Methane steam reforming is an important industrial
process for hydrogen production, employing Ni as a low-cost, highly
active catalyst, which, however, suffers from coking due to methane
cracking. Coking is the accumulation of a stable poison over time,
occurring at high temperatures; thus, to a first approximation, it can be
treated as a thermodynamic problem. In this work, we developed an Ab
initio kinetic Monte Carlo (KMC) model for methane cracking on
Ni(111) at steam reforming conditions. The model captures C−H
activation kinetics in detail, while graphene sheet formation is described
at the level of thermodynamics, to obtain insights into the “terminal
(poisoned) state” of graphene/coke within reasonable computational
times. We used cluster expansions (CEs) of progressively higher fidelity to systematically assess the influence of effective cluster
interactions between adsorbed or covalently bonded C and CH species on the “terminal state” morphology. Moreover, we compared
the predictions of KMC models incorporating these CEs into mean-field microkinetic models in a consistent manner. The models
show that the “terminal state” changes significantly with the level of fidelity of the CEs. Furthermore, high-fidelity simulations predict
C−CH island/rings that are largely disconnected at low temperatures but completely encapsulate the Ni(111) surface at high
temperatures
