Carbon nanotubes, as carbon allotropes distinguished by their intricate structures and exceptional physicochemical properties, have demonstrated substantial progress in recent years across diverse domains, including energy production, chemical synthesis, and environmental preservation. They exhibit notable attributes such as high thermal stability, superior adsorption capacity, and a substantial specific surface area, rendering them superb catalyst supports. Particularly in electrochemical energy storage, CNTs are extensively employed in supercapacitor electrodes owing to their elevated electrical conductivity, mechanical robustness, and electrocatalytic prowess, which facilitate significant energy storage capabilities. Their intricate pore architecture and reactive sites make functionalized carbon nanotubes well suited for synthesizing composite materials with diverse components, which are ideal for sequestering carbon dioxide from both atmospheric and indoor environments. This review presents a comprehensive examination of carbon nanotube synthesis methodologies, encompassing chemical vapor deposition, arc discharge, and laser ablation, and evaluates their impacts on the structural and functional properties of carbon nanotubes. Furthermore, this article underscores the applications of carbon nanotubes in fields such as fuel cells, photocatalysis, ammonia synthesis, dry methane reforming, Fischer–Tropsch synthesis, and supercapacitors. Despite the considerable potential of carbon nanotubes, their manufacturing processes remain intricate and costly, impeding large-scale industrial production. This review concludes by addressing the challenges in fabricating carbon nanotube composites and outlining future development prospects.

In recent years, the greenhouse effect has emerged as a major environmental concern. As a result, the utilization and capture of greenhouse gases have become urgent tasks. The dry reforming of methane (DRM) reaction is a technology that directly converts greenhouse gases (CH₄ and CO₂) into valuable products. Ni-based catalysts have gained significant attention and industrial prospects in DRM reactions due to their excellent performance and cost-effectiveness compared to noble metals. However, challenges such as metal sintering and carbon deposition hinder its industrialization. This paper provides a review of the recent advancements in catalyst design for DRM reactions, with a focus on the impact of additives, supports, and preparation methods on Ni-based catalysts. It also describes the reaction and deactivation mechanisms, as well as the thermodynamics and kinetics of DRM reactions. Furthermore, this paper envisions the main challenges and opportunities associated with Ni-based catalysts in DRM research.

The impacts of FeS catalysts on the hydromodification and structural evolution of lignite were investigated using Fourier transform infrared spectroscopy, nuclear magnetic resonance, and X-ray photoelectron spectroscopy. The results indicate that the caking property of lignite can be significantly improved in the presence of the FeS catalyst. When 6.0 wt % FeS was added, the maximum caking index (G_RI) of modified coal reached 95. During the hydromodification, FeS has little effect on the intrinsic water gas shift reaction, but it can increase the CO conversion by promoting the decomposition and hydrogenation of coal so that more active hydrogen is generated and introduced into modified coal. FeS is conducive to the rupture of distal aliphatic groups in the extractible solutes, which promotes the entrance of hydrogen into the aromatic nucleus (H_ar) and α positions (H_α) of asphaltenes and β positions (H_β) of preasphaltenes. After the catalytic hydromodification, the longer side chains or bridge bonds break and are hydrogenated to form the aliphatic structures with a shorter chain or a higher branched degree. Meanwhile, more oxygen-containing functional groups were removed along with the reduction of volatiles in the modified coal. The synergistic effect of FeS on these factors is favorable for the generation of plastic materials, which contributes to the development of the caking property of lignite.

Although the preparation of coal-based carbon nanotubes (CNTs) has been realized in many studies, the relationship between carbon source structure of coal and CNT growth has not been studied in depth. In this study, we used lignite and KOH as raw material and catalyst and tuned lignite structure via hydrothermal modification to promote the formation of CNTs during catalytic pyrolysis. The main carbon source of CNTs was explored from the change of coal structure and pyrolysis characteristics. The results indicate that the CNT yield of lignite pyrolysis products is only 2.39%, but the CNT yield increases significantly after lignite was hydrothermally modified in a subcritical water-CO system. The graphitization degree, the order degree, and CNT content increase continuously with the increase in modification temperature, and C-M₃₄₀ has the highest CNT content of 9.41%. Hydromodification promotes the rearrangement of aromatic carbon structures to generate more condensed aromatic rings linked by short aliphatic chains and aromatic ether bonds. The variation of these structures correlates well with the formation of CNTs and leads to the change in the carbon source components released during coal pyrolysis. Compared to lignite, modified coal releases more aromatic compounds, especially polycyclic aromatic hydrocarbons with ≥3 rings and phenols during catalytic pyrolysis, which is conducive to the transformation into carbon clusters and provides carbon sources for CNT growth. In addition, modified coal releases a slightly more carbon-containing gas (CH₄ and CO) than lignite, which has a limited effect on the growth of CNTs. This study provides a novel and efficient method for enhancing the growth of CNTs by a molecular tailoring strategy of coal.