Methane, a primary component of natural gas, shale gas, biogas, and gas hydrates, constitutes a vast hydrogen-rich resource for production of high-value chemicals. However, its intrinsic chemical inertness poses significant challenges for catalytic conversion, primarily due to high activation barriers and severe carbon deposition (coking). These challenges result in rapid catalyst deactivation and reduced selectivity, thereby hindering industrial viability. Consequently, developing high-performance catalytic systems for methane conversion is of strategic importance against the backdrop of global chemical industry upgrading and the demand for efficient energy utilization. While emerging externally driven strategies, including thermocatalysis, photothermal catalysis, and photo-electrocatalysis, enable methane conversion under milder conditions, managing complex carbon deposition remains a persistent challenge. This review systematically categorizes the formation mechanisms of carbon species under both oxidative and non-oxidative environments. Performances of various catalytic systems are examined, ranging from solid-state thermocatalytic and photocatalytic materials to molten-phase frameworks. Special attention is devoted to active site design and metal-support interface engineering as key determinants of carbon resistance, catalytic stability, and product selectivity. Furthermore, mitigation strategies are critically evaluated. Finally, this review outlines future opportunities through the integration of structural optimization, kinetic modulation, field-assisted catalysis, and intelligent design to develop robust, selective, and long-life catalysts for methane valorization.

Electrocatalytic nitrate reduction reaction (NO₃RR), as a green technology for producing ammonia and purifying wastewater, faces challenges in terms of nitrite intermediate accumulation and competitive hydrogen evolution reactions. Tandem catalytic strategy (NO₃^-→NO₂^-→NH₃) is expected to significantly improve the rate and selectivity of ammonia production. Therefore, designing and constructing dual active sites with different catalytic properties contributes to improving reaction activity. Herein, a CuNi bimetallic metal organic framework (MOF) tandem catalytic system using well-defined MOFs as templates was constructed through simple hydrothermal synthesis. The research results indicated that Cu active sites could efficiently catalyze the reduction of NO₃^- to NO₂^-, while Ni sites exhibited excellent active hydrogen species ^*H supply capacity and NO₂^- conversion efficiency, forming an efficient tandem catalytic mechanism with Cu sites, and achieving a Faraday efficiency of up to 90.1% for ammonia synthesis and an ammonia yield of 28.8 mg·h^-1·mg_cat^-1. In addition, the bimetallic MOFs catalyst showed excellent cycling stability without any degradation in ammonia synthesis after multiple cycling tests. This work provides new insights for the design and optimization of high-performance tandem catalysts.

Methane (CH₄), as both a greenhouse gas and a crucial energy source, plays an important role in achieving China’s carbon peaking and carbon neutrality goals. The significant concentration differences of CH₄ from various sources influence the selection of relevant conversion technologies. However, little research has addressed the impact of CH₄ concentration variation on catalytic performance, and studies focusing on the catalytic pyrolysis of methane for carbon material production are especially scarce. In this work, molten salt catalytic pyrolysis was employed as the core strategy to systematically investigate the catalytic decomposition behavior of CH₄ with varying concentrations (20%-100%) and the morphology control mechanisms of carbon products in a CuCl₂-NaCl molten salt system. The results revealed that the formation of graphene films was attributed to the two-dimensional assembly of carbon atoms on bubble surfaces at high CH₄ concentrations, followed by subsequent film growth. High CH₄ concentration in the CuCl₂-NaCl system favored the formation of well-ordered graphene structures, while low concentrations primarily produced fragmented carbon. Furthermore, various molten salt systems yielded different carbon morphologies, including graphite sheets, short rod-like carbon nanotubes, and film-like carbon. Comprehensive characterizations demonstrated that the CH₄ concentration determined growth mode of the carbon products. This study elucidates morphology control mechanisms of the carbon products driven by the CH₄ concentration gradient in molten salt systems, providing a theoretical basis for the environmentally friendly synthesis of high-value-added carbon materials and development of low-carbon technologies.

Nitrogen oxides (NO_x), as main atmospheric pollutants in China, are usually removed through ammonia selective catalytic reduction (NH₃-SCR) technology to achieve ultra-low emissions. Low-temperature NH₃-SCR has gained much attention due to its low energy consumption and cost. However, MnO_x-based catalysts generally suffer from insufficient stability and are susceptible to SO₂ and H₂O poisoning at 120 ℃. To improve the denitrification performance of MnO_x-based catalysts under low temperature and lean flue gas conditions, CeO₂/MnO_x catalysts were prepared by precipitation-calcination decomposition method in this study. Influence of CeO₂ modification on structure, surface properties and low-temperature NH₃-SCR performance of catalyst was systematically studied. Combining first principles calculations, influence of CeO₂ modification on catalytic mechanism for reducing activation energy of the reaction was revealed at microscopic level. The results showed that addition of CeO₂ refined micro particle size of catalyst, reduced proportion of main crystalline phase MnO₂, significantly increased concentration of weak acid sites in the catalyst, augmented proportion of Mn³⁺/Mn and O_α/O, and improved surface acidity and redox performance of the catalyst. The prepared Mn10Ce3 and Mn10Ce5 catalysts achieved a NO conversion rate of over 98%, maintaining stability even at 120 ℃. Addition of CeO₂ dispersed the aggregated MnO_x and reduced concentration of Mn⁴⁺ distribution, which to some extent hindered excessive oxidation of NH₃ and NO by high valence Mn⁴⁺, thereby suppressing N₂O formation and improving N₂ selectivity of the catalyst. First principles calculations further confirmed that CeO₂ modification reduced the activation energy of various intermediate states in reaction pathway, lowering the reaction temperature and improving the low-temperature NH₃-SCR efficiency.

Spent hydrogenation catalysts are an important source of regeneration catalysts due to their large waste volume and high particle integrity. Most of the existing recovery technologies focusing on recovering valuable metals limit studies on the recovery of carrier particles. This study addresses the key challenge of ineffective classification of rod-shaped spent catalyst particles via traditional sieving due to their length-to-diameter ratios exceeding standard specifications. A fluidized bed classification process is innovatively proposed, and a coupled computational fluid dynamics (CFD) and discrete element method (DEM) simulation combined with response surface methodology (RSM) is employed to systematically elucidate the intrinsic mechanisms and optimization principles of fluidized bed classification. The results demonstrate that a fluidized bed enables efficient classification of particles with varying aspect ratios via gas-solid fluidization. Gas velocity is identified as the dominant factor influencing classification efficiency, followed by feed flow, whereas inlet height exhibits a negligible impact. A critical feed flow threshold exists under specific gas velocity and inlet height; exceeding this threshold leads to a decline in classification efficiency. By establishing a Box-Behnken design (BBD) model, optimal conditions are identified as a gas velocity of 10.45 m/s, a feed flow of 7.50 t/h, and an inlet height of 3.50 m, achieving 100% classification efficiency. This study clarifies the multi-physics coupling mechanism in fluidized bed classification and provides theoretical guidance for pre-classification processes of carrier particles during spent hydrogenation catalyst recycling.

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.