Tailoring Plasma-Catalysis to Rethink Surface Inactivation and Product Speciation in Direct Methane Conversion

In this talk, we show how catalysts and plasmas can be designed synergistically to break catalytic scaling laws, tune product speciation (i.e., form ethane, ethene, etc.), and limit coking of catalytic surfaces. We use model experiments and a microkinetic model to show that low temperature plasma-catalysis breaks catalytic scaling laws by lowering the activation barrier of CH₄ dissociative adsorption and shifts the optimal catalyst to more noble surfaces. We demonstrate a packed bed dielectric barrier discharge (DBD) achieves emission free CH₄ conversion at near room temperature (473 K) producing 45 times more hydrogen (H₂) on 20% Ni/Al₂O₃ than gas-phase plasma alone. We show independent control of vibrational (T_vib) and surface temperature (T_surface) allows selective formation of upgraded C₂ hydrocarbons. Ethene (C₂H₄) and ethane (C₂H₆) are the primary upgraded C₂ hydrocarbons on 20% Pt/Al₂O₃ and 20% Cu/Al₂O₃ at T_surface = 473 K and T_vib = 4200 K, respectively. We show that tuning catalysts and plasma excitation also limits coking and the inactivation of catalysts. Experiments show that while 20% Ni/Al₂O₃ produces more H₂ initially, it deactivates rapidly due to coking. Conversely, 20% Cu/Al₂O₃ maintains stable H₂ and C₂H₆ production for over 15 hours. Simulations reflect this deactivation behavior, and ex-situ surface analysis through SEM/EDS, XPS, and TEM/EDX confirm the correlation between simulated and observed forms of carbon coverage on the catalyst. This work illustrates co-designing catalysts and plasma to promote desirable reaction pathways.