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.
Highlights
Global warming remains one of the greatest challenges
The coke-resistant property of the NiCo catalyst was investigated via experiments and density functional theory based calculation
Between an adsorbed coke species to the Ni active site, in which in the case of pure Ni catalyst, it is observed to be very strong. Another role of Co is to facilitate the coke movement on the catalyst surface, reducing the chance of coke deposition on Ni active site comparing to the pure Ni and Co surfaces during the dry reforming of methane (DRM) process
Summary
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. Tu et al.[30] provided an extensive experimental and computational investigation on an improved DRM activity and stability of NiCo due to reactive oxygen species on metal active sites They found that the presence of reactive oxygen species promotes carbonaceous intermediates (CHx*) removal during DRM resulting in high availability of the active sites for C–H bond activation. We applied experimental characterizations and reaction testing combined with the DFT analysis to investigate the insight effect of NiCo catalyst surface in terms of coke behavior and coke resistance. The coke mobility during the 3-stage diffusion is modeled on a real NiCo particle as a function of Ni-dominant, Co-dominant, and NiCo-dominant regions described by the ternary contour plot of coke diffusion rate on the surface
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