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

非技术摘要钢是最重要的工业材料之一，年产量超过20亿吨。然而，它的生产是以环境为代价的。炼钢占所有人为温室气体排放量的7-11%。面对来自政府和投资者的减排压力，钢铁行业正在尝试绿色钢铁项目，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，在绿色钢技术能够进步之前，需要对利用氢气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。该项目使用高度先进的技术来了解氢基直接还原，通过在原子水平上沿着沿着不同的时间点获得前所未有的化学反应观察。该项目将这些原子解析的实验与紧密集成的反馈回路中的计算相结合，以实现空间和时间上变化的新的实时观测。作为该研究计划的一部分，研究生和本科生正在学习和使用新的显微镜，光谱学，动力学测量和建模技术，以解决当前能源和环境研究前沿的材料问题。该项目的成果也被纳入本科生和研究生课程以及高中外联方案。 技术摘要虽然氧化物还原在许多重要的工艺过程中起着至关重要的作用，但现有知识的很大一部分是基于中尺度的工作，这些工作太粗糙而不能反映潜在的微观细节。这个项目通过阐明氧化物还原途径的分层相互作用的原子机制来解决这一知识缺口。通过采用原位实验和协调的理论模型的独特组合，该项目阐明了i）导致氧化物还原开始的H2吸附的元素步骤; ii）通过多界面转变控制氧化物还原传播和微观结构演变的微观机制;和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必要的见解，反应活性位点，瞬态，传质机制，反应活化能和反应途径。该研究确定了控制效率，动力学和金属收率的关键结构和化学参数，这将导致更有效的氢基直接还原方法，对钢铁行业迫切需要的脱碳具有潜在的高度影响。实验和理论工作的总和也提供了基础知识，用于构建氧化物还原的预测和分层多尺度模型，这些模型自然地将不同的反应阶段联系起来，将原子过程与宏观行为联系起来，并打开了通过控制底层原子过程来定制气固反应的大门。这些基本的见解为腐蚀、电化学和催化等其他领域带来了光明，这些领域也出现了基本过程的原型。该奖项反映了NSF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.