Atomistic mechanisms and dynamics of hydrogen-based reduction of iron ores

钢铁是最重要的工业材料之一，年产量超过20亿吨。然而，它的生产为环境付出了高昂的代价。炼钢占所有人为温室气体排放的7-11%。面对来自政府和投资者不断升级的减排压力，钢铁行业正在试验绿色钢铁项目，通过使用氢气代替传统的碳密集型制造来减少温室气体排放。然而，在绿色钢铁技术取得进展之前，需要对利用氢将氧化铁转化为铁的化学过程有基本的了解。这个过程被称为氢基直接还原。该项目采用高度先进的技术，通过获取从未见过的化学反应在原子水平上沿着不同的时间点的观察，来了解氢基直接还原。该项目将这些原子分解实验与紧密集成的反馈回路中的计算相结合，以实现空间和时间变化的新的实时观测。作为该研究计划的一部分，研究生和本科生将学习并使用新的显微镜、光谱学、动力学测量和建模技术来研究当前能源和环境研究前沿的材料问题。这个项目的成果也被纳入了本科和研究生课程以及高中的推广项目。虽然氧化物还原在许多技术上重要的过程中起着至关重要的作用，但目前的很大一部分知识是基于中尺度的工作，这些工作太粗糙，无法反映潜在的微观细节。该项目通过阐明氧化还原途径层次相互作用的原子机制来解决这一知识差距。通过采用原位实验和协调理论建模的独特组合，该项目阐明了i) H2吸附导致氧化物还原开始的基本步骤；Ii)通过多界面转变控制氧化还原扩展和微观结构演化的微观机制；iii)由于H2和气态产物H2O的对抗作用，导致可逆氧化还原循环的原子过程。清楚地解决这些问题提供了对反应活性位点、瞬态、质量传递机制、反应活化能和反应途径的基本见解。该研究确定了控制效率、动力学和金属产量的关键结构和化学参数，这些参数将导致更有效的基于h2的直接还原方法，对钢铁行业迫切需要的脱碳产生潜在的重大影响。实验和理论努力的总和也为构建氧化物还原的预测和分层多尺度模型提供了基础知识，这些模型自然地将不同的反应阶段联系起来，将原子过程与宏观尺度行为联系起来，并通过控制潜在的原子过程来调整气固反应。这些基本的见解正在为腐蚀、电化学和催化等其他领域带来光明，在这些领域，基本过程的原型也会出现。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL ABSTRACTSteel is one of the most important industrial materials, with more than 2 billon tons produced annually. Its production, however, comes at a steep price for the environment. Steelmaking accounts for 7-11% of all human-made greenhouse gas emissions. Facing escalating pressure from governments and investors to reduce emissions, the steel industry is experimenting with green steel projects that reduce greenhouse emissions by using hydrogen instead of traditional carbon-intensive manufacturing. However, fundamental understanding of the chemical processes that transform Iron oxide into Iron by use of hydrogen is required before green steel technology can advance. This process is called hydrogen-based direct reduction. This project uses highly advanced techniques to understand hydrogen-based direct reduction by acquiring never before seen observations of the chemical reaction at the level of atoms along various points throughout time. This project combines these atomistically resolved experiments with computation in tightly integrated feedback loops, to achieve new real-time observations which vary both spatially and temporally. As part of this research program, students at the graduate and undergraduate levels are learning and using new microscopy, spectroscopy, kinetic measurement and modeling techniques to work on materials issues that are at the forefront of current energy and environmental research. Results from this project are also being incorporated into undergraduate and graduate courses as well as high school outreach programs. TECHNICAL ABSTRACT Although oxide reduction plays a crucial role in many technologically important processes, a significant portion of current knowledge is based upon work at the mesoscale that is too coarse to reflect underlying microscopic details. This project addresses this knowledge gap by elucidating the atomistic mechanisms underlying the hierarchical interplay of oxide reduction pathways. By employing a unique combination of in situ experiments and coordinated theoretical modeling, this project elucidates i) the elemental steps of H2 adsorption leading to the onset of oxide reduction; ii) microscopic mechanisms governing the propagation of oxide reduction and microstructure evolution via multi-interfacial transformations; and iii) atomistic processes leading to reversible oxidation-reduction cycles due to the countering action of H2 and gaseous product H2O. Clearly addressing these questions provide essential insights into reaction active sites, transient states, mass transport mechanisms, reaction activation energies and reaction pathways. The study identifies critical structural and chemical parameters for controlling the efficiency, kinetics and metallic yield, which are leading to more efficient H2-based direct reduction methods, with potentially high impact on the urgently needed decarbonization of the steel industry. The sum of experimental and theoretical efforts also provide fundamental knowledge for construction of predictive and hierarchical multi-scale models of oxide reduction that naturally link different reaction stages, relate the atomistic processes with the macroscale behavior, and open the door to tailoring gas-solid reactions via controlling underlying atomic processes. Such fundamental insights are shedding light on other fields such as corrosion, electrochemistry and catalysis, where the prototypes of basic processes also occur.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.