CO Poisoning of Ru Catalysts in CO2 Hydrogenation under Thermal and Plasma Conditions: A Combined Kinetic and Diffuse Reflectance Infrared Fourier Transform Spectroscopy-Mass Spectrometry Study

Plasma-catalysis systems are complex and require further understanding to advance the technology. Herein, CO poisoning in CO2 hydrogenation over supported ruthenium (Ru) catalysts in a nonthermal plasma (NTP)-catalysis system was investigated by a combined kinetic and diffuse reflectance infrared Fourier transform spectroscopy-mass spectrometry (DRIFTS-MS) study and compared with the thermal catalytic system. The relevant findings suggest the coexistence of the Langmuir-Hinshelwood and Eley-Rideal mechanisms in the NTP-catalysis. Importantly, comparative study of CO poisoning of the Ru catalyst was performed under the thermal and NTP conditions, showing the advantage of the hybrid NTP-catalysis system over the thermal counterpart to mitigate CO poisoning of the catalyst. Specifically, compared with the CO poisoning in thermal catalysis due to strong CO adsorption and associated metal sintering, in situ DRIFTS-MS analysis revealed that the collisions of reactive plasma-derived species in NTP-catalysis could remove the strongly adsorbed carbon species to recover the active sites for CO2 activation. Thus, the NTP-catalysis was capable of preventing CO poisoning of the Ru catalyst in CO2 hydrogenation. Additionally, under the NTP conditions, the NTP-enabled water-gas shift reaction of CO with H2O (which was produced by CO/CO2 hydrogenation) shifted the equilibrium of CO2 hydrogenation toward CH4 production.