Mechanism Of Carbon Formation Research Articles

Triphenylene-derived oxygen-enriched hierarchical porous carbon nanosheets: Carbonization mechanism and application in zinc-ion hybrid capacitors

Since zinc-ion hybrid capacitor (ZIHC) was first proposed, it has become an international study hotspot in the field of secondary energy for some time. Unfortunately, the unsatisfactory specific capacity of ZIHCs has limited its application in industrial development. Thus, there is an urgent need to synthesize carbon cathode with abundant pore structure and heteroatoms to construct high performance ZIHCs. Herein, we investigate the mechanism of FeCl3-induced carbon formation of triphenylene using FeCl3 as a catalyst and template. And the oxygen-enriched hierarchical porous carbon nanosheets with large specific surface area and abundant pores are successfully synthesized with the assistance of KOH activation strategy. Due to the addition of FeCl3 and KOH, the hierarchical porous carbon nanosheets have a unique pore structure and extremely high pore volume, and oxygen atoms are introduced to provide additional pseudocapacitance. As expected, ZIHCs constructed with the best sample exhibits an impressive specific capacity of 134.1 mAh g−1, a distinguished energy density of 102.04 Wh kg−1 (80 W kg−1) and outstanding cycling stability. This work clearly elucidates the carbon formation mechanism of triphenylene under the catalytic action of FeCl3, and provides another insight for the preparation and optimization of porous carbon for ZIHCs cathode.

Microbial-explicit processes and refined perennial plant traits improve modeled ecosystem carbon dynamics

Globally, soils hold approximately half of ecosystem carbon and can serve as a source or sink depending on climate, vegetation, management, and disturbance regimes. Understanding how soil carbon dynamics are influenced by these factors is essential to evaluate proposed natural climate solutions and policy regarding net ecosystem carbon balance. Soil microbes play a key role in both carbon fluxes and stabilization. However, biogeochemical models often do not specifically address microbial-explicit processes. Here, we incorporated microbial-explicit processes into the DayCent biogeochemical model to better represent large perennial grasses and mechanisms of soil carbon formation and stabilization. We also take advantage of recent model improvements to better represent perennial grass structural complexity and life-history traits. Specifically, this study focuses on: 1) a plant sub-model that represents perennial phenology and more refined plant chemistry with downstream implications for soil organic matter (SOM) cycling though litter inputs, 2) live and dead soil microbe pools that influence routing of carbon to physically protected and unprotected pools, 3) Michaelis-Menten kinetics rather than first-order kinetics in the soil decomposition calculations, and 4) feedbacks between decomposition and live microbial pools. We evaluated the performance of the plant sub-model and two SOM cycling sub-models, Michaelis-Menten (MM) and first-order (FO), using observations of net ecosystem production, ecosystem respiration, soil respiration, microbial biomass, and soil carbon from long-term bioenergy research plots in the mid-western United States. The MM sub-model represented seasonal dynamics of soil carbon fluxes better than the FO sub-model which consistently overestimated winter soil respiration. While both SOM sub-models were similarly calibrated to total, physically protected, and physically unprotected soil carbon measurements, the models differed in future soil carbon response to disturbance and climate, most notably in the protected pools. Adding microbial-explicit mechanisms of soil processes to ecosystem models will improve model predictions of ecosystem carbon balances but more data and research are necessary to validate disturbance and climate change responses and soil pool allocation.

Formation of carbon with a diamond-like lattice during the production of spinel MgAl2O4 by a combustion synthesis

Magnesium aluminate spinel (MAS) containing a carbon impurity was prepared by self-propagating high-temperature synthesis (SHS). Periclase MgO, alumina Al2O3, fuel Al powder, 2 wt% boron, and oxidizer Mg(NO3)2·6H2O were used as starting reagents for MAS synthesis. The phase composition of original boron and synthesized products, the structure and surface morphology of the samples were investigated. EDS analysis and elemental mapping confirmed that the impurity detected as crystals formed during the synthesis was carbon. IR spectroscopy showed that the carbon detected in the synthesized product has a diamond-like lattice similar to that of detonation diamonds. The analysis of gases evolved during combustion was performed. A proton‑boron reaction is shown to take place during fast self-propagating high-temperature synthesis of spinel. The probable mechanisms of carbon formation in the synthesis products are proposed using the experimental data.

Recent Research Progress on Black Carbon Emissions from Marine Diesel Engines

Black carbon (BC) emissions from shipboard diesel engines are the next potentially important issue of interest to the International Maritime Organization (IMO) and are considered to have a significant impact on the climate environment and human health. However, theories and technologies regarding the mechanisms of black carbon formation, oxidizing and influencing factors, emission detection methods, and abatement techniques are still missing in science and engineering. This paper provides a comprehensive overview of relevant advances in international maritime regulations, the frontier theory on formation mechanisms, comprehensive physical and chemical properties, and the potential reduction measures and control measures of emissions. These results suggest that BC is produced in the combustion flame of fuel and is related to the nucleation as well as the formation of PAHs. It helps to understand the initial generation process of black carbon and reduce its emission by studying it in detail and revealing some key factors, including micromorphology, nanostructural features, surface functional groups, oxidizing activity, size distribution, and elemental composition. Further, an in-depth understanding of the complex characteristics of BC can also help to identify viable BC measurement techniques and instrumentation for marine engines, thereby enhancing emission regulation. Overall, extensive technology can reduce BC emissions from marine diesel engines by approximately 50%. The information contained in this report can be used as a significant reference to further explore the BC formation mechanism and develop exclusive BC emission control strategies.

Magnetic carbon formation via in-situ CO2 capture and electrolysis in a molten carbonate system

CO2 gas has been used as a feedstock to demonstrate the effectiveness of direct CO2 electrolysis for the generation of value-added carbon products from problematic greenhouse gas. Iron-based materials act as low-cost catalysts in the synthesis of graphitic carbon in several electrochemical applications for conversions of CO2 to carbonaceous substances, however limited attention has been given to the influence of this abundant material on deposition outcomes. It was therefore the aim here to observe cathodic behaviour of iron in a high-temperature electrolysis system and compare its performance with an alloyed iron (stainless steel) cathode. In this work, a eutectic ternary (Li, Na, K)2CO3 electrolyte at a mild temperature of 600 °C has been used as the reduction process medium while capturing CO2 to regenerate carbonate. The electrolytic carbon products have been extensively characterized by different tests to determine physical and chemical properties of products formed. The impact of temperature and thermal cycling of electrolytes on the electrodeposition process have also been studied. Carbon with magnetic properties has been synthesized using a bulk iron cathode at a temperature of 600 °C, while employing alloyed iron inhibited the formation of magnetic carbon in similar experimental conditions. The mechanism of magnetic carbon formation on a bulk iron cathode has been explained to result from in-situ iron oxide formation on the surface of the cathode which is subsequently reduced to iron metal under reduction potential and subsequent inclusion of iron with the carbon products. This study provides a single-step process for synthesizing valuable magnetic carbon which not only used CO2 as the feedstock during its formation but has multiple value-added material applications.

Effect of forest planting patterns on the formation of soil organic carbon during litter lignocellulose degradation from a microbial perspective.

Litter decomposition is an important source of soil organic carbon, and it plays a key role in maintaining the stability of forest ecosystems. The microbial mechanism of soil organic carbon (SOC) formation in different urban forest planting patterns during litter lignocellulose degradation is still unclear. The key genes, microbes, and metabolites in the process of lignocellulose degradation and SOC formation were determined by metagenomics and metabolomics in different litter decomposition layers and soil layers in different urban forest planting patterns, including three types of broadleaf forests (BP forests), three types of coniferous forests (CP forests), and two types of mixed coniferous and broadleaf forests (MCBP forests). The results indicated that the cellulose, hemicellulose, and lignin concentrations from the undecomposed layer to the totally decomposed layer decreased by 70.07, 86.83, and 73.04% for CP litter; 74.30, 93.80, and 77.55% for BP litter; and 62.51, 48.58, and 90.61% for MCBP litter, respectively. The soil organic carbon of the BP forests and MCBP forests was higher than that of the CP forests by 38.06 and 94.43% for the 0-10 cm soil layer and by 38.55 and 20.87% for the 10-20 cm soil layer, respectively. Additionally, the gene abundances of glycoside hydrolases (GHs) and polysaccharide lyases (PLs) in the BP forests were higher than those in the MCBP forests and CP forests. Amino acid metabolism, sugar metabolism, TCA metabolism, and cAMP signaling metabolism were mainly between the CP forests and BP forests, while the TCA cycle, pyruvate metabolism, phenylalanine metabolism, and tyrosine metabolism were mainly between the BP forests and MCBP forests during litter decomposition. Additionally, ammonia nitrogen and hemicellulose were key factors driving SOC formation in the CP forests, while ammonia nitrogen, hemicellulose, and lignocellulose-degrading genes were key factors driving SOC formation in the BP forests. For the MCBP forests, cellulose, pH, ammonia nitrogen, and lignin were key factors driving SOC formation. Our findings revealed that the BP forests and MCBP forests had stronger lignocellulose degradation performance in the formation of SOC. This study provided a theoretical basis for the flow and transformation of nutrients in different urban forest management patterns.

Unlocking the mysteries: Investigating the kinetic mechanism of calcium carbonate formation from phosphogypsum

Apparent inconsistencies exist in the comprehensive utilization of sulfate, indicating a lack of systematic investigation into the relationships between reacting conditions and the structures of materials. This study quantifies the coprecipitation and transformation process during dissolution-carbonation from phosphogypsum (PG) to polymorphs of calcium carbonates (CaCO3) in the presence of NaOH, NH3, and CO2 through a two-step process. The research establishes a framework for characterizing resulting solutions and achieving products. Additionally, the kinetic mechanism of CaCO3 preparation and PG carbonation was established using a new atomistic KMC model, which reconciles discrepancies and predicts dissolution modes approaching equilibrium. Particularly, it predicts the structures and stability of CaSO4 hydrates by leveraging differential solubilities at a molecular level. Subsequent carbonation with CO2 and the calculation of equilibrium relationships under controlled conditions resulted in the production of CaCO3 from CaSO4·2 H2O. Model simulations and parameter optimization for precursors, intermediates, and generators were monitored and compared over time using RS and powder EPR experiments, yielding optical information for investigating the kinetic mechanism. The findings highlight that PG-involved pathways play a role in purification and mineralization, emphasizing the need to reevaluate traditional concepts of utilizing calcium-rich waste and capturing CO2.

The synergistic effect of biphenyl structure and N element in flame retardant and high value-added recycling of bio-based epoxy resin

Recently, growing concerns about climate change and environmental protection have increased interested in sustainable development of polymer materials. Here, ester-containing bio-based epoxy precursor was prepared, and was cured by 4, 4′-diaminodiphenylmethane (DDM). With the increase of DDM addition, the flame-retardant grade of the resins improved from V-1 to the highest V-0 in the vertical-burning tests. The results indicate that the increased N content was combined with biphenyl radicals and gradually formed thermally stable, nitrogen-rich char to insulate the matrix and improve flame retardancy after cyclization, rearrangement, and dehydrogenation process. Besides, considering the carbon formation mechanism, it was utilized as a potential precursor to prepare N, O dual-doped carbon by using KOH activation and pyrolysis method. The obtained porous carbons possess high CO2 adsorption performance (9.0 mmol g−1, 273 K), high CO2/N2 selectivity and good regenerability. Hence, this simple strategy offers an effective, durable, and environmentally friendly solution to increase the fire safety of epoxy resin, and also paves a way to close the loop from green synthesis to high value waste utilization of thermoset resin.

Enhancing the photocatalytic removal of toluene by modified porous TiO2 with internal hydrophobic interface

The efficiency and stability of photocatalytic oxidation techniques in the treatment of volatile organic compounds (VOCs) in the air are affected by the adsorption performance at the reaction interface and the photogenerated electron–hole separation efficiency. Carbon-loaded porous TiO2 with an internal hydrophobic interface was prepared by finely controlling the calcination time and temperature of a titanium-based metal–organic framework (MIL-125). The carbon load in the porous TiO2 presents a gradient from the pore surface to the interior. The formed hydrophobic interface in the channel avoids competitive adsorption between gas-phase toluene and H2O and effectively improves photogenerated electron transfer. Experiments and comprehensive analysis by using techniques such as thermogravimetric analysis, Raman spectroscopy, and ultraviolet diffuse-reflectance spectroscopy clarified the mechanism of gradient carbon formation in the porous TiO2, in which the organic ligands in MIL-125 are carbonized during calcination because of the low oxygen content of the pores. The sample prepared by pyrolyzing MIL-125 at 400 ​°C for 1 ​h showed the best activity in the photocatalytic degradation of toluene; the activity was twice that achieved with the commercial photocatalyst P25. Surface photovoltage spectroscopy and photoelectrochemical measurements proved that the gradient carbon load enhances photogenerated electron transfer in the porous TiO2. In-situ diffuse-reflectance infrared Fourier-transform spectroscopy was used to investigate the processes of photocatalytic degradation of toluene, in which the generation of C–H-containing intermediates is a crucial step. This research provides a novel concept for the future design and modification of photocatalyst structures for the effective photocatalytic degradation of VOCs.

DFT Investigations of the Reaction Mechanism of Dimethyl Carbonate Synthesis from Methanol and CO on Various Cu Species in Y Zeolites

In this study, a density functional theory method is employed to investigate the reaction mechanisms of dimethyl carbonate (DMC) formation, through oxidative carbonylation of methanol, on four types of Y zeolites doped with Cu+, Cu2+, Cu2O and CuO, respectively. A common chemical route is found for these zeolites and identified as, first, the adsorbed CH3OH is oxidized to CH3O species; subsequently, CO inserts into CH3O to CH3OCO, which reacts with CH3O to form DMC rapidly; and finally, the adsorbed DMC is released into the gas phase. The rate-limiting step on Cu2+Y zeolite is identified as oxidation of CH3OH to CH3O with activation barrier of 66.73 kJ·mol−1. While for Cu+Y, Cu2O-Y and CuO-Y zeolites, the rate-limiting step is insertion of CO into CH3O, and the corresponding activation barriers are 63.73, 60.01 and 104.64 kJ·mol−1, respectively. For Cu+Y, Cu2+Y and Cu2O-Y zeolites, adsorbed CH3OH is oxidized to CH3O with the presence of oxygen, whereas oxidation of CH3OH on CuO-Y is caused by the lattice oxygen of CuO. The order of catalytic activities of these four types of zeolites with different Cu states follows Cu+Y ≈ Cu2O-Y > Cu2+Y > CuO-Y zeolite. Therefore, CuY catalysts with Cu+ and Cu2O as dominated Cu species are beneficial to the formation of DMC.

Methane pyrolysis and carbon formation mechanisms in molten manganese chloride mixtures

Molten manganese chloride (MnCl2) is attractive as a high-temperature liquid catalyst for methane pyrolysis (CH4 → C + 2H2). Nevertheless, the mechanism of this reaction for continuously producing high-purity hydrogen and graphitic carbon from CH4 has not been fully elucidated. In this work, we investigated the reaction kinetics and mechanism of CH4 pyrolysis in mixtures of molten MnCl2 with various monovalent or divalent chlorides. The apparent activation energies of the molten MnCl2 mixtures for CH4 pyrolysis (<230 kJ mol−1) were much lower than that of the uncatalyzed reaction (400 kJ mol−1). Among the MnCl2 mixtures, only MnCl2–KCl showed a lower apparent activation energy than pure MnCl2 (152 and 172 kJ mol−1, respectively). In addition, MnCl2–KCl produced the largest amount of CH2* and the final solid carbon product with the highest crystallinity, suggesting that this system has unique CH4 dehydrogenation and carbon formation pathways. Density functional theory calculations also predicted high concentrations of CH2* in MnCl2–KCl, as confirmed by CH2 formation being more thermodynamically favorable in MnCl2–KCl than in MnCl2. Furthermore, the generation of C2+ unsaturated intermediates from CHx* (x < 3) was thermodynamically favored, suggesting a more facile pathway for the formation of graphitic carbon layers in molten MnCl2–KCl. In addition, an NVT ab initio molecular dynamics simulation suggested that gas-phase C–C coupling was facilitated in MnCl2–KCl by the frequent reversible desorption and adsorption of CHx* intermediates. These fundamental insights into the origins of the enhanced CH4 pyrolysis performance in MnCl2–KCl could aid in the development of molten salt catalysts with enhanced reactivity.

Soil Microbes from Saline–Alkali Farmland Can Form Carbonate Precipitates

The formation of soil inorganic carbon in saline–alkali lands is of great significance for enhancing soil carbon sequestration. As for the formation mechanisms, in addition to the discovered abiotic mechanisms, the microbial mechanisms remain unclear. To address this, soil microbes were isolated from the saline–alkali farmland of the Yellow River Delta in north China. Then, their capacity for carbonate precipitation formation was determined. Ten microbial strains were obtained from the soil. Of these, seven strains (four bacterial strains and three fungal strains), belonging to Rhodococcus sp., Pseudomonas sp., Bacillus sp., Streptomyces sp., Aspergillus sp., Cladosporium sp., and Trichoderma sp., formed carbonate precipitates in the range of 89.77~383.37 mg. Moreover, the formation of carbonate precipitates was related to specific metabolisms by which microbes can raise the pH (from 7.20 to &gt;8.00), suggesting that soil microbes that can enhance pH values by specific metabolisms containing the function of carbonate formation. Although an in situ experiment is needed to confirm such capacity, these results showed that soil bacteria and fungi existing in the saline–alkali farmland soil can form carbonate precipitates. The present study provided a microbial perspective for the mechanism of soil inorganic carbon formation, further implying a microbial potential of soil carbon sequestration in saline–alkali farmlands.

Phosphorus hotspots in pedogenic carbonate coatings determined by zoned microscale arrangement and organo-mineral interactions

Subsoils of calcareous soils are often characterized by pedogenic carbonate precipitates coating soil aggregate and rock surfaces. Numerous studies identified the key mechanisms of pedogenic carbonate formation in calcareous soils. Still, little is known about the ecosystem function of carbonate precipitates for nutrient supply, their microscale structure and the interaction of microscale structure with nutrient distribution such as P. We investigated the mineral composition and P speciation of lithogenic carbonate coated by pedogenic carbonate precipitates. Subsoil horizons of a Rendzic Leptosol (Tuttlingen, C horizon) and a Eutric Cambisol (Benediktenwand, BC horizon) in Central Europe were sampled. We combined wet-chemical methods with X-ray diffraction, synchrotron-based P XANES spectroscopy, and specific surface area analysis (N2-BET). To investigate the spatial arrangement and elemental distribution at the microscale, a complementary approach using light microscopy, scanning electron microscopy with energy dispersive x-ray spectroscopy (SEM-EDX) as well as XANES spectroscopy at the microscale (µXANES) was conducted. In both soils, the pedogenic carbonate coatings showed an intricate porous microstructure and large specific surface area. The δ13C values of the coatings were halfway between those of the primary bedrock and soil organic matter (SOM), proving their formation by re-precipitation of dissolved carbonate through organic and inorganic (H2CO3) acids. Compared to the primary rocks, the coatings were enriched in Al, Fe, Mn, and K and in organic C, N, and P; additionally, they contained silicate minerals (muscovite, illite) and quartz. Whereas the P in the rock interior was mainly present as apatite, the P in the coatings was mainly organic P bound to Ca and Al minerals. NanoSIMS and µXANES analyses at Tuttlingen revealed a zoned microstructure of the pedogenic coating: An inner zone with most P co-localized and bound to Al minerals and an outer zone enriched again in Ca and SOM. The formation of these zones indicates the infiltration and residual accumulation of Al minerals which may contribute to mitigate P losses by leaching. Intensive penetration by fine plant roots and observations of fungal hyphae within the coatings indicate the potential of pedogenically altered carbonates as microbial habitat and ecosystem nutrient source, thus contributing to the scarce ecosystem P nutrition of initial calcareous soils.

Recent Progress and Perspectives of Solid State Na-CO2 Batteries

Solid state Na-CO2 batteries are a kind of promising energy storage system, which can use excess CO2 for electrochemical energy storage. They not only have high theoretical energy densities, but also feature a high safety level of solid-state batteries and low cost owing to abundant sodium metal resources. Although many efforts have been made, the practical application of Na-CO2 battery technology is still hampered by some crucial challenges, including short cycle life, high charging potential, poor rate performance and lower specific full discharge capacity. This paper systematically reviews the recent research advances in Na-CO2 batteries in terms of understanding the mechanism of CO2 reduction, carbonate formation and decomposition reaction, design strategies of cathode electrocatalysts, solid electrolytes and their interface design. In addition, the application of advanced in situ characterization techniques and theoretical calculation of metal–CO2 batteries are briefly introduced, and the combination of theory and experiment in the research of battery materials is discussed as well. Finally, the opportunities and key challenges of solid-state Na-CO2 electrochemical systems in the carbon-neutral era are presented.

Fisher–Tropsch Synthesis for Conversion of Methane into Liquid Hydrocarbons through Gas-to-Liquids (GTL) Process: A Review

The interest in Gas-to-Liquid technology (GTL) is growing worldwide because it involves a two-step indirect conversion of natural gas to higher hydrocarbons ranging from Liquefied Petroleum Gas (LPG) to paraffin wax. GTL makes it possible to obtain clean diesel, naphtha, lubes, olefins, and other industrially important organics from natural gas. This article is a brief review discussing the state-of-the-art of GTL, including the basics of syngas manufacturing as a source for Fischer-Tropsch synthesis (FTS), hydrocarbons synthesis (Fischer-Tropsch process), and product upgrading. Each one is analyzed, and the main characteristics of traditional and catalysts technologies are presented. For syngas generation, steam methane reforming, partial oxidation, two-step reforming, and autothermal reforming of methane are discussed. For Fischer–Tropsch, we highlight the role of catalysis and selectivity to high molecular weight hydrocarbons. Also, new reactors technologies, such as microreactors, are presented. The GTL technology still faces several challenges; the biggest is obtaining the right H2:CO ratio when using a low steam-to-carbon ratio. Despite the great understanding of the carbon formation mechanism, little has been made in developing newer catalysts. Since 60–70% of a GTL plant cost is for syngas production, it needs more attention, particularly for developing the catalytic partial oxidation process (CPO), given that modern CPO processes using a ceramic membrane reactor reduce the plant’s capital cost. Improving the membrane’s mechanical, thermal, and chemical stability can commercialize the process. Catalytic challenges accompanying the FTS need attention to enhance the selectivity to produce high-octane gasoline, lower the production cost, develop new reactor systems, and enhance the selectivity to produce high molecular weight hydrocarbons. Catalytically, more attention should be given to the generation of a convenient catalyst layer and the coating process for a given configuration.

New insights into the early stage nucleation of calcium carbonate gels by reactive molecular dynamics simulations.

The precipitation of calcium carbonate (CaCO3) is a key mechanism in carbon capture applications relying on mineralization. In that regard, Ca-rich cementitious binders offer a unique opportunity to act as a large-scale carbon sink by immobilizing CO2 as calcium carbonate by mineralization. However, the atomistic mechanism of calcium carbonate formation is still not fully understood. Here, we study the atomic scale nucleation mechanism of an early stage amorphous CaCO3 gel based on reactive molecular dynamics (MD) simulations. We observe that reactive MD offers a notably improved description of this reaction as compared to classical MD, which allows us to reveal new insights into the structure of amorphous calcium carbonate gels and formation kinetics thereof.

Natural and Human-Induced Factors on the Accumulation and Migration of Pedogenic Carbonate in Soil: A Review

As a principal part of the atmosphere–lithosphere interface, soil plays a key role in regulating the atmospheric CO2 concentration and global climate. Comprising two major pools (carbonate in soils and bicarbonate in groundwater), soil inorganic carbon (SIC) is deemed as the primary carbon (C) sink and source in areas with low mean annual rainfall. SIC may originate from soil parent material or from the formation of secondary carbonate when divalent cations from an extraneous source are supplied. The latter may result in pedogenic carbonate (PC) formation, increasing soil C content and sequestering atmospheric carbon. Since the sequestration of atmospheric CO2 through formation of pedogenic carbonate is gaining popularity as a method to support climate change mitigation efforts and to claim carbon credits, the mechanisms influencing the formation and migration of pedogenic carbonate need to be well understood. The present review provides an overview of the available literature on potential natural and anthropogenic factors influencing the pedogenic carbonate pool in soils. Firstly, the overall mechanisms of pedogenic carbonate formation, as well as the control factors, are described. Secondly, the impact of various land-use changes on pedogenic carbon pool modification is discussed. Then, the potential of stabilizing atmospheric CO2 through PC formation and the challenges and techniques of tracking the formation of PC through engineered pathways in soils are explored. Finally, isotopic signature as a technique for distinguishing neo-formed carbonate in soil is scrutinized.

Electrodeposition of a Li-Al Layered Double Hydroxide (LDH) on a Ball-like Aluminum Lathe Waste Strips in Structured Catalytic Applications: Preparation and Characterization of Ni-Based LDH Catalysts for Hydrogen Evolution

A functionally structured catalyst was explored for ethanol steam reforming (ESR) to generate H2. Aluminum lathe waste strips were employed as the structured catalytic framework. The mixed metal oxide (Li-Al-O) was formed on the surface of Al lathe waste strips through calcination of the Li-Al-CO3 layered double hydroxide (LDH), working as the support for the formation of Ni catalyst nanoparticles. NaOH and NaHCO3 titration solutions were, respectively, used for adjusting the pH of the NiCl2 aqueous solutions at 50 °C when developing the precursors of the Ni-based catalysts forming in-situ on the Li-Al-O oxide support. The Ni precursor on the Al structured framework was reduced in a H2 atmosphere at 500 °C for 3 h, changing the hydroxide precursor into Ni nanoparticles. The titration agent (NaOH or NaHCO3) effectively affected the physical and chemical characterizations of the catalyst obtained by the different titrations. The ESR reaction catalyzed by the structured catalysts at a relatively low temperature of 500 °C was studied. The catalyst using NaHCO3 titration presented good stability for generating H2 during ESR, achieving a high rate of H2 volume of about 122.9 L/(gcat·h). It also had a relatively low acidity on the surface of the Li-Al-O oxide support, leading to low activity for the dehydration of ethanol and high activity to H2 yield. The interactions of catalysts between the Ni precursors and the Li-Al-O oxide supports were discussed in the processes of the H2 reduction and the ESR reaction. Mechanisms of carbon formation during the ESR were proposed by the catalysts using NaOH and NaHCO3 titration agents.

Decarbonizing Natural Gas: A Review of Catalytic Decomposition and Carbon Formation Mechanisms

In the context of energy conservation and the reduction of CO2 emissions, inconsistencies between the inevitable emission of CO2 in traditional hydrogen production methods and eco-friendly targets have become more apparent over time. The catalytic decomposition of methane (CDM) is a novel technology capable of producing hydrogen without releasing CO2. Since hydrogen produced via CDM is neither blue nor green, the term “turquoise” is selected to describe this technology. Notably, the by-products of methane cracking are simply carbon deposits with different structures, which can offset the cost of hydrogen production cost should they be harvested. However, the encapsulation of catalysts by such carbon deposits reduces the contact area between said catalysts and methane throughout the CDM process, thereby rendering the continuous production of hydrogen impossible. This paper mainly covers the CDM reaction mechanisms of the three common metal-based catalysts (Ni, Co, Fe) from experimental and modelling approaches. The by-products of carbon modality and the key parameters that affect the carbon formation mechanisms are also discussed.

Characteristics of phase formation during combustion of the MgO-Al2O3-Mg(NO3)2·6H2O-Al-B system

The research revealed the carbon micro traces in the synthesis products of magnesium aluminate spinel produced by the method of self-propagating high-temperature synthesis (SHS) in the MgO-Al2O3-Mg(NO3)2·6H2O-Al system with boron additives. The phase composition, structure, and morphological features of the surface of the samples were examined. The gases evolving during combustion were analyzed. IR spectroscopic analysis showed that carbon has a diamond-like lattice similar to the lattice of detonation nanodiamonds. It was shown that low-energy nuclear reactions (boron-proton reaction) proceed in the combustion wave during high-speed SHS processes under certain conditions. Based on the experimental data, the most probable mechanisms of carbon formation in the synthesized products were formulated and proposed.