Chemical Conversion Processes Research Articles

Promotion of Metal‐Free Catalytic Coupling of Fluorinated Halogenated Hydrocarbons By a Base for the Synthesis of Difluoromethyl Heterocyclic Amines

The selective functionalization of difluoromethyl groups (‐CF2) is a promising approach and an attractive synthetic route for accessing fluorine‐containing moieties with medicinal benefits. Here, we report a case of a C‒N coupling reaction between bromodifluoropropene with heterocyclic amines, such as indole, pyrrole, and imidazole, promoted by an alkali without the use of transition metal catalysis. This reaction differs from existing methods in that it does not undergo a difluoromethylation isomerization reaction but directly retains the structure of the terminal olefin. This chemical conversion process has a wide substrate range, good functional group tolerance, and an ideal reaction conversion rate, making it an effective new method for the difluoropropenation of heterocyclic amines.

Efficient synthesis of 2,5‐furandicarboxylic acid from corncob biomass using Ru/C and sulfonated carbon catalysts in a one‐pot system

AbstractThis study proposes a novel one‐pot method to produce 2,5‐furandicarboxylic acid (FDCA), which effectively simplifies the preparation process of FDCA by directly utilizing the biomass raw material corncob and its derived carbon‐based catalysts. In this work, we first prepared two different carbon‐based catalysts from corncobs: a ruthenium‐supported catalyst (Ru/C) and a sulfonated carbon catalyst. After detailed characterization and performance testing, these two catalysts were used to catalyze the pretreated corncob mixture to produce FDCA. Under optimized conditions, even using 0.12 g of Ru/C catalyst at a microwave power of 200 W, the yield of FDCA can reach 27 mol%. In comparison, the FDCA yield of the sulfonated carbon catalyst under the same conditions was 19 mol%. This work not only demonstrates the possibility of efficient production of FDCA by utilizing biomass resources and a simplified chemical conversion process, but also highlights the importance of selecting appropriate catalysts and controlling reaction conditions in improving yields. Through this method, we can promote the development of biomass conversion technology in a more efficient and environmentally friendly direction, providing technical support for the commercial production of bio‐based chemicals.

Thermolysis of Cs9MO4 (M = In, Sc): Synthesis, Crystal Structure, Chemical Bonding, and Reactivity of the Subvalent Oxidometalates Cs7MO4 (M = In, Sc).

The cesium-poor alkali-metal suboxidometalates Cs7MO4 (M = In, Sc) were prepared from the respective cesium-rich suboxidometalates Cs9MO4 by thermolysis in a dynamic vacuum at temperatures below 150 °C. They crystallize in a new structure type, comprising isolated tetrahedral oxidometalate anions [MO4]5- immersed in a matrix of metallic cesium atoms. This structural separation into alternating ionic and metallic building units is typical for subvalent compounds. Cs7InO4 and Cs7ScO4 are isotypic and form mixed crystals Cs7(In1-xScx)O4 with statistic distribution of In and Sc atoms. All compounds were characterized by single crystal and powder X-ray diffraction. Calculations of the electronic structure with DFT methods corroborate the coexistence of anionic entities within a metallic matrix and give evidence of the subvalent nature of cesium atoms. Overall metallic behavior is a consequence of the equal volume fractions of metallic and ionic regions, allowing for percolation of the conduction electrons throughout the crystal volume. Differential thermoanalysis was employed to gain insight into the chemical conversion processes during the thermolysis reaction. The thermolytic decomposition of Cs9MO4 is a multistep process with, in some instances, reversible amorphization and recrystallization steps. Finally, the formation of ionic compounds is observed. The full decomposition of Cs9ScO4 yields the two new oxidoscandates Cs14Sc4O13 and Cs17Sc5O15 with tetrahedral [ScO4] units connected to chain fragments and the indium compound yields cesium oxidoindates with low-condensed [InO4] building units. The cesium-poor suboxidometalates Cs7MO4 themselves can serve as starting materials for the synthesis of further, new suboxidometalates, as they show a unique reactivity toward metals.

Modeling Dipolar Molecules with PCP-SAFT: A Vector Group-Contribution Method.

Predicting thermodynamic equilibrium properties is essential to develop chemical and energy conversion processes in the absence of experimental data. For the modeling of thermodynamic properties, statistical associating fluid theory (SAFT)-based equations of state, such as perturbed-chain polar (PCP)-SAFT, have been proven powerful and found broad application. The PCP-SAFT parameters can be predicted by group-contribution (GC) methods. However, their application to the dipole term is substantially limited: current GC methods neglect the dipole term or only allow for a single dipolar group per substance to avoid handling the molecular dipole moment's symmetry effects. Still, substances with multiple dipolar groups are highly relevant, and their description substantially improves by including the dipole term in SAFT models. To overcome these limitations, this work proposes a vector-addition-based (Vector-)GC method for the dipole term of PCP-SAFT that accounts for molecular symmetry. The Vector-GC employs information on the substance's molecular 3D structure to predict the molecular dipole moment through a vector addition of bond contributions. Combining the proposed sum rule for dipole moments with established sum rules for the remaining parameters yields a consistent GC method for PCP-SAFT for dipolar substances. The prediction capabilities of the Vector-GC method are analyzed against experimental data for two substance classes: nonassociating oxygenated and halogenated substances. We demonstrate that the Vector-GC method improves vapor pressure and liquid density predictions compared to neglecting the dipole term. Moreover, we show that the Vector-GC method enables differentiation between cis- and trans-isomers. The Vector-GC method, hence, substantially increases the predictive capabilities and applicability domain of GC methods. All parameters are provided as JSON and CSV files, and the Vector-GC method is available through an open-source python package. Additionally, the developed regression framework for GC methods for PCP-SAFT is openly available. The regression framework can be employed to regress the Vector-GC method to other substance classes and is easily adaptable to other sum rules for PCP-SAFT.

Exploring the Facet-Dependent Structural Evolution of Pt/CeO2 Catalysts Induced by Typical Pretreatments for CO Oxidation.

Atomic-scale insights into the interactions between metals and supports play a crucial role in optimizing catalyst design, understanding catalytic mechanisms, and enhancing chemical conversion processes. The effects of oxide support on the dynamic behavior of supported metal species during pretreatments or reactions have been attracting a lot of attention; however, very less systematic integrations are carried out experimentally using real catalysts. In this study, we here utilized facet-controlled CeO2 as examples to explore their influence on the supported Pt species (1.0 wt %) during the reducing and oxidizing pretreatments that are typically applied in heterogeneous catalysts. By employing a combination of microscopy, spectroscopy, and first-principles calculations, it is demonstrated that the exposed crystal facets of CeO2 govern the evolution behavior of supported Pt species under different environmental conditions. This leads to distinct local coordinations and charge states of the Pt species, which directly influence the catalytic reactivity and can be leveraged to control the catalytic performance for CO oxidation reactions.

Production of Biofuels from Agricultural Waste

Agricultural waste represents a largely untapped resource that could be utilized for the production of biofuels through various conversion pathways. As the global demand for renewable and sustainable energy grows, biofuels offer solutions to mitigate climate change impacts while improving waste management. This review analyzes using agricultural residues and by-products as feedstocks for biofuel production through biological, thermochemical and chemical conversion processes. The different types of lignocellulosic biomass available from agricultural activities are discussed, along with their compositions. While agricultural waste has advantages like wide availability and low cost, challenges relating to heterogeneous composition, pre-existing contamination and seasonal availability must be addressed. Fermentation, anaerobic digestion, pyrolysis and gasification are examined as established routes for converting agricultural waste into liquid biofuels and biogas. Pretreatment methods, enzyme production pathways and synthesis of fuels like ethanol, butanol and diesel substitutes are outlined. Environmental benefits of biofuels from waste, including greenhouse gas mitigation and recycling of soil nutrients, are evaluated against fossil fuel alternatives. Case studies on operational plants and feasibility studies provide insights into technical and economic viability at scale. Challenges regarding feedstock logistics, conversion efficiency, commercial scale-up and sustainability assessment are identified for future research focus. In conclusion, the review finds that agricultural waste is a promising renewable resource for biofuel production when integrated with appropriate thermochemical, biochemical or anaerobic digestion technologies. While the field is advancing, further improvements in areas such as feedstock supply, pretreatment technologies, and demonstration of sustainability will be critical to realize the full potential of this emerging bioeconomy sector. The review recommends steps to accelerate commercialization and policy frameworks to incentivize waste-to-energy solutions.

High corrosion-resistance and electrical-conductivity phytic acid/permanganate composite coating on AZ31 magnesium alloy

A composite coating based on phytic acid and permanganate was developed on AZ31 magnesium alloy via two-step chemical conversion process, exhibiting high corrosion resistance and low contact resistance. The morphology, composition, anti-corrosion properties and electrical properties of the composite coating were characterized. The composite coating was mainly composed of magnesium phytate, MnO2 and Mn2O3. The corrosion protective efficiency of the composite coating is 80.25 %, which is higher than that of the phytic acid coating and potassium permanganate coating. Furthermore, the composite coating shows low electrical contact resistance around 0.083 Ω cm2, which is close to the potassium permanganate coating but much higher than the phytic acid coating. The high corrosion resistance and electrical conductivity of the composite coating can be attributed to the growth of conductive manganese oxide at the cracks or pores of the anti-corrosion phytic acid coating.

Simultaneously Regulating Electrochemical Corrosion Behavior and Wettability of Magnesium-Neodymium Alloy by Self-Layered Chemical Conversion Coating.

Rapid corrosion in aqueous solutions of magnesium alloys is one of the major obstacles to their wide application, and coating plays a crucial role in their corrosion protection. Recently, protection- and function-integrated coatings have attracted much attention in the research field of magnesium alloys. In this work, a simple chemical conversion process is proposed to fabricate a composite coating on a magnesium-neodymium alloy through immersion in an aqueous solution made of Ca(OH)2 and NaHCO3. After the immersion process, a coating consisting of two spontaneously formed layers is acquired. The top flower-like layer is composed of Mg5(OH)2(CO3)4∙4H2O, Mg(OH)2 and CaCO3, and the inner dense layer is speculated to be Mg(OH)2. Electrochemical impedance spectroscopy, polarization tests, and hydrogen evolution are combined to evaluate the corrosion resistance in simulated body fluid, simulated seawater solution, and simulated concrete pore solution, which reveals that the coated sample has better corrosion resistance than the uncoated one. After the coated sample is modified with fluorinated silane, a water-repellent surface can be achieved with an average water contact angle of 151.74° and a sliding angle of about 4°. Therefore, our results indicate that effective corrosion protection and potential self-cleaning ability have been integrated on the surface of the magnesium alloy in this study. In addition, the formation mechanism of the self-layered coating is discussed from the viewpoint of the interaction between the substrate and its external solution.

Marine Bacillus haynesii chitinase: Purification, characterization and antifungal potential for sustainable chitin bioconversion

The development of chitinase tailored for the bioconversion of chitin to chitin oligosaccharides has attracted significant attention due to its potential to alleviate environmental pollution associated with chemical conversion processes. In this present investigation, we purified extracellular chitinase derived from marine Bacillus haynesii to homogeneity and subsequently characterized it. The molecular weight of BhChi was approximately 35 kDa. BhChi displayed its peak catalytic activity at pH 6.0, with an optimal temperature of 37 °C. It exhibited stability across a pH range of 6.0–9.0. In addition, BhChi showed activation in the presence of Mn2+ with the improved activity of 105 U mL−1. Ca2+ and Fe2+ metal ions did not have any significant impact on enzyme activity. Under the optimized enzymatic conditions, there was a notable enhancement in catalytic activity on colloidal chitin with Km of 0.01 mg mL−1 and Vmax of 5.75 mmol min−1. Kcat and catalytic efficiency were measured at 1.91 s−1 and 191 mL mg−1 s−1, respectively. The product profiling of BhChi using thin layer chromatography and Mass spectrometric techniques hinted an exochitinase mode of action with chitobiose and N-Acetyl glucosamine as the products. This study represents the first report on an exochitinase from Bacillus haynesii. Furthermore, the chitinase showcased promising antifungal properties against key pathogens, Fusarium oxysporum and Penicillium chrysogenum, reinforcing its potential as a potent biocontrol agent.

Chemoenzymatic synthesis of (1R,3R)-3-hydroxycyclopentanemethanol: An intermediate of carbocyclic-ddA

The synthesis of carbocyclic-ddA, a potent antiviral agent against hepatitis B, relies significantly on (1R,3R)-3-hydroxycyclopentanemethanol as a key intermediate. To effectively produce this intermediate, our study employed a chemoenzymatic approach. The selection of appropriate biocatalysts was based on substrate similarity, leading us to adopt the CrS enoate reductase derived from Thermus scotoductus SA-01. Additionally, we developed an enzymatic system for NADH regeneration, utilising formate dehydrogenase from Candida boidinii. This system facilitated the efficient catalysis of (S)-4-(hydroxymethyl)cyclopent-2-enone, resulting in the formation of (3R)-3-(hydroxymethyl) cyclopentanone. Furthermore, we successfully cloned, expressed, purified, and characterized the CrS enzyme in Escherichia coli. Optimal reaction conditions were determined, revealing that the highest activity occurred at 45°C and pH 8.0. By employing 5mM(S)-4-(hydroxymethyl)cyclopent-2-enone, 0.05mM FMN, 0.2mM NADH, 10μM CrS, 40μM formic acid dehydrogenase, and 40mM sodium formate, complete conversion was achieved within 45min at 35°C and pH 7.0. Subsequently, (1R,3R)-3-hydroxycyclopentanemethanol was obtained through a simple three-step chemical conversion process. This study not only presents an effective method for synthesizing the crucial intermediate but also highlights the importance of biocatalysts and enzymatic systems in chemoenzymatic synthesis approaches.

Hydrogenation of Covalent Organic Framework Induces Conjugated π Bonds and Electronic Topological Transition to Enhance Hydrogen Evolution Catalysis.

Recently, many topological materials have been discovered as promising electrocatalysts in chemical conversion processes and energy storage. However, it remains unclear how the topological electronic states specifically modulate the catalytic reaction. Here, the two-dimensional metal phthalocyanine-based covalent organic framework (MPc-COF) is studied by ab initio thermodynamic calculations to clearly reveal the promotional effect on the electrochemical hydrogen evolution reaction (HER) induced by topological gapless bands (TGBs). We find that the prehydrogenated (and fluorinated) H4CdPc-COF(F) shows the best HER performance, with 0.016 V (near zero) overpotential. By tracking changes to the electronic structure and free energy as the prehydrogenation and HER processes occur, we are able to separately attribute the high HER efficiency in part due to the increase of the electron bath by donating electrons to the conjugated π bonds and also to the existence of TGBs. Specifically, the significant catalytic promotion by TGBs is proven to decrease the free energy by 0.218 eV to near zero. When the TGBs are destroyed, e.g., by replacing N with P and opening a band gap, the HER efficiency is reduced. This study opens avenues for deterministically harnessing topological band features to improve electrocatalysis.

Transforming Residual Lithium Compounds on the LiNi0.8Mn0.1Co0.1O2 Surface into a Li-Mn-P-O-Based Composite Coating for Multifaceted Improvements.

LiNi0.8Mn0.1Co0.1O2 (NMC811) is the most promising cathode material for next-generation lithium-ion batteries (LIBs). However, the chemical instability of the material during air exposure leads to the formation of residual lithium compounds (RLCs: LiOH and Li2CO3) on the surface and inhibits its practical application. Here, we propose a chemical conversion process to remove RLCs by utilizing them and forming a hybrid coating layer on the surface of NMC811 that contains Li3PO4, LiMn2O4, and LiMnPO4 phases, yielding multifaceted benefits. The hybrid layer on the surface protects the material from undesirable side reactions. It improves the cycle life of NMC811 by retaining 80% of its initial capacity after 300 cycles and 66% after 500 cycles at a 0.5C rate in the operating voltage of 3.0-4.3 V. The process enables high-voltage (4.7 V vs Li+/Li) operation by stabilizing the electrode-electrolyte interface, reduces the degree of cationic disorder and the voltage polarization for phase transitions, improves Coulombic efficiency and ion diffusion kinetics, and minimizes the secondary particle crack formation over long-term cycling. In fact, the coating reduces the detrimental effects of RLCs, leaves the surface for better Li+ transport, and hence significantly improves the electrochemical performance of NMC811.

Corrosion Behavior of Chromium Conversion Coated AZ91C Magnesium Alloy in Sodium Borate and Sodium Chloride Aqueous solutions

A chromium containing film was deposited on the surface of the investigated AZ91C magnesium alloy by chemical conversion process. The microstructure and surface morphology of the as- received and coated alloys were initially characterized by optical microscope. The corrosion behavior of AZ91C before and after coating was studied through weight loss technique by immersion in 3.5% NaCl and borate solutions at various concentrations and pH values. Surface corrosion products and passivation films were analyzed by X-ray diffraction. The obtained results showed that AZ91C coated with chromium conversion coating exhibits enhanced corrosion resistance, furthermore X-ray diffraction revealed that corrosion damage was mainly caused by formation of crystalline phase Mg(OH)2. The addition of borate with different concentration enhanced the protection with efficiency of 86% recorded at 0.2N sodium borate concentration and 3.5% NaCl.Corrosion behavior

Effects of Heterogeneous Sulfated Acid Photocatalysts and Irradiation of Ultraviolet Light on the Chemical Conversion and Characteristics of Antifreeze from Bioglycerol

The purity of crude glycerol, a by-product of biodiesel production, may be as low as 50%. Thus, it has relatively low economic value without previously applying adequate physical purification or chemical conversion processes. A solid-state sulfated acid photocatalyst, TiO2/SO42− was prepared in this study to catalyze the chemical conversion of bioglycerol with acetic acid to produce an antifreeze of glycerine acetate to improve the low-temperature fluidity of liquid fuel. The experimental results show that similar X-ray intensity structures appeared between the catalysts of TiO2/SO42− and SO42−. An infrared spectra analysis using a Fourier transform infrared (FTIR) spectrometer confirmed the successful sintering of SO42− and ligating with TiO2 for preparing TiO2/SO42−. The effects of the photocatalyst were further excited by the irradiation of ultraviolet light. The highest weight percentage of glycerine acetate was obtained under a reaction time and reaction temperature of 10 h and 120 °C, respectively. In addition, it was observed that the glycerol conversion ratio reached 98.65% and the triacylglycerols compound amounted to 40.41 wt.% when the reacting molar ratio was 8. Moreover, the freezing point of the product mixture of glycerine acetate under the same molar ratio reached as low as −46.36 °C; the lowest among the products made using various molar ratios of acetic acid/glycerol. The UV light irradiation rendered higher triacylglycerols and diacylglycerols with lower diacylglycerol formation ratios than those without light irradiation.

FROM NOVEL COATING STRATEGY ON BIODEGRADABLE MG-BASED ORTHOPAEDIC IMPLANT MATERIAL TOWARDS CLINICAL TRIAL

Device-associated bacterial infections are a major and costly clinical challenge. This project aimed to develop a smart new biomaterial for implants that helps to protect against infection and inflammation, promote bone growth, and is biodegradable. Gallium (Ga) doped strontium-phosphate was coated on pure Magnesium (Mg) through a chemical conversion process. Mg was distributed in a graduated manner throughout the strontium-phosphate coating GaSrPO4, with a compact structure and a Ga-rich surface. We tested this sample for its biocompatibility, effects on bone remodeling and antibacterial activities including Staphylococcus aureus, S. epidermidis and E. coli - key strains causing infection and early failure of the surgical implantations in orthopaedics and trauma.Ga was distributed in a gradient way throughout the entire strontium-phosphate coating with a compact structure and a gallium-rich surface. The GaSrPO4 coating protected the underlying Mg from substantial degradation in minimal essential media at physiological conditions over 9 days. The liberated Ga ions from the coatings upon Mg specimens inhibited the growth of bacterial tested. The Ga dopants showed minimal interferences with the SrPO4 based coating, which boosted osteoblasts and undermined osteoclasts in in vitro co-cultures model.The results evidenced this new material may be further translated to preclinical trial in large animal model and towards clinical trial.Acknowledgements: Authors are grateful to the financial support from the Australian Research Council through the Linkage Scheme (ARC LP150100343). The authors acknowledge the facilities, and the scientific and technical assistance of the RMIT University and John Curtin School of Medical Research, Australian National University.

Synthesis of a highly conductive coordination polymer film via a vapor-solid phase chemical conversion process.

A novel vapor-solid phase chemical conversion process is reported here to synthesise high-quality films of the conductive coordination polymer (c-CP) Ag5BHT (BHT = benzenehexanothiolate), which has the potential to be applied for the synthesis and processing of c-CP electronic devices. This approach involves reacting a silver oxide precursor and an H6BHT linker in an isopropanol solvent vapor atmosphere to obtain Ag5BHT thin films with controllable thickness (100-300 nm). The as-synthesized Ag5BHT thin films exhibit conductivities as high as 10 S cm-1. Additionally, under field-effect modulation, these nanofilms demonstrate remarkably high charge mobility (38 cm2 v-1 s-1).

Investigating the Influence of Pre-Grown Copper Oxide Film on Sulfide-Induced Corrosion of Copper

Used nuclear fuel should be confined safely and permanently due to its detrimental effect on human health and the environment. The universally proposed plan for the permanent disposal of used nuclear fuels is to bury the containers containing the nuclear used fuels in a multi-barrier system known as a deep geological repository (DGR) at a depth 500 m underground. The container is the key engineered barrier that can withstand long-term mechanical loads and the corrosive environment. The proposed container in some countries will be designed with either a cylindrical Cu shell containing a nodular cast iron insert (Sweden, Finland) or a Cu‐coated carbon steel vessel (Canada). After emplacement, the container will experience a range of conditions underground, evolving from warm, humid, and oxidizing to cool, dry, and anoxic over time.During the initial oxidizing period, the entrained oxygen, trapped in the DGR upon sealing, and the water-radiolysis will lead to the formation of an oxide/hydroxide film on the Cu container surface. Once anoxic conditions are eventually established, sulfide ions produced by the action of sulfate-reducing bacteria remote from the container will become the main potential oxidant.So far, considerable efforts have been devoted to investigating exclusively either the oxic period or the anoxic period. However, the significant gap that the current research aims to address is how the early period of oxide growth affects the later stages of the repository evolution, at which time the primary threat to the integrity of the Cu container would be sulfide ions within the groundwaters. In this series of experiments, various methods were applied to create different types of copper oxide/hydroxide layers with known compositions and unique structures, to investigate their role in the subsequent sulfide-induced corrosion of the underlying Cu under de-aerated conditions. The morphology of the surface oxide film and the nature and concentration of sulfide species will influence the possible manners in which the sulfide species could interact with the oxide film; for example: Chemical conversion of copper oxide to copper sulfideGalvanically-coupled processes between the copper oxide reduction and Cu oxidation by sulfideDirect corrosion of Cu by sulfide species arriving at the metal surface Our results have shown that regardless of the composition and nature of the oxide film, either a single-phase oxide film or a dual layer of combined copper oxides, the pre-grown oxide film on the Cu surface is partially converted to a copper sulfide film via chemical conversion and/or galvanically-coupled processes. Moreover, an unreacted remnant of the oxide layer was detected on the surface, surviving for longer than the duration of our experiments. This remnant oxide is non-protective, and permits direct corrosion of Cu by sulfide species arriving at the metal surface.Oxide films were grown either electrochemically, radiolytically, or chemically. The electrochemically-grown oxides, upon exposure to sulfide solutions, underwent quick conversion to copper sulfide (Cu2S) as shown by the corrosion potential (Ecorr) measurements and cathodic stripping voltammetry (CSV) at different immersion times. The same results were observed for the radiolytically-grown oxide with a multi-layer structure composed of Cu(I) and Cu(II) oxides. The thickness of the two mentioned oxides was on the nanometre scale.Chemically grown oxides were thicker than the electrochemically- and radiolytically-grown oxides. The results of CSVs showed that some parts of the oxide film and the sulfide film formed on top of the oxide film could not be cathodically stripped from the surface and remained in the form of a defective film, and that direct corrosion of Cu occurred, driven by sulfide species reaching the metal surface. This suggests that conversion of oxide to sulfide films is fastest when an electrochemical pathway is available, and much slower if it must depend on the chemical pathway. The regions of the oxide which were not connected electrically to the surface could only undergo chemical conversion. The results obtained from immersion of copper oxide powder in sulfide solution support the idea that the chemical conversion is not as quick as the electrochemical reaction in the presence of copper metal.

Photodriven Methane Conversion on Transition Metal Oxide Catalyst: Recent Progress and Prospects.

Methane as the main component in natural gas is a promising chemical raw material for synthesizing value-added chemicals, but its harsh chemical conversion process often causes severe energy and environment concerns. Photocatalysis provides an attractive path to active and convert methane into various products under mild conditions with clean and sustainable solar energy, although many challenges remain at present. In this review, recent advances in photocatalytic methane conversion are systematically summarized. As the basis of methane conversion, the activation of methane is first elucidated from the structural basis and activation path of methane molecules. The study is committed to categorizing and elucidating the research progress and the laws of the intricate methane conversion reactions according to the target products, including photocatalytic methane partial oxidation, reforming, coupling, combustion, and functionalization. Advanced photocatalytic reactor designs are also designed to enrich the options and reliability of photocatalytic methane conversion performance evaluation. The challenges and prospects of photocatalytic methane conversion are also discussed, which in turn offers guidelines for methane-conversion-related photocatalyst exploration, reaction mechanism investigation, and advanced photoreactor design.

Plasma‐Assisted CO2 Reduction into Nanocarbon in Water Using Sonochemically Dispersed Liquid Gallium

AbstractCarbon dioxide is a greenhouse gas that contributes to global warming but fortunately can be removed via chemical conversion processes that often involve a reduction step. Dielectric barrier discharge (DBD) plasma is an effective way to promote chemical reduction processes but requires a catalyst for energetically demanding reactions. In this study, the rapid conversion of CO2 into solid carbon via a DBD plasma is reported using dispersed liquid metal Ga which is first converted into GaOOH particles to ultimately form a GaOOH/C nanocomposite. Raman and X‐ray diffraction (XRD) experiments indicate that amorphous activated carbon is formed after the plasma treatment. Further analysis demonstrates that highly dispersed sub‐nano‐sized carbon particles containing oxygen functional groups are formed uniformly on the GaOOH surface. The CO2 conversion mechanism suggests that plasma electrons activate CO2 molecules, while plasma‐generated oxygen vacancies on the catalyst surface help dissociate CO2 into solid carbon. This work opens a new approach for synthesizing materials comprising of highly dispersed sub‐nano‐sized carbon on a metal oxide support suitable for other applications such as adsorption, heterogenous catalysis, and energy conversion.

Process simulation and reaction performance evaluation of CO2 chemical looping conversion based on modified bauxite residue oxygen carriers

A large number of greenhouse gas emissions have brought a series of environmental problems, so it is urgent to realize efficient conversion of CO2. The multistage regeneration process of CO2 chemical looping conversion was established and the process simulation analysis carried out with Aspen Plus. The system’s feasibility was verified by simulation and the process needed to provide additional energy input, and the sensitivity analysis of different operating conditions was carried out to provide guidance for subsequent experimental design. Oxygen carrier bauxite residue was modified by acid washing and CeO2 impregnation, and the reaction characteristics were evaluated via a fixed-bed reactor and on-line mass spectrometry, and the kinetic parameters of the reaction were solved by gas-solid reaction kinetics. The results showed that 12 wt% CeO2 loading oxygen carrier had the highest yield and average formation rate of CO, which were 6.22 mmol·g−1 and 388.71 μmol·g−1·min−1, respectively. The oxygen carrier conversion (oxygen vacancy utilization) was close to 100% after modification, while that of single bauxite residue oxygen carrier was only 60%. The reaction system conformed to the first-order reaction model, and the activation energy was 33.90 kJ·mol−1. This study provided new insight into chemical looping conversion of CO2.