Are Carbon-Based Materials Good Supports for the Catalytic Reforming of Ammonia?

Abstract

Carbon-based materials are commonly used in catalysis as metal-free catalysts and as supports for metal particles. We investigated a series of graphene point defects using the density functional theory (DFT) and shed light on their role in the catalytic reforming of ammonia. The adsorption of molecules and reaction intermediates on carbon vacancies, lattice reconstruction, partial oxidation, and dopants was analyzed to provide details on the most favorable interactions. Thermochemical investigations revealed the structures active for NH3 adsorption and dehydrogenation. Based on transition-state theory, we implemented microkinetic simulations and found that the rate-determining step is either NH3 activation or the desorption of reformed molecules, depending on the defect type. However, investigated defects are ineffective to desorb the reaction products, i.e., N2 and H2. Batch reaction simulations within wide temperature and time ranges indicated that although NH3 dehydrogenation may occur, the active sites become poisoned by the H or N anchored atoms; therefore, in the long term, carbon-based materials are inert toward NH3 reforming.