Chen Xiaobo, Wang Jianyu, Patel Shyam Bharatkumar, Ye Shuonan, Wu Yupeng, Zhou Zhikang, Qiao Linna, Wang Yuxi, Marinkovic Nebojsa, Li Meng, Hwang Sooyeon, Zakharov Dmitri N, Ma Lu, Wu Qin, Boscoboinik Jorge Anibal, Yang Judith C, Zhou Guangwen
Department of Mechanical Engineering & Materials Science and Engineering Program, State University of New York at Binghamton, Binghamton, NY, USA.
Materials Science and Chemical Engineering Department, Stony Brook University, Stony Brook, NY, USA.
Nature. 2025 Aug;644(8078):927-932. doi: 10.1038/s41586-025-09394-0. Epub 2025 Aug 20.
Understanding oxide reduction is critical for advancing metal production, catalysis and energy technologies. Although carbon monoxide (CO) and hydrogen (H) are widely used reductants, the mechanisms by which they work are often presumed to be similar, both involving lattice oxygen removal. However, because of growing interest in replacing CO with H to lower CO emissions, distinguishing gas-specific reduction pathways is critical. Yet, capturing these atomic-scale processes under reactive gas and high-temperature conditions remains challenging. Here we use environmental transmission electron microscopy, which is capable of real-time, atomic-resolution imaging of gas-solid redox reactions, to directly visualize the gas-dependent oxide reduction dynamics in NiO. We show that CO drives surface nucleation and the growth of metallic Ni islands, leading to self-limiting surface metallization. Conversely, H activates a coupled surface-to-bulk transformation, where protons from dissociated H infiltrate the oxide lattice to promote the inward migration of surface-generated oxygen vacancies and enabling bulk metallization. By contrast, oxygen vacancies formed by CO remain confined near the surface, where they rapidly form a metallic Ni layer that inhibits further reduction. These results reveal distinct atomistic pathways for CO and H and provide insights that may guide metallurgical processes and catalyst design.
理解氧化物还原对于推进金属生产、催化和能源技术至关重要。尽管一氧化碳（CO）和氢气（H）是广泛使用的还原剂，但它们的作用机制通常被认为是相似的，都涉及晶格氧的去除。然而，由于越来越关注用H替代CO以降低CO排放，区分特定气体的还原途径至关重要。然而，在反应性气体和高温条件下捕捉这些原子尺度的过程仍然具有挑战性。在这里，我们使用环境透射电子显微镜，它能够对气-固氧化还原反应进行实时、原子分辨率成像，以直接观察NiO中依赖气体的氧化物还原动力学。我们表明，CO驱动表面成核和金属Ni岛的生长，导致自限性表面金属化。相反，H激活了一种从表面到体相的耦合转变，其中解离的H产生的质子渗透到氧化物晶格中，促进表面产生的氧空位向内迁移并实现体相金属化。相比之下，由CO形成的氧空位仍局限在表面附近，在那里它们迅速形成一层金属Ni层，抑制进一步还原。这些结果揭示了CO和H不同的原子途径，并提供了可能指导冶金过程和催化剂设计的见解。
