(570b) Process Intensified Modular Production of Clean Hydrogen and Carbon Nanomaterials from Natural Gas By Microwave Catalytic Pyrolysis

Microwave catalytic pyrolysis is a feasible pathway for decarbonization natural gas, producing clean hydrogen and valuable carbon nanomaterials without emitting CO₂. More importantly, the process can be portable, modular, and electrification oriented. In this work, we have developed novel and advanced catalysts for attenuating microwave energy, such as multiwalled carbon nanotube supported Ni-based bimetallic nanoparticles (Ni-Pd, Ni-Cu and Ni-Fe), Zr oxides supported Co, exsolved Ni nanoparticles from perovskites matrix (ABTiNiO). Microwave could provide site-specific selective heating with catalyst support temperature being relatively low while the active site temperature being sufficiently high for the methane decomposition reaction. Our data indicated microwave heating helped reduce the activation energy needed for this reaction as well. For example, CNT supported Ni-Cu catalyst can reduce the activation energy of the reaction from 45.5 kJ/mol CH₄ under conventional electrical heating to 24.8 kJ/mol CH₄ under microwave, which was measured with a reaction temperature range from 450 to 600 °C. It was found that the small amount of metal promoter like Cu in the Ni-Cu-CNT catalyst system could modify the carbon nanoproducts from bamboo-shaped CNTs to multiwalled CNTs. In addition, we found that Fe could eventually become a more affordable promoter choice in the CNT support Ni-based catalysts after measurements of activation energies from Ni-Pd, Ni-Cu, and Ni-Fe options. We have also conducted a process simulation and techno-economic analysis of our microwave process that showed the minimum hydrogen selling price was about $1/kg H₂, which made our process very promising to achieve the goal of Department of Energy to reduce hydrogen production cost to $1/kg in a decade. In addition, methane plasma pyrolysis product, acetylene, was evaluated with the same CNT supported Ni-based catalyst and showed nearly 100% conversion to hydrogen and carbon nanotubes. Other catalysts such as Zr oxides supported Co and exsolved Ni nanoparticles typically had decent methane conversion rates, but they needed microwave absorbing materials, which were inert to the methane decomposition reactions, as assistance for heating purpose only. Perovskites based Ni catalysts such as SrTiNiO and BaTiNiO had decent conversion of methane and microwave absorbance while the deactivation was faster than those CNTs support Ni-based metal nanoparticles. The work has further successfully separated the metal from CNT product with an acid-wash method. The recovered metal can be used to generated new catalyst. Methane can be converted to acetylene under microwave plasma condition. In a single microwave plasma reactor, acetylene can be converted in the post-plasma zone. The results showed that CNT supported Ni-based and inexpensive alternative Al₂O₃ supported Ni nanoparticles could be a great downstream catalyst for stable conversion of methane derived acetylene to hydrogen and carbon nanotubes. To summarize, the work has developed microwave-suitable catalysts to achieve natural gas catalytic pyrolysis to simultaneously produce valuable carbon nanomaterials and clean hydrogen, which has also been confirmed success in a scaled-up reactor. Our technology possesses a great potential in transforming natural gas to value-added products.