Kinetic Study of Non-Thermal Plasma (NTP) Activated Catalytic CO2 Hydrogenation over Ni Supported on Silica-Catalyst

Non-thermal plasma (NTP) is a promising alternative to the conventional thermal activation for promoting efficient heterogeneous catalysis under ambient conditions. However, the full understanding of the hybrid NTP-catalyst system is challenging due to its complexity. Herein, using the catalytic CO2 hydrogenation over the Ni@SiO2 catalyst as the model system, we carried out comparative kinetic studies of the catalysis under both thermal and NTP conditions to assess the reaction dynamics and kinetics, aimed at understanding the interactions between NTP and catalyst surface. Specifically, process parameters performance was evaluated by varying temperature, total flow rate, partial pressure of H2 and dielectric barrier discharge (DBD) discharge power. Kinetic studies showed that, under the NTP conditions, the catalysis exhibited non-Arrhenius behaviour likely due to the complex interactions between NTP and Ni catalyst, showing a linear correlation between the natural logarithmic TOF and the reciprocal DBD discharge power (instead of the bulk reactor temperature measured). Additionally, under the conditions used, the activation energy of the catalysis under the NTP conditions was independent from the total feed flow rate (at ~29 kJ mol−1, being significantly lower than that of the thermal catalysis (i.e., ~80 kJ mol−1). Kinetic studies suggested that the dissociated H species due to NTP discharge in the gas phase are ready to interact with Ni surfaces, and thus reducing the activation barrier required to enable the surface reactions.