Synthesis gas, composed of H₂ and CO, is an important fuel which serves as feedstock for industrially relevant processes, such as methanol or ammonia synthesis. The efficiency of these reactions depends on the H₂: CO ratio, which can be controlled by a careful choice of reactants and catalyst surface chemistry. Here, using a combination of environmental scanning electron microscopy (ESEM) and online mass spectrometry, direct visualization of the surface chemistry of a Ni catalyst during the production of synthesis gas was achieved for the first time. The insertion of a homebuilt quartz tube reactor in the modified ESEM chamber was key to success of the setup. The nature of chemical dynamics was revealed in the form of reversible oxide-metal phase transitions and surface transformations which occurred on the performing catalyst. The oxide-metal phase transitions were found to control the production of synthesis gas in the temperature regime between 700 and 900 °C in an atmosphere relevant for dry reforming of methane (DRM, CO₂: CH₄ =0.75). This was confirmed using high resolution transmission electron microscopy imaging, electron energy loss spectroscopy, thermal analysis, and C¹⁸O₂ labelled experiments. Our dedicated operando approach of simultaneously studying the surface processes of a catalyst and its activity allowed to uncover how phase transitions can steer catalytic reactions.

由H ₂和CO组成的合成气是一种重要的燃料，可用作工业相关过程（例如甲醇或氨合成）的原料。这些反应的效率取决于H ₂：CO比，可以通过仔细选择反应物和催化剂表面化学来控制。在此，结合使用环境扫描电子显微镜（ESEM）和在线质谱分析技术，首次实现了在合成气生产过程中直接观察镍催化剂的表面化学性质。在改良的ESEM室中插入一个自制的石英管反应器是成功安装的关键。化学动力学的性质以在可运行的催化剂上发生的可逆的氧化物-金属相变和表面转变的形式揭示。发现氧化物-金属相变可在与甲烷干重整相关的气氛（DRM，CO ₂：CH ₄＝ 0.75）。使用高分辨率透射电子显微镜成像，电子能量损失谱，热分析和C ¹⁸ O ₂标记的实验证实了这一点。我们专用的操作方法同时研究催化剂的表面过程及其活性，从而揭示了相变如何引导催化反应。