Coking Can Enhance Product Yields in the Dry Reforming of Methane

Influence of NiO into the CO2 capture of Li4SiO4 and its catalytic performance on dry reforming of methane

Carbon capture, utilization, and storage (CCUS) technology offer promising solution to mitigate the threatening consequences of large-scale anthropogenic greenhouse gas emissions. Within this context, this report investigates the influence of NiO deposition on the Li4SiO4 surface during the CO2 capture process and its catalytic behavior in hydrogen production via dry methane reforming. Results demonstrate that the NiO impregnation method modifies microstructural features of Li4SiO4, which positively impact the CO2 capture properties of the material. In particular, the NiO-Li4SiO4 sample captured twice as much CO2 as the pristine Li4SiO4 material, 6.8 and 3.4 mmol of CO2 per gram of ceramic at 675 and 650 °C, respectively. Additionally, the catalytic results reveal that NiO-Li4SiO4 yields a substantial hydrogen production (up to 55 %) when tested in the dry methane reforming reaction. Importantly, this conversion remains stable after 2.5 h of reaction and is selective for hydrogen production. This study highlights the potential of Li4SiO4 both a support and a captor for a sorption-enhanced dry reforming of methane. To the best of our knowledge, this is the first report showcasing the effectiveness of Li4SiO4 as an active support for Ni-based catalysis in the dry reforming of methane. These findings provide valuable insights into the development of this composite as a dual-functional material for carbon dioxide capture and conversion.

Highly Efficient and Stable Methane Dry Reforming Enabled by a Single-Site Cationic Ni Catalyst

Zeolite-supported nickel (Ni) catalysts have been extensively studied for the dry reforming of methane (DRM). It is generally believed that prior to or during the reaction, Ni is reduced to a metallic state to act as the catalytic site. Here, we employed a ligand-protected synthesis method to achieve a high degree of Ni incorporation into the framework of the MFI zeolite. The incorporated Ni species retained their cationic nature during the DRM reaction carried out at 600 °C, exhibiting higher apparent catalytic activity and significantly greater catalytic stability in comparison to supported metallic Ni particles at the same loading. From theoretical and experimental evidence, we conclude that the incorporation of Ni into the zeolite framework leads to the formation of metal-oxygen (Niδ+-O(2-ξ)-) pairs, which serve as catalytic active sites, promoting the dissociation of C-H bonds in CH4 through a mechanism distinct from that of metallic Ni. The conversion of CH4 on cationic Ni single sites follows the CHx oxidation pathway, which is characterized by the rapid transformation of partial cracking intermediates CHx*, effectively inhibiting coke formation. The presence of the CHx oxidation pathway was experimentally validated by identifying the reaction intermediates. These new mechanistic insights elucidate the exceptional performance of the developed Ni-MFI catalyst and offer guidance for designing more efficient and stable Ni-based DRM catalysts.

Ni nanoparticles supported on Al2O3 + La2O3 yolk-shell catalyst for photo-assisted thermal decomposition of methane

Catalytic methane decomposition (CMD) has emerged as an appealing technology for large-scale production of H₂ and carbon nanostructures from natural gas. As the CMD process is mildly endothermic, the application of concentrated renewable energy sources such as solar energy under a low-temperature regime could potentially represent a promising approach towards CMD process operation. Herein, Ni/Al₂O₃-La₂O₃ yolk-shell catalysts are fabricated using a straightforward single-step hydrothermal approach and tested for their performance in photothermal CMD. We show that the morphology of the resulting materials, dispersion and reducibility of Ni nanoparticles, and nature of metal-support interactions can be tuned by addition of varying amounts of La. Notably, the addition of an optimal amount of La (Ni/Al-20La) improved the H₂ yield and catalyst stability relative to the base Ni/Al₂O₃ material, while also favoring base growth of carbon nanofibers. Additionally, we show for the first time a photothermal effect in CMD, whereby the introduction of 3 suns light irradiation at a constant bulk temperature of 500 °C reversibly increased the H₂ yield of catalyst by about 1.2 times relative to the rate in the dark, accompanied by a decrease in apparent activation energy from 41.6 kJ mol^-1 to 32.5 kJ mol^-1. The light irradiation further suppressed undesirable CO co-production at low temperatures. Our work reveals photothermal catalysis as a promising route for CMD while providing an insightful understanding of the roles of modifier in enriching methane activation sites on Al₂O₃-based catalysts.

Promoted coke resistance of Ni by surface carbon for the dry reforming of methane

Dry reforming of methane (DRM) is an efficient process to transform methane and carbon dioxide to syngas. Nickel could show good catalytic activity for DRM, whereas the deactivation of nickel surfaces by the formation of inert carbon structures is inevitable. In this study, we carry out a detailed investigation of the evolution and catalytic performance of the carbon-covered surface structure on Ni(100) with a combined density functional theory and microkinetic modeling approach. The results suggest that the pristine Ni(100) surface is prone to carbon deposition and accumulation under reaction conditions. Further studies show that over this carbon-covered reconstructed Ni(100) surface, a carbon-based Mars-van-Krevelen mechanism would be favored, and the activity and coke resistance is promoted. This surface state and reaction mechanism were rarely reported before and would provide more insights into the DRM process under real reaction conditions and would help design more stable Ni catalysts.