(702b) Density Functional Theory Study of Dry Reforming of Methane on Pure Nickel As Well As Transition Metal Overlayer Deposited Nickel Surfaces

Dry reforming of methane (DRM) reaction utilizes CO₂, a major greenhouse gas to convert natural gas (mainly composed of methane) to synthesis gas, an important feedstock which could further be converted into valuable chemicals and cleaner fuel. This reaction presents a clear incentive in terms of its positive impact on the global environment and thus it has gained increasing attention from the scientific community lately. The superior catalytic activity of Nickel based catalysts and also their relatively lower costs make them the most promising catalyst for this reaction. However, these catalysts also deactivate rapidly owing to their high susceptibility to coke formation and filamentous carbon deposition. This severe catalyst deactivation is one of the major drawbacks that is obstructing the widespread commercialization of DRM. Several alternative catalysts have been explored for this reaction, including noble metals such as Rh and Ru. Even though these metals are found to be more reactive, as well as more resistant to carbon deposition, their high cost generally hinders their use [1]. One of the techniques that has been proposed to suppress the coke formation on the nickel surface is the substitution of single foreign transition metal atom which could modify the electronic structure [2].

In the current work, we present our exhaustive work on the solid state density functional theory (DFT) model results to study theoretically the wide network of elementary reactions comprising the DRM reaction on various facets of pure nickel catalyst, such as Ni(111), Ni(100) and Ni(110) surfaces. Calculations were performed using rev-PBE as exchange-correlation functional within the generalized gradient approximation (GGA) as implemented in the software VASP. Long term interactions such as the van der Waals forces are quite critical for the accurate description of the adsorption energies. Thus the DFT-D3 method of Grimme is used to account for dispersion corrections. Adsorption energies were calculated for all the DRM reaction intermediate species and then subsequently the activation barriers were calculated for all the elementary reactions in the DRM cycle. The catalytic activity of these pure nickel surfaces in terms of DRM reaction rate are then compared to the rates obtained on the single overlayer deposited nickel (X/Ni) surfaces where X is a transition metal such as Cu, Rh and Pd. Electronic structure analysis of various pure as well as overlayer modified surfaces is performed in terms of the d-band theory of catalysis. Our results indicate that the catalyst stability is greatly improved by a transition metal overlayer deposition on nickel surface.

References:

1. Pakhare, D. and J. Spivey, A review of dry (CO2) reforming of methane over noble metal catalysts. Chemical Society Reviews, 2014. 43(22): p. 7813-7837

2. Fan, C.; Zhu, Y.; Xu, Y.; Zhou, Y.; Zhou, X. and Chen, D; Origin of synergistic effect over Ni-based bimetallic surfaces: A density functional theory study. The Journal of Chemical Physics, 2012. 137: 014703