Production of acetylene by a microwave catalytic reaction of water and carbon

The feasibility of producing hydrocarbons in a microwave induced catalytic reaction of carbon and water was successfully demonstrated. The major reaction products are acetylene, methane, ethylene and ethane. Other significant products include propylene, propyne, cyclopropane, carbon dioxide and carbon monoxide. Relative product yields and their distribution depend on a number of experimental variables, such as irradiation time, incident microwave power, water/carbon ratio and the characteristics of the microwave pulse train. At short irradiation times and low incident power only C₁ — C₂ products were observed, their rates of formation being an exponential function of the incident microwave power. High incident power led to the formation of C₃ to C₆ hydrocarbons at the expense of acetylene. Initial addition of methane and carbon dioxide to the reaction mixture increased the yield of acetylene, whereas addition of methanol to water resulted in a sharp increase in the amounts of both methane and acetylene. Mechanisms are considered to account for these observations.     

Mechanism of phthalic anhydride formation in the oxidation of n-pentane on a vanadium-phosphorus oxide catalyst

The reaction paths of product formation in the partial oxidation of n-pentane on vanadium-phosphorus oxide (VPO) and VPO-Bi catalysts are considered. The condensed products of n-pentane oxidation were analyzed by chromatography-mass spectrometry, and the presence of C₄ rather than C₅ unsaturated hydrocarbons was detected. It was found that the concentration of phthalic anhydride in the products increased upon the addition of C₄ olefins and butadiene to the n-pentane-air reaction mixture. With the use of a system with two in-series reactors, it was found that the addition of butadiene to a flow of n-butane oxidation products (maleic anhydride, CO, and CO₂) resulted in the formation of phthalic anhydride. The oxidation of 1-butanol was studied, and butene and butadiene were found to be the primary products of reaction; at a higher temperature, maleic anhydride and then phthalic anhydride were formed. The experimental results supported the reaction scheme according to which the activation of n-pentane occurred with the elimination of a methyl group and the formation of C₄ unsaturated hydrocarbons. The oxidation of these latter led to the formation of maleic anhydride. The Diels-Alder reaction between maleic anhydride and C₄ unsaturated hydrocarbons is the main path of phthalic anhydride formation.     

Formation of C1–C5 Hydrocarbons from CCl4 in the Presence of Carbon-Supported Palladium Catalysts

Along with hydrodechlorination, the formation of C₁ and higher hydrocarbons takes place in a flow system in the presence of catalysts containing 0.5–5.0% Pd supported on a Sibunit carbon carrier at 150–230°C. In the entire range of conditions examined, the reaction products are primarily methane, C₂–C₄ hydrocarbon fractions, and C₅ traces. The catalysts are stable in operation, and a high conversion of CCl₄ was retained for a long time interval. The nonselective formation of linear and branched hydrocarbons is indicative of a radical mechanism of the process.     

复合催化剂上CO2加氢合成C2烃类

介绍了由CO₂+H₂合成C2⁺烃的几种复合催化剂体系的研究进展，比较和评价了复合催化剂体系的活性和选择性及对C2⁺烃类生成的影响。着重于复合催化剂体系对C4⁺烃的生成及产物分布的影响并简述反应机理。     

Methane conversion by various metal, metal oxide and metal carbide catalysts

The progress in the field of methane conversion into higher hydrocarbons including aromatics and oxygenated compounds in the recent five years will be reviewed shortly, together with a new type of the methane conversion reaction with carbon monoxide at lower temperatures (600–700 K) by supported group VIII metal catalysts. Benzene was formed selectively among hydrocarbons in the CH₄–CO reaction over silica-supported Rh, Ru, Pd and Os catalysts under atmospheric pressure. Both CH₄ and CO were required for benzene formation, and only ethane and ethylene were formed besides benzene. The amount of C₃–C₅ hydrocarbons was negligible, which suggests that a completely different mechanism from the CO–H₂ reaction may be operating over these catalysts despite of the similarity in the reaction conditions with the CO–H₂ reaction. The mechanism of benzene formation was studied deeply by means of kinetical investigation as well as infrared spectroscopy and isotopic tracer method in connection with that of CO hydrogenation.     

Influence of Helium on the Conversion of Methane and Carbon dioxide in a Dielectric Barrier Discharge

We have studied the production of synthesis gas and other hydrocarbons in a dielectric barrier discharge using mixtures of helium, methane and carbon dioxide. It was found that helium has a significant influence on the discharge, decreasing the breakdown voltage and increasing the rate of conversion of CH₄ and CO₂. However it also decreases the selectivities and the range of stable operating conditions for the discharge. The main products obtained were H₂, CO, C₂H₆ and C₃H₈ but traces of other hydrocarbon, carbon deposition and the formation of condensable products were also detected. The rate of conversion and conversion abilities were obtained by fitting the conversion results to a model.     

Electrochemical CO2 reduction reaction on cost-effective oxide-derived copper and transition metal–nitrogen–carbon catalysts

The electrochemical CO₂ reduction reaction (CO₂RR) either to generate multicarbon (C₂₊) or single carbon (C₁) value-added products provides an effective and promising approach to mitigate the high CO₂ concentration in the atmosphere and promote energy storage. However, cost-effectiveness of catalytic materials limits practical application of this technology in the short term. Herein, we summarize and discuss recent and advanced works on cost-effective oxide-derived copper catalysts for the generation of C₂₊ products (hydrocarbons and alcohols) and transition metal–nitrogen–doped carbon electrocatalytic materials for C₁ compounds production from CO₂RR. We think they represent suitable electrocatalyst candidates for scaling up electrochemical CO₂ conversion. This short review may provide inspiration for the future design and development of innovative active, cost-effective, selective and stable electrocatalysts with improved properties for either the production of C₂₊ (alcohols, hydrocarbons) or carbon monoxide from CO₂RR.     

Synthesis and some aspects of the formation mechanism of carbon structures under hydrothermal conditions

The formation of carbon structures upon the reactions of organic compounds with strong mineral acids under hydrothermal conditions was studied. The reactions were found to give amorphous carbon, microcrystalline graphite, nanodiamonds, diamond-like carbon, diamonds, C₆₀ and C₇₀ fullerenes, and carbolite. Hydrocarbons of various compositions including aromatics and naphthenes were detected among the reaction products. A possible mechanism of the formation of carbon structures with sp ² bond hybridization under hydrothermal conditions was proposed.     

Catalytic efficiency of some novel nanostructured heterogeneous solid catalysts in pyrolysis of HDPE

In the present study, the catalytic conversion of high density polyethylene (HDPE) to useful products has been investigated in the presence of BaTiO₃ based catalysts in a micro steel reactor at 350 °C and 30 min reaction time. The catalysts, including BaTiO₃, Pb/BaTiO₃, Co/BaTiO₃ and Pb–Co/BaTiO₃ were prepared in the laboratory by reactive calcination method and characterized by Scanning Electron Microscopy (SEM), Energy Dispersive X-rays (EDX), Surface Area Analyzer (SAA) and X-rays Diffractometry (XRD). The product yields (over all yields and yields of liquid, gas and coke/residue) as a function of individual catalyst concentration was studied. The result indicated a promising effect of the catalysts used on conversion to liquid products and their composition in term of carbon range (C₆ – >C₃₀) & hydrocarbon group types (paraffin's, olefins, naphthenics, and aromatics). Among the catalysts used, Pb–Co/BaTiO₃ gave the maximum yield of liquid products (86%) when used in 1 wt % loading. The same catalyst gave the average yield (20–25%) of different range hydrocarbons i.e. C₆–C₁₂, C₁₃–C₁₆, C₁₇–C₂₀ and C₂₀–C₃₀. Inversely, the un-doped BaTiO_3, favored the formation of C₆–C₁₂ and C₁₃–C₁₆ range hydrocarbons, whereas Pb doped BaTiO₃ and Co doped BaTiO₃ enhanced the yield of C₁₃–C₁₆, and C₂₀–C₃₀ range hydrocarbons. Regarding the hydrocarbon group types, all catalysts significantly increased the formation of paraffins and reduced olefins and naphthenes.     

Co0−Coδ+ Interface Double-Site-Mediated C−C Coupling for the Photothermal Conversion of CO2 into Light Olefins

Solar-driven CO₂ hydrogenation into multi-carbon products is a highly desirable, but challenging reaction. The bottleneck of this reaction lies in the C−C coupling of C₁ intermediates. Herein, we construct the C−C coupling centre for C₁ intermediates via the in situ formation of Co⁰−Co^δ+ interface double sites on MgAl₂O₄ (Co−CoO_x/MAO). Our experimental and theoretical prediction results confirmed the effective adsorption and activation of CO₂ by the Co⁰ site to produce C₁ intermediates, while the introduction of the electron-deficient state of Co^δ+ can effectively reduce the energy barrier of the key CHCH* intermediates. Consequently, Co−CoO_x/MAO exhibited a high C_2–4 hydrocarbons production rate of 1303 μmol g⁻¹ h⁻¹; the total organic carbon selectivity of C_2–4 hydrocarbons is 62.5 % under light irradiation with a high ratio (≈11) of olefin to paraffin. This study provides a new approach toward the design of photocatalysts used for CO₂ conversion into C₂₊ products.     

Composition of aromatic products in the catalytic degradation of the mixture of waste polystyrene and high-density polyethylene using spent FCC catalyst

In this chemical recycling process, spent FCC catalyst used had an advantage with an economical and environment aspect, such as a low catalyst price in liquid-phase reaction and a reuse of waste catalyst. The characteristics of oil product and its aromatic product distribution, as a function of reaction time in the reactor and also proportion of HDPE and PS in the mixture, were compared. Main products obtained were light hydrocarbons within the gasoline range that were mainly produced during initial reaction time. The formation of aromatic products such as styrene and ethylbenzene as major components depended appreciably on the reaction time, as well as the composition of HDPE and PS in the mixture used for degradation. For the distribution of C₉-C₁₂ alkylaromatic components as by-products, methylstyrene (C₁-styrene) and isopropylbenzene (C₃-benzene) components were the main products formed by β-scission and hydrogen transfer of PS, while the rest of alkylaromatic products showed very low fraction being 1% or less.     

Vapor—solid equilibrium for the CHONi system

The equilibrium states of the CHONi system are defined in relation to H₂CO compositions for temperatures ranging from 300 to 700 K and at atmospheric pressure.The gaseous species, H₂, H₂O, CO, CH₄…C₈H₁₈, C₂H₄… C₄H₈ are taken into account to determine the gas phase compositions imposed by the different equilibria between condensed phases (〈C〉, 〈Ni〉, 〈NiO〉, 〈Ni₃C〉, 〈Ni,C〉 solution).We have particularly investigated the values of chemical potential of carbon in the gas phases, fixed by equilibria between solid phases involving carbon, at which hydrocarbons higher than CH₄ appear. The method for determining the standard free enthalpy of formation of Ni₃C is discussed.     

Plasma-Chemical Conversion of Hydrogen Sulfide in the Atmosphere of Methane with Addition of CO<Subscript>2</Subscript> and O<Subscript>2</Subscript>

Plasma-chemical conversion of hydrogen sulfide in the atmosphere of methane with addition of CO₂ and O₂ in the nonequilibrium plasma of barrier discharge is studied. The degree of hydrogen sulfide removal reaches 97 vol%. The degree of methane transformation does not exceed 14 vol%. Gaseous reaction products contain hydrogen, carbon oxides, and C₂–C₄ hydrocarbons. The energy consumption for the removal of hydrogen sulfide ranges from 84 to 182 eV molecule^?1. The process is accompanied by the formation of deposits on the surface of reactor electrodes. The composition of deposits is studied. Organic linear and cyclic polysulfides, as well as sulfones of various structures are identified in soluble components of deposits. Based on the experimental data and the results of theoretical estimates, a radical chain reaction mechanism is proposed. It is shown that the formation of polysulfide compounds with terminal alkyl and oxygen-containing groups is provided by the reactions between atomic oxygen, SH, and alkyl radical which were formed in the initial stages of processes in the non-equilibrium plasma of barrier discharge.     

HDPE chemical recycling promoted by phenol solvent

The thermal cracking of HDPE in the presence of different amounts of phenol has been studied and compared with the reaction carried out without this solvent. HDPE conversion is enhanced with the amount of solvent, reaching a value of nearly 100% using a 1/10 HDPE/phenol ratio. The yield of the gaseous hydrocarbons also rose with the amount of phenol, olefins being the main products in this fraction. In all reactions, the main products of the C₅–C₃₂ fraction were linear hydrocarbons such as n-paraffins and α-olefins. The yields of both hydrocarbons increased in line with the amount of phenol. However, the increase was more significant in the case of α-olefins. All these results indicate that the phenol promotes the plastic degradation, enhancing the HDPE conversion and facilitating the formation of specific products. A reaction mechanism is proposed to explain these results, indicating random scissions and chain reactions which are favoured by the presence of this solvent during the HDPE thermal degradation.     

Time-resolved mass spectrometric study of the reaction H + Trans-2-Butene

The title reaction was studied in a discharge flow system using mass flow and modulated molecular beam sampling with phase-sensitive detection in order to obtain time-resolved mass spectrometric analysis. At total conversion exceeding 30%, the major products are methane and ethane when initially hydrogen atoms are in excess; when butene is in excess, the major products are ethane and propylene. No hydrocarbons with more than 4 carbon atoms were detected in the products. The reaction is a complicated one since the simplest reaction scheme that successfully simulates the experimental results comprises 20 elementary reactions. The simulation, coupled with sensitivity analysis, shows that with hydrogen atoms in excess, significant amounts of propylene formed in the initial decomposition of the butyl radical react further with hydrogen atoms to form methane and ethane. When butene is in excess, approximately [C₃H₆] ≈ [CH₄] + ½[C₂H₆] which means that this propylene does not react further and almost all methyl radicals end up as CH₄ or C₂H₆. At small conversion, simulation shows that the major product by far is propylene regardless of the [H]/[butene] ratio. The absence of higher hydrocarbons in the products is at variance with earlier results of Rabinovitch and coworkers; however the present work leads to a comparable value for the average rate constant ??_a = ωD/S where D and S is the amount of products arising from the decomposition and stabilization, respectively, of the butyl radical and ω is the collision frequency.     

New Fullerene-Based Stationary Phases for Gas Chromatography

Regularities were revealed for the retention of different classes of organic compounds on stationary phases based on C₆₀ and carbon nanotubes and on phases of mixed composition (C₆₀ and dibenzo-24-crown-8, C₆₀ and dibenzo-30-crown-10, and C₆₀ and -cyclodextrin) in gas chromatography. A synergistic effect was observed for the stationary phases of mixed composition. Quantitative estimation of the dispersion potential demonstrated that the C₆₀-based stationary phase differs significantly from hydrocarbon adsorbents and more closely resembles nonpolar liquid stationary phases. Under the conditions of solid-phase microextraction, an adsorbing element based on fullerene C₆₀ can be used for the preconcentration of aromatic hydrocarbons.     

A Free-Radical Prompted Barrierless Gas-Phase Synthesis of Pentacene

A representative, low-temperature gas-phase reaction mechanism synthesizing polyacenes via ring annulation exemplified by the formation of pentacene (C₂₂H₁₄) along with its benzo[a]tetracene isomer (C₂₂H₁₄) is unraveled by probing the elementary reaction of the 2-tetracenyl radical (C₁₈H₁₁^.) with vinylacetylene (C₄H₄). The pathway to pentacene—a prototype polyacene and a fundamental molecular building block in graphenes, fullerenes, and carbon nanotubes—is facilitated by a barrierless, vinylacetylene mediated gas-phase process thus disputing conventional hypotheses that synthesis of polycyclic aromatic hydrocarbons (PAHs) solely proceeds at elevated temperatures. This low-temperature pathway can launch isomer-selective routes to aromatic structures through submerged reaction barriers, resonantly stabilized free-radical intermediates, and methodical ring annulation in deep space eventually changing our perception about the chemistry of carbon in our universe.     

Pyrolysis and Oxidation of Methane in a RF Plasma Reactor

The chemical kinetic effects of RF plasma on the pyrolysis and oxidation of methane were studied experimentally and computationally in a laminar flow reactor at 100 Torr and 373 K with and without oxygen addition into He/CH₄ mixtures. The formation of excited species as well as intermediate species and products in the RF plasma reactor was measured with optical emission spectrometer and Gas Chromatography and the data were used to validate the kinetic model. The kinetic analysis was performed to understand the key reaction pathways. The experimental results showed that H₂, C₂ and C₃ hydrocarbon formation was the major pathways for plasma assisted pyrolysis of methane. In contrast, with oxygen addition, C₂ and C₃ formation dramatically decreased, and syngas (H₂ and CO) became the major products. The above results revealed oxygen addition significantly modified the chemistry of plasma assisted fuel pyrolysis in a RF discharge. Moreover, an increase of E/n was found to be more beneficial for the formation of higher hydrocarbons while a small amount of oxygen was presented in a He/CH₄ mixture. A reaction path flux analysis showed that in a RF plasma, the formation of active species such as CH₃, CH₂, CH, H, O and O (¹D) via the electron impact dissociation reactions played a critical role in the subsequent processes of radical chain propagating and products formation. The results showed that the electronically excitation, ionization, and dissociation processes as well as the products formation were selective and strongly dependent on the reduced electric field.     

Formation of carbon nanofilaments from C6-C16 alkanes over nickel-containing catalysts

The properties of 85%Ni/Al₂O₃ and NiO/Sibunit series catalysts have been studied in the formation of carbon nanofilaments from n-hexane, n-undecane, and n-hexadecane. In the temperature range 450–600°C, the reactivity of these hydrocarbons decreases in the following order: n-hexane > n-undecane > n-hexadecane. The deposition rate of carbon nanofilaments from n-hexane or n-undecane over the 85%Ni/Al₂O₃ catalyst in the range 450–600°C slightly depends on the reaction temperature. The activation energy of the formation of carbon nanofilaments from n-hexane is 10 kcal/mol and that from n-undecane, 13.5 kcal/mol. The rate-limiting reaction is the interaction of a paraffin molecule with the nickel metal surface. As the reaction temperature increases to 700°C, the formation rates of carbon nanofilaments from the C₆-C₁₆ paraffin hydrocarbons are equalized, which is associated with the increase in the intensity of thermal pyrolysis reactions of alkanes. The resulting olefins, first of all, ethylene and propylene, become major contributors to carbon formation.     

On-line gas chromatographic analysis of light Fischer-Tropsch synthesis products

Summary A simple gas chromatographic system has been developed for the rapid on-line analysis of light Fischer-Tropsch products. This involves a single chromatography fitted with two columns, a porous-layer open-tubular column coated with KCl deactivated alumina and a packed Porapak-Q column. The capillary column separates the 16 most common C₁−C₄ hydrocarbons and permits a reasonable analysis of the hydrocarbons in the C₅−C₇ range. The packed column is used for the separation of methane, carbon monoxide, carbon dioxide, water and methanol. Retention characteristics for the analysis on the capillary column are presented. The total analysis cycle is 30 minutes.