Methane pyrolysis is a technology that utilizes fossil energy to produce high added value carbon materials and hydrogen. However, traditional methods, such as chemical vapor deposition (CVD) and molten metal catalysis, face challenges in the production of graphene, including catalyst deactivation, difficulty in separating graphene from the catalyst, and high reaction temperatures (≥1100 ℃), which limit their industrial applications. This study proposes an innovative approach to produce graphene by catalyzing methane pyrolysis using Cu and metal oxides-KCl molten medium. By adding metal oxides (Al₂O₃, TiO₂, ZrO₂, MgO, SiO₂) as dispersants, the dispersion of active Cu sites is enhanced. Notably, Cu/ZrO₂ with a Cu content of 50% (in volume) and Cu/MgO with a Cu content of 75% (in volume) catalysts enable the efficient production of few-layer graphene. Cu/ZrO₂ catalyst with a Cu content of 50% (in volume) exhibits the highest activity, achieving a methane conversion rate of 22%, a hydrogen production yield of 21.5 mmol/h, and formation of large-area and smooth few-layer graphene. This study provides a new technical route for co-production of graphene and hydrogen via methane pyrolysis, offering potential for large-scale graphene production in the future.

Microporous structure is crucial to the properties and applications of porous carbon materials, but how to modulate it by an ion catalyst faces a complex situation. Here, a uniform porous carbon was obtained from phenolic resin/ethylene glycol through polymerization-induced phase separation (PIPS) method. Meanwhile, the influences of Zn²⁺ content and curing temperature on the microporous structure of porous carbon were studied. Regarding curing temperature, it was observed that the stability of porous carbon decreased with increasing temperature, adversely affecting the uniformity of microporous structure. At a curing temperature of 90 ℃, porosity, mean pore size, and median pore size of the porous carbon varied from 40.22% to 70.38%, 49.8 nm to 279.4 nm, and 107.2 nm to 343.0 nm, respectively. Concerning Zn²⁺ content, an initial increase was noted in porosity, median pore size and average pore size of the porous carbon with rising Zn²⁺ content, followed by a decrease. Specifically, with 1.5% (in mass) Zn²⁺, the maximum pore size and porosity reached 343.0 nm and (70.38±0.37)%, respectively. These findings show that addition of Zn²⁺ increases the curing degree and backbone polymerization, which may be attributed to a reduction in the reaction barrier for interstitial substitution of phenol structures. However, excessive Zn²⁺ content leads to high polymerization levels in the resin mixture, impeding volatilization of the alcohol-rich phase and thus degrading the pore structure. In addition, introduction of Zn²⁺ promotes graphitization, resulting in a more pronounced carbon skeleton than that of non-introduced sample. This research provides a theoretical basis for modulating the microstructure of porous carbon materials and preparation of structural carbide ceramics.

Nowadays, we are facing increasingly serious energy and environmental problems, which urgently need more efficient chemical industry technologies to meet the requirements of low cost, high yield and sustainability. Developing efficient catalysts is of great significance for improving production efficiency, expanding economic benefits, optimizing energy structure, and ameliorating industrial structure. Single-atom catalysts (SACs), featuring unique properties arising from their single-atom dispersion on support surface, have demonstrated exceptional activity, selectivity and stability in energy catalysis, environmental catalysis and organic catalysis. Therefore, preparation methods and catalytic mechanisms of SACs have become a hot research topic on the international catalytic community. This review describes three strategies for preparing SACs: bottom-up synthesis, top-down synthesis and quantum dots cross-linking/self-assembly. Specifically, methods such as co-precipitation, immersion, atomic layer deposition, high-temperature atom thermal transfer, and high-temperature pyrolysis are presented in detail. These approaches precisely control the location and distribution of metal atoms, maximizing their utilization and catalytic efficiency. In addition, the challenges and development prospects faced by SACs related to stability, integrated control and industrial scalability are also summarized.

Direct polymerization of CO₂ with diols for synthesis of carbonates represents a sustainable and efficient approach for CO₂ utilization, in which CeO₂ exhibits favorable catalytic properties in the reaction system. In this study, nanometer-sized CeO₂ catalysts were synthesized via a hydrothermal method utilizing NaOH as precipitating agent. The effects of sintering temperatures (500, 600, and 700 ℃) and surfactants (cationic, anionic, and nonionic) on structural and physicochemical properties of CeO₂ were thoroughly investigated. When the sintering temperature was 600 ℃, CeO₂ displayed an optimal crystallinity and a higher concentration of defect sites compared to the other temperatures. The surfactants significantly increased oxygen vacancy concentration on the surface of CeO₂, leading to a maximum CO₂ uptake of 0.532 mmol/g at 25 ℃. Building upon these findings, a series of synthesized CeO₂ catalysts were applied in the one-step synthesis of polycarbonate from CO₂ and diol, resulting in significant improvements in both conversion and selectivity within the reaction system. The results demonstrated that catalytic activities of CeO₂ prepared at various sintering temperatures with different surfactants displayed notable differences. Notably, the CeO₂ catalyst sintered with cetyltrimethylammonium bromide (CTAB) as the surfactant at 600 ℃ exhibited the highest catalytic activity and selectivity, achieving a conversion of 91.0% for 1,6-hexanediol and a selectivity of 76.6% for poly(6-hydroxyhexyl) carbonate. The outstanding catalytic performance of CeO₂ with the high yield can be primarily attributed to its favorable structural characteristics, abundant defect sites, and high CO₂ uptake capacity.

Ortho to para hydrogen conversion catalyst (O-P catalyst) is integral for large-scale hydrogen liquefaction projects. However, factors that influence catalyst performance remain preliminary and unclear. In the mean time, the mechanical strength of the O-P catalyst is crucial for its efficacy and longevity, yet most related research has paid sufficient attention to the catalytic activity. In this work, an iron-based O-P catalyst was synthesized using a straightforward precipitation method. And effects of catalyst activation method, drying temperature, particle size, concentration ratio, and doping element on catalytic activity and mechanical strength were studied. Furthermore, the catalytic performance and structural characterization of the prepared catalyst and commercial catalyst were compared. The prepared catalyst achieved a para hydrogen (p-H₂) content of 46.49% post-conversion at 77 K with a hydrogen flow rate of 1200 mL/min, surpassing the commercial catalyst by 2.9%. The maximum single particle crushing force of the prepared catalyst reached 4.75 N. Therefore, a preliminary mechanism for enhancing catalytic activity optimization was elucidated, offering valuable insights into ortho to para hydrogen conversion, and this study provides foundational data supporting the scaled production of domestic catalysts.

Ammonia serves not only as a primary raw material in synthetic fertilizers, but also as a novel high-energy- density fuel. In recent years, electrocatalytic nitrate reduction for ammonia synthesis has gained extensive attention as a green and sustainable approach due to its potential as an eco-friendly and sustainable way that could replace the energy-intensive and high-carbon-emission Haber-Bosch process. Nevertheless, the efficient electrocatalytic ammonia synthesis is still hampered by low reaction efficiency and product selectivity as well as catalyst stability. Hence, there is a pressing need to develop efficient catalysts to advance electrocatalytic nitrate reduction for ammonia synthesis. Recently, metal oxide catalysts have been at the center of attention for their superior performance in electrocatalytic nitrate reduction for ammonia synthesis. This review consolidates the developments of metal oxide electrocatalysts converting nitrate to ammonia, focusing on elucidating the reaction mechanism and introducing typical metal-based (Cu, Fe, Ti, etc.) catalysts. Additionally, it discusses the latest research progress in enhancing catalytic reaction efficiency, product selectivity, and material stability through strategies like morphology control, surface reconstruction, oxygen vacancy engineering, element doping, metal-assisted catalyst loading, etc. Finally, the paper outlines the challenges and future research directions in the realm of electrocatalytic nitrate reduction for ammonia synthesis.

Synthesis of ZSM-5 zeolite typically utilizes small molecule polyamines or quaternary ammonium salts as organic structure guiding agent (OSDA). By contrast, the OSDA-free hydrothermal synthesis system eliminates the use of organic templates and the subsequent calcination procedure. This not only reduces the cost of synthesis, but also prevents environmental pollution from the combustion of organic templates, representing an eco-friendly approach. Despite this, literature suggests that even so-called template-free synthesis systems often involve trace amount of organic substances like alcohol. In the present work, a calcined commercial ZSM-5 zeolite was served as seed, with sodium aluminate as aluminum source and silica sol as silicon source, ensuring an entirely template-free synthesis system. Polycrystalline ZSM-5 aggregates consisted of rod-like nanocrystals were successfully prepared in the completely OSDA-free system. Effects of the Si/Al ratio in ZSM-5 seed, dosage and crystallization conditions such as crystallization temperature and crystallization time on ZSM-5 synthesis were investigated. The results show that a highly crystallinity ZSM-5 aggregate consisting of primary nano-sized crystals less than 100 nm is produced from a gel precursor with 5.6% (in mass) seed after hydrothermal treatment for 48 h. Furthermore, the Si/Al ratio in ZSM-5 seed has little effect on the topological structure and pore structure of the synthesized samples. However, the seeds with a low Si/Al ratio facilitate faster crystallization of zeolite and enhance the acidity, especially the strong acid centers, of the catalyst. The catalytic performance of the synthesized polycrystalline ZSM-5 was evaluated during dehydration of methanol and compared with a commercial reference ZSM-5r. The results exhibit that as compared with the reference catalyst, the fabricated sample has a longer catalytic lifetime (16 h vs 8 h) attributed to its hierarchical pores derived from the loosely packed primary nanoparticles. Additionally, the prepared polycrystalline catalyst also exhibits a higher aromatics selectivity (28.1%-29.8% vs 26.5%).

In the industrial landscape, the well-established Haber-Bosch method is employed for the catalytic synthesis of ammonia (NH₃) from hydrogen and nitrogen gases, necessitating elevated temperatures (400-600 ℃) and high pressures (150-300 atm, 1 atm= 0.101325 MPa). In response to the imperative to reduce energy consumption and environment impact imposed by this synthetic process, significant research efforts have converged on realizing NH₃ synthesis under ambient conditions. This study delves into the realm of N₂ electrocatalytic reduction to NH₃, using density functional theory (DFT) calculations to explore the feasibility of employing graphene co-doped with a combination of transition metal elements (e.g., Fe, Nb, Mo, W, and Ru) and non-metal elements (e.g., B, P, and S) as catalyst for ammonia synthesis. The findings underscore that Mo and S co-doped graphene (Mo/S graphene) demonstrates an exceptionally low electrode potential of 0.47 V for NH₃ synthesis, with the key rate-controlling step centered around the formation of the intermediate *NNH. Especially, the ammonia synthesis potential is found to be lower than the hydrogen evolution potential (0.51 V), conclusively affirming the selectivity of nitrogen reduction to ammonia. Furthermore, through ab initio molecular dynamics calculations, the study attests to the remarkable thermodynamic stability of the Mo/S co-doped graphene system under room temperature conditions. Notably, electronic structure analysis validates that the ability of electron communication of the transition metal plays a pivotal role in dictating the efficiency of N₂ electrocatalytic reduction. It can be tactically optimized through controlled modulation of the influence of the non-metal element on the coordination environment of the transition metal, thus substantially enhancing catalytic performance.

Manganese and cerium oxides are extensively used for selective catalytic reduction (SCR) in denitrification reaction due to their high redox ability and excellent low-temperature SCR activities. However, these catalysts still face problems such as easy aggregation of active components and low specific surface area, which restricts the enhancement of catalytic activity. Here, graphene based SiO₂ nanocomposites (G@SiO₂) with mesoporous structure was used as the template to prepare series of graphene based mesoporous manganese-cerium oxides (G@MnO_x-CeO₂) catalysts by hydrothermal method. The obtained catalysts were investigated for selective catalytic reduction (SCR) of NO at low temperature (100-300 ℃). The results indicate that G@MnO_x-CeO₂ catalyst exhibits better SCR activity than graphene based cerium oxides (G@CeO₂). With the mass ratio of Mn and Ce to G@SiO₂ of 0.35 and 0.90, respectively, the G@Mn(0.35)Ce(0.9) catalyst shows the best NO removal activity with the maximum conversion of 80% at 220 ℃. It is found that the addition of appropriate amount of MnO_x increases specific surface area and pore volume but decreases crystallinity of the catalyst G@MnO_x-CeO₂. Furthermore, MnO_x and CeO₂ are uniformly distributed on the surface of graphene sheets in the form of nanoparticles. In addition, partial replaced Ce atoms is actually doped with Mn atoms into the structure of CeO₂ to form MnO_x-CeO₂ solid solution, resulting in higher percentage of Mn³⁺and Mn⁴⁺ with higher valance states and Ce⁴⁺, and higher concentration of surface chemisorbed oxygen on the surface. These results contribute to higher SCR activity of the G@Mn(0.35)Ce(0.9) catalyst. This work provides promising basic data for the practical application of MnO_x-CeO₂ based catalysts in low temperature NH₃-SCR.