Experimental and computational investigation on underlying factors promoting high coke resistance in NiCo bimetallic catalysts during dry reforming of methane

Abstract

Global warming remains one of the greatest challenges. One of the most prominent solutions is to close the carbon cycle by utilizing the greenhouse gas: CO2, and CH4, as a feedstock via the dry reforming of methane (DRM). This work provided an insight into how the NiCo bimetallic catalyst can perform with high stability against coking during DRM compared to the Ni and Co monometallic catalysts, in which the experimental and computational techniques based on density functional theory were performed. It was found that the high stability against coking found on the NiCo surface can be summarized into two key factors: (1) the role of Co weakening the bond between a Ni active site and coke (2) significantly high surface coke diffusion rate on NiCo. Moreover, the calculation of the surface fraction weighted rate of coke diffusion which modeled the real NiCo particle into four regions: Ni-dominant, Co-dominant, NiCo-dominant, and the mixed region consisting a comparable amount of the former there regions, have shown that the synthesis of a NiCo particle should be dominated with NiCo region while keeping the Ni-dominant, and Co-dominant regions to be as low as possible to facilitate coke diffusion and removal. Thus, to effectively utilize the coke-resistant property of NiCo catalyst for DRM, one should together combine its high coke diffusion rate with coke removal mechanisms such as oxidation or hydrogenation, especially at the final diffusion site, to ensure that there will not be enough coke at the final site that will cause back-diffusion.

Influence of the Cobalt Active Site Neighbours in NiCo Nanocatalysts for Phosphine‐Assisted Silane Activation

“…[6][7][8] Combinations of transition metals (Fe, Co, Ni, Cu) sometime present a catalytic activity competitive with these of scarce and expensive platinoid catalysts, which stimulated their investigations. In particular, variously shaped nickel-cobalt nanoparticles were applied as catalysts for many reactions such as methane dry reforming, [9][10][11][12][13] hydrogenations, [14][15][16][17][18] lignin depolymerization, [19] water splitting [20] and aldehyde hydrosilylation. [21] For example, while nickel alone is highly active for methane dry reforming, it rapidly deactivates because of coke formation.…”

“…Moreover, coke diffusion was accelerated on the NiCo alloy, reducing the poisoning of Ni active site. The alloying leads to electronic effects which decrease the bonding strength between Nickel and coke [13] …”

“…The alloying leads to electronic effects which decrease the bonding strength between Nickel and coke. [13] Molecular additives also have a huge impact on the catalytic behaviour of metallic nanoparticles, might they be native ligands for colloidal nanoparticles, [22] substrates of the catalytic reaction [23] or added Lewis acid or bases. [21] For example, Guo et al evidenced both experimentally and computationally the hydrogenation ability of gold nanoparticles in presence of small imines.…”

Role of support bio-templating in Ni/Al2O3 catalysts for hydrogen production via dry reforming of methane

“…Though, the problems associated with these metals are their high cost, unavailability, and low stability in high reaction temperatures of DRM 26 , 27 . In contrast, the supported transition metals, especially Ni, have been extensively used as a potential alternative because of their high initial activity and relatively low cost 27 – 31 . However, the catalyst deactivation hindered the Ni-based DRM commercialization.…”

Dry reforming of methane over Ni/KCC-1 catalyst for syngas production

“…Renewable energy may serve as alternatives to fossil fuels that alleviate this challenge, such as hydropower, wind and solar power, but these sources depend on geographical, nocturnal and seasonal variations. In green energy science, reducing greenhouse gas emissions has become one of the most important challenges in minimizing temperature increases and coping with global warming [9], [10]. The conversion of two greenhouse gases, methane and carbon dioxide, into a value-added product called synthetic gas, can be accomplished by methane steam reforming (SRM), methane partial oxidation (POM) and methane dry reforming (DRM).…”