《1 Engineering research fronts》

1 Engineering research fronts

《1.1 Trends in Top 11 engineering research fronts》

1.1 Trends in Top 11 engineering research fronts

The Top 11 engineering research fronts as assessed by the Field Group of Chemical, Metallurgical, and Materials Engineering are shown in Tables 1.1.1 and 1.1.2. “Design and process optimization of low-carbon and energy-saving metallurgical reactors”, “integrated monolithic electrodes for highly efficient electrochemical energy storage”, and “efficient preparation and catalytic mechanism of super-dispersed single-atom alloy catalysts” were recommended by experts directly. The other fronts were chosen by a panel of experts using core-paper statistics provided by Clarivate. Topics on “electrocatalysis, monoatomic catalysis and intrinsically safe battery” are still hot topics, with more than 200.00 citations per paper (Table 1.1.1). However, the annual number of core papers for all topics is decreasing (Table 1.1.2).

(1) Renewable energy-driven bioconversion of carbon dioxide to chemicals, fuels, and materials

Biological carbon dioxide (CO₂) sequestration, which is a clean and highly efficient technique, is indispensable for realizing carbon peak and carbon neutrality goals. Renewable energy-driven bioconversion of CO₂ takes full advantage of biological CO₂ sequestration. In this technique, renewable energy, such as light or electricity, is used as a substitute for chemical energy to provide energy and reducing equivalents for biological carbon sequestration pathways that produce chemicals, fuels, and materials. To date, relevant research has focused on in vitro multi-enzyme-based CO₂ sequestration and whole cell-based CO₂ sequestration

《Table 1.1.1》

Table 1.1.1 Top 11 engineering research fronts in chemical, metallurgical, and materials engineering

《Table 1.1.2》

Table 1.1.2 Annual number of core papers published for each of the Top 11 engineering research fronts in chemical, metallurgical, and materials engineering

driven by light/electricity. The main goals have been ① the construction of new biological carbon sequestration pathways, ② the design and preparation of new biocompatible photo- or electrocatalytic materials, and ③ the adaptation of biocatalytic modules and photocatalytic modules. Bioconversion of CO₂ driven by renewable energy is a green process with a green raw material and green product. However, the overall energy efficiency of this technology is unsatisfactory, and there are still some bottlenecks in industrial applications. For future advances, the following directions are suggested: in situ characterization techniques for clarification of energy exchange mechanisms between biocatalysts and artificial catalysts to deepen the understanding of the coupling processes; core technologies for the rational design of enzymes and microbial cell factories to produce high-quality biocatalysts with high efficiency and adaptability and to further increase productivity; and advanced reactors and separation media to establish an integrated equipment and technology system for raw material supply, process intensification, and product separation engineering.

(2) Chaotic nonlinear enhancement technology of metallurgical flow field

In metallurgical processes, the interplay of flow, heat/mass transfer, and reaction involves intricate nonlinear dynamic mechanisms and multi-scale spatiotemporal characteristics. These features pose formidable challenges for the design, optimization, and operation of metallurgical reactors. Chaotic nonlinear enhancement of metallurgical flow field integrates knowledge from fluid dynamics, chaos theory, and nonlinear science. This aims to uncover the coupling and scale-up theory governing the interplay of flow, heat/mass transfer, and reaction in metallurgical reactor processes. Inherent connections between chaotic characteristics of the fluid phase, destabilization of intermediate steady flow structures, and enhancement through chemical chaos are elucidated. By constructing a correlation model between chaotic flow and temperature field-flow uniformity, the relationship between chaotic flow and temperature field-flow uniformity is precisely delineated. Leveraging the coupling mechanism between chaotic mixing characteristics, field uniformity, and the formation, transport, and conversion of multi-scale flow structures, this technology enhances heat and mass transfer efficiency by modulating the chaotic behavior of bubble clusters. This technique offers a fresh regulatory approach for topological coupling of complex multiphase flow patterns in metallurgical furnaces, and effectively addresses the challenge of accurately describing the cooperative nature of the flow field-temperature field during the enhancement process and intensified heat transfer via bubble cluster agitation. This theory is promising for further development of extreme and unconventional metallurgy, large-scale equipment, and intelligent metallurgy.

(3) High-performance electrocatalysts and electrolysis systems for CO₂ conversion and utilization

In the overall energy and environmental system, green and efficient conversion and utilization of CO₂ is important for realizing efficient conversion of low-carbon energy. Among the available methods, CO₂ capture, utilization, and storage technology has gradually become the key technology to cope with climate change and achieve the goals of carbon peak and carbon neutrality. Currently, green electricity provided by renewable energy sources such as solar energy and wind energy drives the catalytic conversion of CO₂. This solves the problem of excessive CO₂ emissions and realizes the direct conversion of intermittent electric energy into chemical energy, which is important for achieving carbon balance and optimizing energy consumption. The research on CO₂ electrocatalytic conversion has focused on the following aspects: ① the use of in situ spectroscopy to monitor key intermediates in the CO₂ reduction reaction (CO₂RR), and construction of the reaction network in the catalytic conversion process of CO₂ using theoretical calculations; ② design and development of high-performance electrocatalysts, regulation and optimization of the catalyst structure, and study of the structure–activity relationship between the catalyst and CO₂RR performance; and ③ design and optimization of the electrode structure and adjustment of the entire electrolytic reactor to control the operation of the reaction system and use its modular characteristics to achieve regulation and optimization so that each index meets the requirements of industrial application. Further development of CO₂RR requires improvement of the long-term continuous operation stability of the electrocatalyst and expansion of the scale of the CO₂ electrolyzer. Additionally, the target for practical application, the economics of the product, market supply, and demand need to be determined. The final product separation and recovery costs of excess CO₂ feedstock gas and electrolyte also require further design management.

(4) In situ molecular/atomic scale characterization of heterogeneous catalysts under reaction conditions

The structure and surface/interface properties of a catalyst are directly related to the catalytic performance and provide direct evidence for modeling. The active sites of catalysts and coordination environment change dynamically during catalytic reactions, and their spatiotemporal evolution provides vital information for the rational design of heterogeneous catalysts. The characterization of these surface/interface structures and chemistry, especially in situ characterizations under relevant reaction conditions, is important for elucidating the mechanisms. State-of-the-art in situ characterization techniques for heterogeneous catalysts at the molecular/atomic scale under various reaction conditions include in situ electron/scanning probe microscopy, in situ infrared/Raman spectroscopy, and X-ray photoelectron/absorption spectroscopy. Research has focused on ① revealing the structural active sites of specific reactions through in situ atomic-scale observation of dynamic structure changes of heterogeneous catalysts for rational design of atom-precise new catalysts; ② revealing the chemisorption and dissociation of molecules at the catalyst surface and determining the intermediates and their spatiotemporal distributions to elucidate the entire reaction route; and ③ combining multiple characterization methods and model catalysts to relate structural and chemical active sites for critical chemical reactions.

(5) Design and process optimization of low-carbon and energy-saving metallurgical reactors

In the process of size amplification, structure adjustment, and process optimization of super-large or special smelting equipment, a lack of a theoretical basis often leads to equipment amplification distortion, operation instability under changeable working conditions, and amplification mismatch between the theoretical model and practical equipment. This can lead to high energy consumption of the metallurgical reactor and smelting process. The operation process involves complex concentration-melt- rich oxygen jets, electric–magnetic–flow–heat–particles–components multi-fields, cooperative coupling between microscopic response, mesoscopic motion, and macroscopic operation, and requires size amplification in the design of low carbon smelting equipment and fine optimization for processes of dynamic test and simulation methods. Future research should focus on developing new methods for quantitative visual characterization of the flow field in a cold simulated multiphase system. For the cold state test model of large equipment using similarity theory, visual analysis techniques such as high-speed dynamic recording of flow field characteristics and PIV (particle image velocimetry), quantitative measurement techniques such as image analytical processing, mixing time determination, and chaos mathematical analysis can be used to realize quantitative characterization of the mixing degree of the nonlinear flow field. Furthermore, studies should look at the multi-field coupling mechanism of electric– magnetic–flow–heat–particles–components in gas–liquid–solid multiphase systems, including various transfer processes and metallurgical chemical reaction rules in actual metallurgical reactors. The results could be used to simulate and analyze the cooperative coupling laws of single and multiple associated reactors to optimize and improve the existing process and develop new carbon energy-conserving metallurgical processes and reactors.

(6) Rational design and fabrication of special alloys for cryogenic environments

Governments around the world are focusing on innovation and development of equipment in clean energy, aerospace, and other areas. Key components in the equipment often experience cryogenic environments, such as superconducting coils of magnetic confinement fusion reactors (~4 K), aerospace liquid oxygen/liquid hydrogen engines (~20 K), and wind tunnels with high Reynolds numbers (~77 K). This results in the need for exceptionally stringent requirements for the involved special alloys. Currently, special alloys in cryogenic environments face various challenges including inferior performance, ambiguous regulation mechanisms for their microstructures and properties, and immature preparation processes. These challenges largely limit improvements in aircraft manufacturing technology and the utilization of clean energy. There are many scientific problems that need to be solved in the rational design and preparation of special alloys for cryogenic environments. First, precise control of phase stability is required during cryogenic service. This mainly includes the mechanism of the austenite stacking fault energy in special alloys under cryogenic conditions, the effective control of phase stability, and the role of their interactions in different cryogenic properties, which in turn guides the alloy composition design and fabrication process. Second, systematic study is required for the multiphase microstructure evolution behavior and the strengthening and toughening mechanism during the integrated processing of melting–forging/rolling–heat treatment–welding for cryogenic special alloys. This includes the principle of forward/reverse phase transformation, alloy element partitioning, precipitation control, and cryogenic deformation. The microstructure–property relationships need to be determined among typical processing routes, multiphase microstructure components, and mechanical properties. Third, in complex cryogenic environments, it is necessary to study the failure modes and mechanisms under multi- field coupled service conditions with highly corrosive media over wide temperature ranges and under cyclic loading. This should include the mutual matching mechanism of multiple mechanical and physical properties at low temperatures, cryogenic failure behaviors under the coupling of thermal fatigue, wear, and corrosion, and the relationship between service performance and failure mechanisms. The results could be used to provide guidance for alloy design and fabrication process optimization of the cryogenic special alloys.

(7) Integrated monolithic electrodes for highly efficient electrochemical energy storage

Lithium-ion batteries occupy the majority of the market in the field of electrochemical energy storage. However, their present energy densities and power densities still need to be improved to meet growing social development. It is important to develop a new generation of lithium batteries with high specific energy, high power density, high stability, long life spans, high safety, and low cost. The key to achieving this goal is to have a clear understanding of the electrochemical energy storage mechanism of each involved active electrode material, and to carry out system design at the level of cell components and the overall electrode architecture. Therefore, research has focused on the design and fabrication of integrated monolithic electrodes with various compositions and structures. The developed electrodes will have excellent ion–electron mixed conductivities and could eliminate the use of inactive components such as binders. They will also have a suitable pore structure to maintain high structural stability during the charge–discharge process. To date, the research in this area has focused on the following aspects: advanced electrode structure design, simple electrode fabrication strategies, design and selection of current collectors and loading of active components, increasing the loading mass of active materials in area and volume, improving the conductivity of the overall electrode, matching of cathodes and anodes (construction of a full cell), development of flexible or thick electrodes, and determining the working or electrochemical reaction mechanism of the electrode. The structural design and simple fabrication of integrated monolithic electrodes with high active material loads are technical bottlenecks that need to be solved in this field.

(8) Research on high-strength high-toughness and low-density steel

Low-density steel, also known as lightweight alloy steel, is a lightweight material that reduces the density of the alloy by adding lightweight elements such as Al, Mn, and C. Research has shown that adding Al at a mass fraction of 1% can reduce the density of the steel by 1.3%. Low-density steel has broad application prospects in lightweight and safe service in vehicles, ships, aerospace and military fields. At the beginning of the 21st century, a study by the Max Planck Society in Germany showed that Fe–Mn–A1–C high-strength, high-toughness, and low-density steel had excellent potential for mass reduction, which was a driver for research on the use of low-density steel in automobiles. In 2015, POSCO in Republic of Korea trialed industrial production of rolling low-density steel, and in 2022, Xingcheng Special Steel in China trialed industrial production of high-strength, high-toughness, and low-density steel plates. Additionally, companies such as JFE and Nippon Steel in Japan, ThyssenKrupp in Germany, and Baowu and Ansteel in China have conducted research on and trialed production of low-density steel. However, further development and application of high-strength, high-toughness and low-density steel are restricted, due to factors such as manufacturing costs, surface quality and application technology. To date, research on high-strength, high-toughness, and low-density steel has focused on Fe–Mn–Al–C low- density steel. The main research directions include single ferrite steel, ferrite-based dual-phase steel, austenite-based dual-phase steel, and austenitic steel. There are still many scientific issues that need to be studied for the composition design, microstructure control, and service performance of Fe–Mn–Al–C low-density steel.

(9) Efficient preparation and catalytic mechanism of super-dispersed single-atom alloy catalysts

Single-atom alloy catalysts (SAACs) are usually prepared by dispersing a single atom of an active metal (typically a precious metal) in a second metal support (commonly a non-precious metal). SAACs have attracted attention in recent years because they have high utilization efficiency of noble metal atoms, high catalytic activity, and high selectivity. Since Sykes and colleagues proposed the concept of SAACs [Pd1/Cu(111)] in 2012, scientists worldwide have explored various preparation methods of SAACs and gradually applied them to catalytic reactions such as fuel cells, electrolytic water, selective hydrogenation, and CO oxidation. To date, research on SAACs has focused on three aspects. First, exploring facile and efficient strategies to prepare SAACs with high atom pairing ratios and to precisely adjust the interactions between the active site and surrounding atoms. Second, revealing the structure–activity relationship between single-atom alloy structures and catalytic performance and the catalytic mechanism at the atomic level using in situ fine structure analysis and theoretical calculations. This could be used to provide a theoretical basis for the rational design of functional SAACs. Third, developing macro-preparation process for SAACs with adjustable noble metal loading, which will bridge the gap between fundamental research and industrial application. Because of their low noble metal loading and excellent catalytic activity, selectivity, and stability, super-dispersed SAACs will be key for the development of industrial catalysis.

(10) Selective confined mass transport membrane for ion separation

Ion-selective separation is an important area of membrane separation technology. This technique has been applied to lithium extraction from salt lakes, saltwater purification, high-salinity wastewater resource recovery, and flow batteries. The performance of traditional polymer membrane materials is restricted by the trade-off effect, where flux and selectivity cannot be improved simultaneously. Confined mass transfer membranes, which can be constructed using artificially engineered channels at the sub- nanometer scale, have unique mass transfer characteristics and are promising for use in this area. Currently, research on selective ion-transport membranes is divided into two areas. The first involves the fundamental exploration of separation mechanisms to explore the factors influencing mass transfer dynamics and selectivity at the microscale, such as the channel geometric structure and interfacial physicochemical properties. The results from this could aid in membrane design. The second involves the design of membrane materials to achieve ultrafast mass transfer using materials with different sizes, functional groups, and interfacial charges, such as COFs and MOFs. Future research will look at in situ visualization of confined channels to establish an effective connection between ideal mass transfer models and the actual performance of separation membranes. This will be achieved through the manufacture of confined transport membranes with high mass transfer rates and selectivity, the transition from laboratory-scale specifications to large-scale production, and realization of industrial development.

(11) Intrinsically safe battery systems for renewable energy storage

Large-scale energy storage stations have strict requirements for battery safety. An intrinsically safe battery is one with an inner safety mechanism, which can improve the safety performance in the internal structure, and materials that can effectively prevent and control dangerous situations such as thermal runaway, explosion, and leakage. Current research in the field of intrinsically safe batteries is creating new breakthroughs. Scientists are committed to developing new materials and optimizing the battery structure to improve the intrinsic safety performance and electrochemical performance of batteries, for example, by the addition of flame retardants to effectively inhibit the combustion of electrolytes, development of intrinsic flame-retardant polymer electrolytes to improve the safety of solid-state batteries, and suppression of lithium dendrite to improve the safety of lithium metal anodes. Research on intrinsically safe batteries has focused on the following aspects: improving the electrochemical stability to prevent side reactions, electrolyte decomposition, or instability of electrode materials during charging and discharging; improving the thermal safety of batteries in high- temperature environments by developing non-flammable (or flame-retarding) battery materials and upgrading the battery thermal management system to prevent overheating from causing battery runaway, combustion, or explosion; improving the mechanical stability of the battery by addressing external impact and internal stress of the battery to avoid safety hazards such as battery rupture or an internal short circuit; and replacing the traditional organic electrolytes with solid electrolytes or aqueous electrolytes to improve the safety and stability of the battery and solve the problems of combustion and leakage of organic electrolytes.

《1.2 Interpretations for three key engineering research fronts》

1.2 Interpretations for three key engineering research fronts

1.2.1 Renewable energy-driven bioconversion of carbon dioxide to chemicals, fuels, and materials

Many countries and regions have development strategies for green biorefineries. The 14th Five-Year Plan in China highlights that deep integration of the energy and manufacturing industries with biotechnology will be required to establish a green, low- carbon, and non-toxic circular economy. The Bold Goals for U.S. Biotechnology and Biomanufacturing plan is to achieve gigaton- level CO₂ fixation through bioconversion within the next 9 years at a cost of less than $100 per metric ton. The use of renewable energy to drive the process of bioconversion of CO₂ to chemicals, fuels, and materials reduces carbon emissions, which is a focus for biorefineries. This will lower human dependence on fossil energy to trigger a change in industrial patterns and facilitate the transition to a green economy. Since third-generation biorefineries were proposed in 2020, research on biological carbon sequestration coupled with photocatalysis and electrocatalysis has developed rapidly to achieve carbon peak and carbon neutrality goals. Various pathways and mechanisms have been developed. Biocatalysts can directly take up electrons provided by photo- and electrocatalysts for CO₂ sequestration, and use formic acid, acetic acid, methanol, and other primary products of CO₂ reduction for fermentation. Enzyme engineering and synthetic biology has rapidly progressed and expanded the product spectrum of biological carbon sequestration driven by renewable energy. A series of products, including raw material chemicals such as l-lactic acid, dihydroxyacetone, glycolic acid, and biodegradable plastics such as PLA and PHA, can be produced with CO₂ as the only carbon source. However, compared with traditional methods conducted under high temperature and pressure, there is an efficiency bottleneck for the use of renewable energy to drive biological carbon sequestration. The main solutions to this are development of highly active enzymes and strains and rational design of efficient biological pathways for carbon sequestration; improvement of the utilization of renewable energy and development of photo- and electrocatalysts with bioaffinity and low toxicity; and optimization of the thermodynamic and kinetic adaptation of artificial modules and biocatalytic modules, or decoupling of these modules to ensure optimum efficiency.

The main countries with the greatest output of core papers in recent years on “bioconversion of carbon dioxide to chemicals, fuels, and materials driven by renewable energy” are shown in Table 1.2.1, and the main institutions are shown in Table 1.2.2. The main contributor to these core papers is China (41.3% of the total), followed by the USA, India, Republic of Korea, and Germany (all > 10% of the total). The main institutions in China are Chinese Academy of Sciences and Tianjin University. Figures 1.2.1 and 1.2.2 show the collaboration network among major countries and among major institutions. Scientists have established extensive global collaborations in this field. China’s largest collaborator is the USA. Among the cited core papers, China accounted for 52.02% of the total (Table 1.2.3 and 1.2.4). Among the top ten major producing institutions of the citing papers, all, except for King Abdulaziz University, were Chinese universities or institutes. These institutions included Chinese Academy of Sciences, Jiangsu University, and Tsinghua University.

Renewable energy-driven bioconversion of CO₂ to chemicals, fuels, and materials has developed rapidly in recent years. A roadmap for the engineering research front of “renewable energy-driven bioconversion of carbon dioxide to chemicals, fuels, and materials” is shown in Figure 1.2.3. The key problem with coupling artificial devices that transform renewable energy with biocatalysts is the coupling mechanism. In future studies, it is important to develop techniques to identify the interaction mechanism between artificial devices and biological components. This will promote the development of new and efficient systems and new models. Biocatalysts are central to this process. Progress in the development of robust and efficient industrial enzymes and industrial strains will determine the industrialization process for biological carbon sequestration driven by renewable energy. This will speed

《Table 1.2.1》

Table 1.2.1 Countries with the greatest output of core papers on “renewable energy-driven bioconversion of carbon dioxide to chemicals, fuels, and materials”

《Table 1.2.2》

Table 1.2.2 Institutions with the greatest output of core papers on “renewable energy-driven bioconversion of carbon dioxide to chemicals, fuels, and materials”

《Figure 1.2.1》

Figure 1.2.1 Collaboration network among major countries in the engineering research front of “renewable energy-driven bioconversion of carbon dioxide to chemicals, fuels, and materials”

《Figure 1.2.2》

Figure 1.2.2 Collaboration network among major institutions in the engineering research front of “renewable energy-driven bioconversion of carbon dioxide to chemicals, fuels, and materials”

《Table 1.2.3》

Table 1.2.3 Countries with the greatest output of citing papers on “renewable energy-driven bioconversion of carbon dioxide to chemicals, fuels, and materials”

《Table 1.2.4》

Table 1.2.4 Institutions with the greatest output of citing papers on “renewable energy-driven bioconversion of carbon dioxide to chemicals, fuels, and materials”

《Figure 1.2.3》

Figure 1.2.3 Roadmap of the engineering research front of “renewable energy-driven bioconversion of carbon dioxide to chemicals, fuels, and materials”

up considerably with application of computer technology, such as big data and artificial intelligence, and advanced physical and chemical technology to the screening, modification, and design of industrial enzymes and industrial strains. Technical autonomy of core enzymes and core strains will be achieved in the next few years. Research on advanced industrial reactors should be intensified to achieve real-time monitoring, precise regulation, and efficient separation of CO₂ from various fuels and chemicals according to production needs. This will result in establishment of targeted and efficient production routes.

1.2.2 Chaotic nonlinear enhancement technology of metallurgical flow field

Metallurgical reactors, which are used as reaction vessels in the metallurgical industry, play a pivotal role in industrial processes. These reactors provide a space for intricate multiphase mixing and reaction systems, encompassing the flow, mixing, reaction, heat transfer, and mass transfer of gas, solid, and liquid phases. They serve as a convergence point for micro-scale reactions and macroscopic processes. The metallurgical flow field, functioning as a conduit for energy and mass transfer, has a decisive influence over the synergy of these three domains and the overall system performance. Over the years, significant advancements in measurement and data acquisition techniques for metallurgical reaction systems have greatly enhanced the analytical capabilities of metallurgical flow fields under specific conditions. This progress has contributed to a deeper understanding of the intricate chemical processes involved. However, the design, optimization, and operation of these fields are still heavily reliant on empirical data. The chaotic nonlinear enhancement technology of metallurgical flow represents a cutting-edge research direction in the field of metallurgical science and engineering. This technology integrates knowledge from fluid dynamics, chaos theory, and nonlinear science. Its primary aim is to optimize the behavior of metallurgical flow fields to enhance production efficiency.

Metallurgical multiphase flow is a typical nonlinear process that deviates from equilibrium. It encompasses numerous complex nonlinear dynamic mechanisms and exhibits spatiotemporal cross-scale coupling characteristics. This leads to a lack of synergy between mixing, heat/mass transfer, and chemical reaction processes in metallurgical reaction systems, which poses challenges for effective control, enhancement, and engineering upscaling. The core direction of this field focuses on the synergistic evolution of continuous and dispersed phase topological structures in multiphase systems within metallurgical reactors, the interaction of chaotic flow mixing characteristics with multi-physics fields, and their correlation with transfer performance. The research pathway for chaotic nonlinear enhancement of metallurgical flow is as follows. First, chaos theory is used to describe the multiphase nonlinear systems in metallurgical processes, and rapid inter-phase heat and mass transfer is achieved via chaotic enhancement to accelerate chemical reaction rates. Second, the synergistic coupling of multi-physics fields, including flow, temperature, and composition fields, is realized, which enables effective control of the flow distribution. Third, through the enhancement of the synergy and uniformity of flow-transfer-reaction processes, efficient and uniform mixing is achieved along with intensified heat and mass transfer. This forms the theoretical foundation for the enhancement of metallurgical processes and optimization of reactors.

The major contributors to the engineering research front on “chaotic nonlinear enhancement technology of metallurgical flow field” in recent years are detailed in Table 1.2.5 for countries and Table 1.2.6 for institutions. Among the countries, China holds the lead position, followed by Iran. Among the institutions, the Islamic Azad University ranks first, while China’s Xi’an Jiaotong University, Shanghai Jiao Tong University, and the Chinese Academy of Sciences also rank highly. The collaborative network among the main countries and institutions is illustrated in Figures 1.2.4 and 1.2.5. China occupies a central position in this collaborative network, forming partnerships with multiple countries, and notably has a prominent collaboration with Pakistan. Pakistan is an important node in the network as well, and cooperates with all countries except for the UK and Singapore. Collaborations between institutions are tightly interconnected within Asia, with the Islamic Azad University holding a central position in the collaborative network and partnering with multiple institutions. As indicated in Table 1.2.7, China has the highest number of core paper citations, with 2 490 citations accounting for 26.51% of the total. China is the leader for both the core paper count and cited core paper count, which highlights the advanced position of Chinese scholars in this field. This indicates that Chinese scholars are at the forefront of research in this domain and are keeping abreast of the dynamics in this cutting- edge field.

Chaotic nonlinear enhancement of metallurgical flow involves using chaotic nonlinear theory to study the mixing mechanism of multiphase flow in metallurgical processes and analyzing the formation, transport, and transformation of multi-scale flow structures. To date, because of limitations in experimental measurement techniques and the development of multi- scale simulation methods, research on chaotic flow in extreme and unconventional metallurgy and the scaling up of large- scale equipment remains limited. Moreover, this research direction involves the intersection of multiple disciplines, including metallurgy, fluid dynamics, and physics. There are three future research directions (Figure 1.2.6). First, research on chaotic flow enhancement in extreme and unconventional metallurgical reaction fields by advancing chaotic flow enhancement under extreme and unconventional metallurgical process conditions, involving electric, magnetic, and thermal stress fields. This will break down interdisciplinary barriers and enhance the systematic and universal aspects of nonlinear chaotic theory. Second, research on mechanisms and criteria for amplifying chaotic flow in super-large metallurgical smelting equipment by overcoming the mechanisms and criteria for chaotic flow amplification in metallurgical flow fields and addressing issues arising from the lack of theoretical guidance in the amplification of super-large smelting equipment, including distortion, operational instability, and process mismatch. Third, research on metallurgical flow field chaos nonlinear enhancement technology using machine learning by constructing metallurgical flow field nonlinear enhancement models using machine learning to overcome the complex coupling mechanisms of various factors in metallurgical processes. This will strengthen the intelligent development of metallurgical systems through software and hardware using machine learning.

《Table 1.2.5》

Table 1.2.5 Countries with the greatest output of core papers on “chaotic nonlinear enhancement technology of metallurgical flow field”

《Table 1.2.6》

Table 1.2.6 Institutions with the greatest output of core papers on “chaotic nonlinear enhancement technology of metallurgical flow field”

《Figure 1.2.4》

Figure 1.2.4 Collaboration network among major countries in the engineering research front of “chaotic nonlinear enhancement technology of metallurgical flow field”

《Figure 1.2.5》

Figure 1.2.5 Collaboration network among major institutions in the engineering research front of “chaotic nonlinear enhancement technology of metallurgical flow field”

《Table 1.2.7》

Table 1.2.7 Countries with the greatest output of citing papers on “chaotic nonlinear enhancement technology of metallurgical flow field”

《Table 1.2.8》

Table 1.2.8 Institutions with the greatest output of citing papers on “chaotic nonlinear enhancement technology of metallurgical flow field”

《Figure 1.2.6》

Figure 1.2.6 Roadmap of the engineering research front of “chaotic nonlinear enhancement technology of metallurgical flow field”

1.2.3 High-performance electrocatalysts and electrolysis systems for CO₂ conversion and utilization

The use of renewable energy to drive electrochemical reduction of CO₂ to produce high value-added chemicals provides an effective way to solve the energy crisis and environmental problems. In recent years, research on the development of electrocatalyst materials for CO₂ reduction has made great progress in terms of selectivity, efficiency, and reaction rate, and is moving towards practical applications. Electrochemical reduction of CO₂ can be used to produce various chemicals, such as alcohols, oxygenates, syngas, and olefins, on a large scale. The shift to renewable energy could greatly reduce CO₂ emissions.

Because of its high thermodynamic stability, CO₂ is difficult to activate. Additionally, it is difficult to generate high value- added C2+ products through C–C coupling. Recently, significant progress has been made in the design of highly active or highly selective electrocatalysts and the mechanism of CO₂RR. There are three main areas of focus in current research.

First, design and controllable preparation of highly efficient electrocatalysts through control of the crystal surface, morphology, and surface electronic structure to improve the CO₂RR activity, selectivity, and stability. Second, various in situ characterization methods, such as in situ infrared spectroscopy, in situ Raman spectroscopy, and in situ electron microscopy, are used to monitor the evolution of the reaction intermediates and catalyst surface structures during the CO₂RR process. The results are used to reveal the regulatory effects of the catalyst surface and electronic structure on the catalytic reaction and its kinetic mechanism. Third, design of the electrode structure through the modification of hydrophobic materials (such as polytetrafluoroethylene) and improvement of the hydrophobic performance of the electrode surface to avoid issues with flooding during long-term operation and improve the electrode stability. The structure of electrolytic reactor is optimized to enhance mass transfer and energy efficiency.

The major countries and institutions in recent years for output of core papers on the engineering research front of “high- performance electrocatalysts and electrolysis systems for CO₂ conversion and utilization” are shown in Tables 1.2.9 and 1.2.10, respectively. Among the major countries producing core papers, China is ranked first, with 71 core papers (66.36% of the total), which is much higher than the numbers produced in the USA, Australia, Canada, and other countries. Among the major institutions producing core papers, Chinese Academy of Sciences is ranked first, followed by University of Science and Technology of China, and Stanford University. The major collaborations among countries and institutions are plotted in Figures 1.2.7 and 1.2.8, respectively. Most of China’s collaborations are with the USA, and it also closely cooperates with Australia, Canada, and Singapore. The top three countries in terms of the number of citing core papers are China, the USA, and Australia (Table 1.2.11). The proportion of citing papers from China is 57.95%, which indicates that Chinese scientists have paid close attention to the research trends in this area. Most of the major institutions producing citing core papers are in China, including Chinese Academy of Sciences, University of Science and Technology of China, and Tianjin University (Table 1.2.12)

It is an important to develop green and low-carbon energy technology to activate and transform CO₂ through electrocatalytic mild conditions to synthesize the chemicals needed for social and economic development. The electrocatalytic conversion of CO₂ is a complex multi-scale process, involving CO₂ molecular adsorption and conversion, nano-scale catalysts, micron-scale membrane electrodes, and macro-scale electrolyzers. Current research is mainly focused on finding and improving high-performance electrocatalysts. Future research should look at combining various in situ characterization methods for electrode morphology

《Table 1.2.9》

Table 1.2.9 Countries with the greatest output of core papers on “high-performance electrocatalysts and electrolysis systems for CO₂ conversion and utilization”

《Table 1.2.10》

Table 1.2.10 Institutions with the greatest output of core papers on “high-performance electrocatalysts and electrolysis systems for CO₂ conversion and utilization”

《Figure 1.2.7》

Figure 1.2.7 Collaboration network among major countries for the engineering research front of “high-performance electrocatalysts and electrolysis systems for CO₂ conversion and utilization”

《Figure 1.2.8》

Figure 1.2.8 Collaboration network among major institutions for the engineering research front of “high-performance electrocatalysts and electrolysis systems for CO₂ conversion and utilization”

evolution, reaction process condition optimization, electrode/electrolyte interface evolution, mass transfer transportation optimization, catalyst stability improvement, and electrolyte/solvent effect. Additionally, for the future industrial application of electrocatalytic reduction of CO₂, the following points need to be considered: determining the practical application objectives, evaluating the economics of chemical products and market supply and demand, expanding the scale of CO₂ electrolyzers, improving the long-term continuous operation stability of electrocatalysts, and calculating the cost of product separation and raw material recovery. The roadmap of the engineering research front of “high-performance electrocatalysts and electrolysis systems for CO₂ conversion and utilization” is shown in Figure 1.2.9.

《Table 1.2.11》

Table 1.2.11 Countries with the greatest output of citing papers on “high-performance electrocatalysts and electrolysis systems for CO₂ conversion and utilization”

《Table 1.2.12》

Table 1.2.12 Institutions with the greatest output of citing papers on “high-performance electrocatalysts and electrolysis systems for CO₂ conversion and utilization”

《Figure 1.2.9》

Figure 1.2.9 Roadmap of the engineering research front of “high-performance electrocatalysts and electrolysis systems for CO₂ conversion and utilization”

《2. Engineering development fronts》

2. Engineering development fronts

《2.1 Trends in Top 11 engineering development fronts》

2.1 Trends in Top 11 engineering development fronts

The Top 11 engineering development fronts as assessed by the Field Group of Chemical, Metallurgical, and Materials Engineering are shown in Table 2.1.1. “Design and preparation of metal matrix composites for high-temperature environments”, “construction and large-scale manufacturing technology of high-efficiency photovoltaic devices”, “low-temperature and low-pressure thermal catalytic ammonia synthesis over a wide loading range”, and “development of ironmaking technology for hydrogen-rich carbon cycle blast furnaces” were recommended by experts directly. The other fronts were chosen by a panel of experts according to core-paper statistics provided by Clarivate. The annual numbers of core patents for all fronts show overall growth, especially for “integration of large language models for the design and synthesis of advanced chemical engineering materials”, “efficient and energy-saving separation technologies for energy intensive chemical processes”, and “development of ironmaking technology for hydrogen-rich carbon cycle blast furnaces” (Table 2.1.2).

(1) Metallurgical low-carbon utilization of renewable energy

The smelting process of complex metal materials requires a large amount of electricity and relies on the reduction characteristics of fossil fuels and combustion heating. This is the key to restrict the low-carbon sustainable development of the metallurgical

《Table 2.1.1》

Table 2.1.1 Top 11 engineering development fronts in chemical, metallurgical, and materials engineering

《Table 2.1.2》

Table 2.1.2 Annual number of core patents published for the Top 11 engineering development fronts in chemical, metallurgical, and materials engineering