Datensatz

Zusammenfassung

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.