidic zeolites (e.g., SAPO-34, MOR and H beta), and the Na/CoFe2O4@SAPO-34 catalyst is found to possess a superior C2-4 = selectivity of 42 % with a CO2 conversion of 39 %. This work can provide a useful understanding of designing efficient spinel-structured bimetal catalysts for selective conversion of CO2 into value-added light olefins.

In the context of global carbon neutrality and stringent environmental constraints, gas-to-methanol (GTM) process has emerged as a pivotal pathway for sustainable methanol production. The CO2/(CO + CO2) ratios in the intermediate syngas have crucial influences on the reaction and process performances. However, the lack of consensus on the optimal CO2/(CO + CO2) ratio complicates the systematic optimization of existing GTM processes. With this challenge in mind, the reactor-level kinetic study and system-level techno-economic analysis are implemented to quantitatively investigate the feasibility, sustainability, and profitability of the different process scenarios in the range from 0.2 to 0.6. Herein, three distinct scenarios are proposed: current scenario using steam reforming technology, transitional scenario using CO2/Steam-mixed reforming technology, and future scenario using CO2/O2-mixed reforming technology. As a result, the reactor-level kinetic analysis suggests high CO2/ (CO2+CO) ratios suppress the formation of byproduct dimethyl ether. Nevertheless, the system-level technoeconomic analyses indicate the appropriate CO2/(CO2+CO) ratio (0.3), rather than extreme values, favors energy and exergy efficiency, carbon mitigation as well as cost saving. This study provides deep insights into the role of CO2/(CO2+CO) ratios in GTM processes and offers a scientific foundation for optimizing GTM processes.

Hydrogenation of CO2 to liquid fuel is a crucial technology for e-fuel synthesis in carbon capture, utilization, and storage (CCUS) processes. Designing an efficient catalyst for CO2 direct hydrogenation requires a comprehensive understanding of the active phases and reaction mechanisms. However, the complexity of active phases in Febased catalysts and reaction intermediates in CO2 hydrogenation pose challenges in computational approaches. Herein, we identified the active phase of Fe catalysts for CO2 hydrogenation using density functional theory (DFT) calculations. Based on the scaling relations, we constructed descriptor-based micro-kinetic models for CO2-Fischer-Tropsch synthesis (CO2-FTS) and CO-Fischer-Tropsch synthesis (CO-FTS). The derived volcano plot suggested that Fe-Fe3C surfaces are efficient in both the reverse water-gas shift (RWGS) reaction and Fischer-Tropsch synthesis (FTS). Based on the microkinetic model, 16 alloy surfaces were evaluated, suggesting Cu and Mn as promising promoter candidates. The experimental analysis of Fe-Me-K/AC catalysts (Me = W, Zn, Ni, Co, Cu, Mn, B) revealed that carbidic phase composition was mainly governed by the vacancy formation energy of Me-Fe5C2. In catalytic activity tests, Fe-Cu-K/AC catalyst with a high composition of Fe and Fe3C, exhibited the highest C5+ hydrocarbon yield (18.3 %) among the catalysts. This implies that the promoter's effect on the phase composition is more significant than its impact on intrinsic activity. The proposed microkinetic model and promoter screening approach provides insights into catalyst design for CO2 hydrogenation.

Both indirect CO2 2 hydrogenation (reverse water gas shift (RWGS) followed by CO-based Fischer-Tropsch synthesis (FTS)) and direct CO2-based 2-based FTS were considered for CO2 2 hydrogenation, and a kinetic model for the chain-length distribution of hydrocarbon products was developed. For independent estimation, the kinetic parameters were estimated by fitting the experimental data using powder catalysts under various conditions, mainly including CO/CO2 2 ratios. The contribution of indirect CO2 2 hydrogenation (RWGS followed by CO-FTS) was more favorable than that of direct CO2-FTS, 2-FTS, and CO2 2 conversion and product selectivity were significantly dependent on the temperature and hydrogen fraction. The effectiveness factor was estimated for the pellet-type catalysts, and values less than one validated the existence of mass-transfer resistance. Computational fluid dynamics (CFD) modeling was used to simulate the three-dimensional thermal behaviors of a mini-pilot- scale reactor with a substantially large diameter loaded with a pellet-type catalyst and inert materials. Both a low catalyst loading in the early stage of the reactor and the use of an additional inner cooling tube showed a stable temperature profile, with the peak temperature maintained below 350 degrees C (the critical temperature to prevent the thermal decomposition of chemicals) and fast heating of cold feed in the early stage. The CFD results with no inner tube showed thermal runaway in the second reactor, and the simulation with arbitrarily reduced heat of the reaction (70 % of the actual value) resulted in a peak temperature higher than 410 degrees C. Further quantitative analysis indicated that the no-inner-tube case's reduced heat transfer area per unit volume was responsible for its thermally unstable behavior.

In the context of global carbon neutrality, carbon capture and storage (CCS) technology has become an important transition pathway to decarbonizing coal-fired power plants (CFPP). However, CCS technology has strict requirements for geological storage and the potential risk of CO2 leakage. Meanwhile, the deployment of the CCS technology in the CFPP could drastically reduce plant efficiency. To address the aforementioned issues, a novel carbon capture, utilization and storage (CCUS)-assisted electricity-chemical polygeneration process (i.e., ECPP) was proposed to produce electricity, liquid fuels, and high-calorie synthetic natural gas simultaneously. To reduce the efficiency loss caused by the consumption of internal steam and electricity, heat integration and organic Rankine cycle (ORC) technologies were adopted to fully recover the available waste heat and achieve the cascade utilization of the internal energy. Meanwhile, a detailed techno-economic assessment was conducted to further determine the benefits of the process integration. The results indicated that the application of heat integration and ORC technologies improves plant efficiency by 6 %. Moreover, it also reduces the cost of electricity and CO2 conversion cost by 17 and 15 %, respectively. In addition, compared with the traditional CFPPs retrofitted with CCS technology, the CO2 utilization and waste heat recovery technologies in ECPP enhance net electricity output and plant efficiency by 19 and 33.80 %, respectively. Therefore, the proposed CCUS-assisted ECPP achieves the efficient utilization of the waste CO2, and reduces the efficiency penalty for retrofitting the CFPPs. Overall, the proposed ECPP is an essential alternative for the retrofit of the existing CFPPs, and provides a feasible strategy for establishing a clean and sustainable power polygeneration system.

CO2-to-olefins (CTO) technology has emerged as a worthy solution for green olefin production and greenhouse gas emissions mitigation. However, most of the present researches focus on the development of highperformance catalysts, while few of them devote to the process design and performance evaluation. Hence, this study proposed three candidate CTO processes via methanol-mediated, direct and indirect FTS-based routes. Based on the rigorous modeling and simulation, exergy-based (i.e., exergetic, exergoeconomic, and exergoenvironmental) analyses were conducted to quantify the overall exergy dissipation, economic cost, and environmental impacts. More specifically, we carefully assessed and compared their comprehensive performances from the system-level, and discern the origins and formation of economic cost and environmental impacts from the component level. As a result, the direct FTS-based process has the highest exergy efficiency of 68.65 %, while the indirect FTS-based process and the methanol-intermediated process exhibit the lowest unit exergoeconomic cost and exergoenvironmental impacts of 0.147 $/kW and 38.55 mPts/kW, respectively. In addition, some pertinent optimization suggestions were proposed to enhance the systems' thermodynamic efficiency, economic and environmental benefits. Overall, this study offers crucial insights into the thermodynamic irreversibility, economic viability, and environmental sustainability of the proposed CTO systems, propelling the frontiers of future sustainable olefin production.

The N atom in the nitrogen-doped carbon materials can promote the adsorption and conversion of CO2. In addition, as a bridge between N and Fe, the degree of graphitization of carbon supports significantly affects the electron transfer process.

To produce alternative fuel and reduce CO2 emissions, the CO2-to-methanol (CTM) process is currently considered to be an effective technical pathway. However, the base CTM process suffers from high energy consumption and low carbon efficiency. Therefore, this work proposed an optimized CTM process integrating double-effect distillation, waste heat recovery, and H2 stripping technologies. Compared to the base CTM process, the optimized CTM process significantly enhances the techno-economic-environmental performances. Meanwhile, it realizes zero external heat requirements and negative carbon emissions. In order to quantitatively evaluate the improvements in the process performances, we conducted detailed technical-economic-environmental analyses. From the technical perspective, the energy efficiency and exergy efficiency of the optimized CTM process are 10.28% and 4.84% higher than that of the base CTM process, respectively. From the economic perspective, the methanol production cost in the optimized CTM process is lower by 18.40 $/tonne MeOH compared to the base CTM process. As for the environmental perspective, the GWP of the optimized CTM process is reduced by 336.42 kg CO2-eq/tonne MeOH compared with the base CTM process. In summary, the optimized CTM process offers an energy-efficient, cost-saving, and environment-friendly solution for CO2 conversion.

Concerns about depleted fossil fuels and the climate crisis have intensified the interest in producing biomass-derived methanol. However, the traditional biomass-to-methanol (BTM) process suffers from low carbon conversion ability and serious CO2 emissions caused by the water–gas-shift (WGS) unit. In this study, three novel BTM processes coupled with solid oxide electrolysis, methane pyrolysis, and methane chemical looping technologies are proposed to eliminate WGS unit, and the systematic heat integration is considered to achieve energy cascade utilization. Meanwhile, process performances are comprehensively evaluated to compare the technical, economic, and environmental attractiveness of three novel BTM processes. It is found that compared with the original BTM process, three novel processes significantly improve carbon efficiency by 22%. Meanwhile, CO2 emissions are reduced by 60%. Moreover, the application of methane chemical looping technology is more economical, and the associated net production cost decreases by more than 30%. Additionally, the BTM process coupled with solid oxide electrolysis is more environmentally friendly, whereas the process with methane pyrolysis technology is more exergy-efficient. Overall, the integrated processes have significant application prospects for carbon conversion and mitigation ability as well as economic attractiveness.

Direct hydrogenation of CO2 to liquid hydrocarbons via modified Fischer-Tropsch synthesis represents an appealing and sustainable route for efficient CO2 utilization. However, the selective production of liquid hydrocarbons remains a significant challenge. In this work, we designed a series of carbon-coated K/Fe-C catalysts with various K loadings (ranging from 0 to 8 wt%) that enhance C5+ hydrocarbon selectivity during CO2 hydrogenation. It is found that the 4 K/Fe-C catalyst exhibits the highest C5+ selectivity of 54.78 % at CO2 conversion of 32.40 % and good stability within 100 h time-on-stream. This is attributed to the high dispersion of the Fe nanoparticles and the confinement effect of porous carbon matrix on the aggregation of Fe nanoparticles, resulting in high catalytic activity and selectivity. Meanwhile, the well dispersed K on the porous carbon matrix can reduce the particle size of Fe nanoparticles and promote the production of iron carbide active species for CO2-FTS, thus facilitating the selective formation of C5+ hydrocarbons. Moreover, we also discussed a possible reaction mechanism for the direct hydrogenation of CO2 to C5+ hydrocarbons over the K/Fe-C catalysts. This study provides deep insights into the design of efficient Fe-C catalysts for converting CO2 to liquid hydrocarbons.

In the past decades, Power-to-Liquid (PTL) and Power-to-Gas (PTG) technologies, which utilize the captured CO2 and surplus renewable electricity to produce sustainable fuels and chemicals, have attracted much attention. In our previous study, four PTL/PTG process cases coupled with different water electrolysis technologies (i.e., AWE, PEM, SOEC, and AEM) have been proposed to simultaneously produce syncrude and SNG. To comprehensively examine their technical, economic, and environmental performances, this paper carried out an exergy-based (i.e., exergoeconomic and exergoenvironmental) analysis. Firstly, a Life Cycle Assessment (LCA) was plotted with the material and energy flows data to evaluate the tangible and potential environmental impacts. Secondly, an exergoeconomic and exergoenvironmental analysis that integrate exergy analysis with economic analysis and LCA was suggested to calculate the integrated technical-economic and technical-environmental performances. The formation of exergoeconomic cost and exergoenvironmental impacts in the four cases are illustrated by Sankey diagrams. The results revealed that the case coupled with AEM electrolysis technology has the lowest exergoeconomic product cost and exergovironmental potential emissions. In the certain cases, the components with considerable energy consumption and temperature changes are the main contributors for the total exergoeconomic cost and exergoenvironmental impacts. Regarding the results, this work intends to provide optimization suggestions, aiming at achieving a balance among the better technical and economic performances and less environmental impacts.

Low-carbon olefins, as important platform molecules, are generally produced by limited fossil energy, resulting in massive carbon emissions and intensive energy consumption inevitably. Therefore, it is necessary to develop clean and sustainable alternatives. With this in mind, three low-carbon olefin production processes using waste CO2 and green H-2 were proposed, including the methanol-mediated (Option A) and Fischer-Tropsch synthesis (FTS)-based CO2-to-olefin (CTO) processes. Herein, the FTS-based CTO processes are classified into the direct (Option B) and indirect routes (Option C) without/with the reverse water-gas-shift unit. Meanwhile, rigorous process models were established, and detailed mass and energy balances of three processes were obtained with the aid of the process simulator. Moreover, in order to evaluate the feasibility and compare the differences in process performances of three proposed processes quantitatively, comprehensive techno-econo-environmental assessments of three processes were conducted at the system level. The results indicate that, firstly, from a technical perspective, the FTS-based processes are more competitive than the methanol-mediated process due to their higher energy efficiency (67.93%) and carbon utilization efficiency (84.22%). Secondly, from an economic perspective, the methanol-mediated process has a better economic prospect in the minimum olefin selling price (2527.08 $/tonne C-2-C-4 olefins). Lastly, from an environmental perspective, the methanol-mediated process is more environmentally friendly owing to its lower CO2-eq emissions (61.13 kg CO2-eq/tonne C-2-C-4). Moreover, for two FTS-based processes, the direct route is favorable in energy efficiency and minimum olefin selling price, whereas the indirect route is preferable in the carbon utilization efficiency and environmental impacts. Overall, the study provides novel approaches for the production of low-carbon olefins, and is of significant importance for reducing carbon footprint and achieving carbon neutrality.

Direct hydrogenation of carbon dioxide (CO2) to value-added aromatics can not only provide a sustainable ar-omatics synthesis route but also realize CO2 mitigation. However, it remains a great challenge to identify the optimal surface acidity and regulate the selective formation of aromatics during CO2 hydrogenation. Herein, we designed and prepared a series of K/Fe-Cu-Al@HZSM-5 tandem catalysts, and deeply investigated the effects of zeolite surface acidity on the catalytic performance, by changing the SiO2/Al2O3 ratios of HZSM-5 from 25 to 400. It was found that the surface acidity, especially for the Bronsted acidity, plays a crucial role in the aromatics formation. With an increasing Bronsted acidity from 0 to 290 mu mol/g, the CO2 conversion keeps relatively stable (around 44%), however, the aromatics yield monotonously increases from 0.9 to 12.8%, indicating a distinct correlation with the Bronsted acidity. Among the obtained aromatics, the majority ones are C6-8 light aromatics, accounting for c.a. 30-60% within time on stream (TOS) of 24 h, but their proportion tends to gradually decrease with TOS, probably due to the catalyst deactivation by coking. Moreover, the possible reaction pathways for aromatics formation over the prepared K/Fe-Cu-Al@HZSM-5 tandem catalysts were also proposed.

Although iron-based catalysts are effective for long-chain hydrocarbon formation during the hydrogenation of CO2, they easily undergo deactivation. Thus, the deactivation behaviors of Fe-based catalysts supported on active carbon were investigated using various promoters. Ten metals were selected as promoters, and the resulting catalytic activities and selectivities over the course of 100 h were evaluated. Catalyst deactivation was primarily caused by changes of active phase and active crystallite size, namely active site transitions. Although the oxidation of Fe carbide is an unavoidable process, this can be alleviated by increasing the crystallite size to expose greater numbers of active sites and compensate for the deactivation process. The Cu-modified catalyst exhibited the highest CO2 conversion and C5+ yield, but was easily deactivated. In contrast, the Zn-modified catalyst exhibited stable activity, good C5+ yield, and high olefin/paraffin ratio by inhibiting oxidation and exhibiting a large increase in the active crystallite.

With the emergence of numerous CO2 chemical conversion technologies to simultaneously reduce CO2 emissions and produce value-added products, it is of great importance to compare their difference and select the most sustainable routes for future development. This study quantitatively evaluated the sustainability performances of 21 alternative CO2 conversion technologies from economic, technical, and environmental perspectives and developed a novel Multi-criteria Decision-making (MCDM) model to prioritize the alternatives. To cope with the external and internal uncertainties during the decision-making, Interval-Rough Numbers (IRNs) were firstly used to deal with subjective vagueness and information incompleteness involved in the group judgements unavoid-ably. Secondly, DEMATEL-ANP was employed based on IRNs to specify the correlation type and degree among diverse criteria for determining the global weights accurately. Lastly, a Vector-based Algorithm method was applied to measure the alternatives' overall performance and figure out the final ranking scores of sustainability. The results revealed that CO2 to methane, urea, methanol, dimethyl ether, and acetic acid were the top five promising conversion technologies with the highest R&D priority over the next decades from a sustainability perspective. Moreover, a detailed sensitivity analysis of criteria weights was conducted to scrutinize the effec-tiveness of the ranking results and to validate the reliability of the new proposed MCDM model. Furthermore, in consideration of the complexity of future technological advance, market transformation, economic and social trends, this life cycle sustainability decision-support framework for CO2 conversion technologies provides a well-informed benchmark to support the screening and selection of candidate technologies including both the existing and emerging processes, and strategically explore the development opportunities and limits under uncertainties.

To achieve efficient utilization of CO2 and produce clean alternative fuel, nowadays, CO2-to-DME (CTD) technology is regarded as a feasible and promising solution. Considering that there is no consensus on the techno-economic performances of the different CTD processes, it is necessary to conduct a comprehensive and systematic comparison of the existing and emerging CTD technologies and to deeply explore the influence of the process integration on technical feasibility and economic profitability. In this study, we proposed four CTD processes via different routes, namely purified methanol-mediated (Case 1), water-containing methanol-mediated (Case 2), CO-mediated (Case 3) and direct CO2 hydrogenation routes (Case 4). The rigorous system modelling and comprehensive comparison of the process performances of four cases were implemented. From the technical perspective, Case 4 has the highest energy efficiency (77.42%), exergy efficiency (88.46%), and net CO2 mitigation rate (67.71%). From the economic perspective, Case 2 has the lowest total product cost (1327.14 $/tonne DME), whereas Case 4 has the lowest net CO2 mitigation cost (589.34 $/tonne CO2). Moreover, to further enhance the system performance of Case 4, we also proposed effective improvement measures for process optimization, which shows that the net CO2 mitigation rate is enhanced by 1.94%, while the net CO2 mitigation cost is reduced by 19.79 $/tonne CO2.

CO2-to-DME (CTD) technology has been considered as a worthy solution for waste CO2 upcycling and green DME production. Faced with various emerging CTD routes with pros and cons, it is important to systematically assess and compare their attractiveness and difference, and identify the most sustainable technologies for further development and improvement. Thus, the present study proposed four promising CTD routes (i.e., two-step routes using high- and medium-concentration methanol as intermediates, and one-step routes with and without RWGS reactions) and developed a multi-criteria sustainability assessment and decision-making framework for alternative routes comparison and prioritization. Eleven KPIs were considered from technical, economic, and environmental perspectives to evaluate system sustainability. Exergoeconomic and exergoenvironmental analysis were conducted to pinpoint the location, magnitude, and sources of system inefficiencies from the component level. A TOPSIS method was employed to integrate multidimensional performances and present an informed decision-making process. As a result, all the alternative routes are sustainable for DME synthesis, and therein the one-step route without RWGS reaction always ranks as the most competitive choice through rigorous sensitivity analysis. Moreover, this work provides a strategic decision support for assessing the trade-offs involved in existing and emerging sustainable CO2 upcycling technologies towards carbon neutrality.

Power-to-liquid (P2L) and Power-to-Gas (P2G) processes are considered as sustainable pathways to mitigate climate change. In both P2L and P2G processes, H2 production via water electrolysis has received widespread attentions, including PEM, AEM, SOEC and AWE technologies. Based on the preceding technical study on four P2L/P2G hybrid processes composed of above-mentioned water electrolysis technologies, a systematic study of P2L/P2G processes and economic analysis were conducted to quantitatively evaluate their economic performances in terms of total production cost (TPC) and net CO2 reduction cost (CRC). The P2L/P2G process coupled with SOEC technology has the lowest TPC of 204 M$/year, while that coupled with AEM technology has the lowest net CRC of 274 $/tonne CO2. Moreover, we further proposed nine process scenarios for P2L/P2G processes using grey, blue, and green H2, and compared their process performances in terms of TPC and global warming potential (GWP). The P2L/P2G process via water electrolysis using wind electricity reduces GWP by 61.50%, whereas its TPC is 1.39 times higher than that with coal gasification due to the relatively high production cost. It is anticipated that a significant cost saving in the water electrolysis units is possible in the future, which will definitely improve the profitability of P2L/P2G process.

Recently, Power-to-Liquids (PtL) and Power-to-Gas (PtG) technologies have been regarded as promising pathways for renewable energy storage and CO2 mitigation. Herein, we newly proposed two PtL/PtG hybrid processes (Cases A and B) by integrating the Fe-based Fischer-Tropsch (F-T) synthesis and olefin oligomerization, to further enhance the production of value-added liquid hydrocarbons. The process modelling and case study were implemented to evaluate their process performances by using Aspen Plus. In addition, the effects of different feeding conditions (i.e., CO/CO2 feeding) and process configurations (i.e., F-T synthesis only or two-stage reactor) were also comparatively analyzed. It is found that both Cases A and B are efficient technologies for converting CO2 into value-added hydrocarbons, and Case A is found to be more beneficial in the aspects of the carbon and thermal efficiencies, and net CO2 reduction. While, Case B is competitive in producing high-value liquid hydrocarbons. Moreover, the options of CO2 feeding and two-stage reactor are more preferable than the options of CO feeding and F-T synthesis only, and both Cases A and B are more competitive in the aspects of syncrude production, thermal efficiency, and CO2 reduction, as compared to the Base cases 1–3.

Mixed Fischer-Tropsch synthesis (FTS) catalysts and HZSM-5 (HZ5) have received attention as bifunctional catalysts that directly convert syngas into value-added aromatic monomers. However, both low selectivity of aromatics and severe deactivation remain challenges. Here we report a simple method for obtaining selective aromatics from syngas by tuning the distribution of hydrocarbon intermediates on K/FeMn. We prepared K/FeMn catalysts with a varying Mn/(Fe+Mn) wt.% to demonstrate the effect of the hydrocarbon distribution as intermediates of aromatization on HZ5. The C6-C10 distribution was increased by addition of up to 60 wt.% of Mn promoter due to the improved dispersion of Fe 7 C 3 and alkyl insertion of MnO. At 340 o C under 20 bar, 97.2% CO conversion and 39.8% aromatics selectivity were achieved by using a physically mixed catalyst of K/FeMn with Mn/(Fe+Mn) 60 wt.% and HZ5 with an optimization of the FTS-derived C6-C10 olefin yield as efficient intermediates in Syngas to Aromatics (STA).