Coking is the primary cause of the deactivation of nickel-based catalysts during dry reforming of methane (DRM). One of the key steps toward coke formation is the diffusion of carbon across the bulk of catalysts. Doping platinum onto nickel surfaces hinders such diffusion, but it may also reduce the activity of catalysts. Being the first step towards theoretical optimization of Pt concentration, in this work, we investigated the correlation between the reaction energy of atomic carbon diffusion from surface to subsurface (ΔEdiff) and the surface distribution of Pt on NiPt(111) using DFT. Both the substitution of the nearest-neighbor Ni atoms (denoted as Ni1) of C atom and the substitution of the second nearest Ni (denoted as Ni2) with Pt were discussed. In both scenarios, ΔEdiff is found linearly correlated to the number of Pt. However, the diffusion is found more endothermic by replacing Ni1, while that becomes more exothermic by substituting Ni2. To explain this opposite trend, we investigated the binding energy (ΔEbind) of both surface C and subsurface C. We find that doping Pt always decreases ΔEbind of C, but the steepness of such a decrease varies by the location of both Pt and C. On one hand, substituting Ni1 reduces ΔEbind of subsurface C the most among all ΔEbind of C, 0.30 eV per Pt atom, while that reduces ΔEbind by 0.20 eV per Pt atom for surface-adsorbed C. The less steep decrease of ΔEbind for surface C therefore results in less negative ΔEdiff by replacing Ni1. On the other hand, substituting one Ni2 atom with Pt only destabilizes the binding of surface C with 0.08 eV and shows no effect on the binding of subsurface C. It thus results in more negative ΔEdiff. These trends indicate that the effect of Pt atom on C binding decays significantly with distance. Such an observation theoretically supports the development of a descriptor to predict ΔEdiff based only on the location and the intrinsic properties of metal atoms near C. Such a descriptor is under development. We believe that the proposed descriptor will thus pave the way towards the efficient first-principles-based multiscale modeling of coke formation during DRM, which is essential in the theoretical optimization of Pt concentration of NiPt alloy.

First-principles investigation of determining topological factors in anti-coking performance of NiPt bimetallic alloys

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