Selectivity Of C2 Hydrocarbons Research Articles

Synergetic effect of iron and tungsten on molybdenum‐doped HZSM‐5 zeolite in catalytic methane dehydroaromatization

AbstractMethane dehydroaromatization is a viable route for production of carbon and valuable petrochemicals. Unlike Fischer–Tropsch and methanol synthesis processes which have been scaled up to commercial level, development of methane dehydroaromatization to commercial level has been hampered by various challenges. In this work, a 5.4 wt. % trimetallic (Fe‐W‐Mo/HZSM‐5) catalyst has been synthesized, characterized, and applied in catalytic methane dehydroaromatization reaction. A gas chromatograph was used to analyze both liquid and gaseous products from the reactor. Based on 0.0013 moles of reacted methane after 240 min time on stream at 750, GHSV 960 mlg‐1cath‐1, and atmospheric pressure, a 5.4% Mo/HZSM‐5 catalyst recorded 7.9% methane conversion, 10.6% C2 hydrocarbon selectivity, 51.8% benzene selectivity, 9.8% toluene selectivity and 27.8% coke selectivity. Doping Mo/HZSM‐5 with Fe reduced methane conversion by 4.0%, increased C2 hydrocarbon selectivity by 1.7%, reduced benzene selectivity by 6.2% and increased toluene and coke selectivity by 1.8% and 2.8% respectively. Doping Mo/HZSM‐5 with W increased methane conversion by 7.3%, reduced C2 hydrocarbon selectivity by 2.1%, reduced benzene selectivity by 7.6% and increased toluene and coke selectivity by 0.3% and 9.4% respectively. When iron and tungsten were loaded onto Mo/HZSM‐5, catalytic activity of the tri‐metallic catalyst in methane conversion reduced by 2.0%, C2 hydrocarbon selectivity increased by 2.7%, benzene selectivity reduced by 3.1%, toluene selectivity reduced by 3.7%, and coke selectivity increased by 4.1%. Therefore, this present work demonstrates that metal synergy in a tri‐metallic catalyst plays a role in methane conversion and selectivity towards useful hydrocarbons.

M/BiOCl-(M=Pt, Pd, and Au) Boosted Selective Photocatalytic CO2 Reduction to C2 Hydrocarbons via *CHO Intermediate Manipulation.

Selective CO2 photoreduction to C2 hydrocarbons is significant but limited by the inadequate adsorption strength of the reaction intermediates and low efficiency of proton transfer. Herein, an ameliorative *CO adsorption and H2O activation strategy is realized via decorating bismuth oxychloride (BiOCl) nanostructures with different metal (Pt, Pd, and Au) species. Experimental and theoretical calculation results reveal that distinct *CO binding energies and *H acquisition abilities of the metal cocatalysts mediate the CO2 reduction activity and hydrocarbon selectivity. The relatively moderate *CO adsorption and *H supply over Pd/BiOCl endows it with the lowest free energy to generate *CHO, leading to its highest activity of hydrocarbon production. Specifically, the Pt cocatalyst can efficiently participate in H2O dissociation to deliver more *H for facilitating the protonation of the *CHO and *CHOH, thereby favoring CH4 production with 76.51% selectivity. A lower *H supply over Pd/BiOCl and Au/BiOCl results in a large energy barrier for *CHO or *CHOH protonation and thus a more thermodynamically favored OC─CHO coupling pathway, which endows them with vastly increased C2 hydrocarbon selectivity of 81.21% and 92.81%, respectively. The understanding of efficient C2 hydrocarbon production in this study sheds light on how materials can be engineered for photocatalytic CO2 reduction.

Fundamentals of enhanced oxygen releasability of Mn-Na2WO4/SiO2 through cofed water for efficient oxidative coupling of methane in a chemical looping mode

The oxidative coupling of methane (OCM) to C2H6 and C2H4 (C2-hydrocarbons) is an industrially attractive reaction, which has not yet been commercialized. Apart from the low selectivity to C2-hydrocarbons at high degrees of CH4 conversion, another substantial drawback is the necessity to use pure O2 when this oxidant and methane are cofed. Original OCM studies used an approach called chemical looping OCM (CL-OCM) that consists of alternating feeding of methane and air for product formation and catalyst reoxidation, respectively. The developed catalysts, however, suffer from their low ability to provide lattice oxygen for the desired reaction. Herein, we demonstrate that this catalyst property can be significantly improved when performing CL-OCM over Mn-Na2WO4/SiO2 catalysts in the presence of water. In comparison to water-free CL-OCM, both methane conversion and C2-hydrocarbons selectivity increase resulting in at least doubling of the yield of these products. The selectivity to ethylene of about 53 % was obtained at about 24 % CH4 conversion. The total selectivity to C2-hydrocarbons was about 76 %. The analysis of selectivity-conversion relationships for C2H4, C2H6, CO and CO2 proved that water does not alter their general formation pathways but influences the kinetics of their formation.In situ X-ray diffraction, in situ UV–vis spectroscopic, and temperature-programmed tests (H2-TPR and O2-TPD with or without cofed H2O) showed that Mn2O3 acts as the oxygen carrier in CL-OCM. In-situ DRIFTS proved the presence of O2– and O22–. They can interact with water yielding OH radicals that accelerate CH4 conversion.

Effect of different oxygen species on the oxidative coupling of methane over TiO2 catalysts

TiO2 is widely used in oxidative coupling of methane (OCM) reaction because of its low cost, reducibility and nontoxicity, but pure TiO2 has poor activity on methane activation. Density functional theory with an additional Hubbard-like parameter (DFT + U) was used to research OCM reaction on Ir/TiO2(001), Pt/TiO2(001) and Mn/TiO2(001) catalysts to explore catalysts with high activity and C2 hydrocarbon selectivity. The results indicate that Ir, Pt and Mn doping can significantly improve the activity of lattice oxygen and reduce the activation energy of methane dissociation. Additionally, the evolution of oxygen species on Ir/TiO2(001) Pt/TiO2(001) and Mn/TiO2(001) catalysts show that the lattice oxygen species and peroxide species have the strongest activity to activate methane. However, the superoxide species has the worst activity. Furthermore, the formation paths of ethane and ethylene were researched on Ir/TiO2(001), Pt/TiO2(001) and Mn/TiO2(001) surfaces. And we expect that Ir/TiO2(001) is effective for catalyzing OCM reaction.

Dehydrogenation Coupling of Methane Using Catalyst-Loaded Proton-Conducting Perovskite Hollow Fiber Membranes.

Catalytic dehydrogenation coupling of methane (DCM) represents an effective way to convert natural gas to more useful C2 products (C2H6, C2H4). In this work, BaCe0.85Tb0.05Co0.1O3−δ (BCTCo) perovskite hollow fiber membranes were fabricated by the combined phase inversion and sintering method. SrCe0.95Yb0.05O3−δ (SCYb) perovskite oxide was loaded as a catalyst onto the inner hollow fiber membrane surface, which promoted the CH4 conversion and the C2 hydrocarbon selectivity during the DCM reaction. The introduction of steam into the methane feed gas mixture elevated the C2 selectivity and yield due to the alleviation of coke deposition. Switching N2 to air as the sweep gas further increased the C2 selectivity and yield. However, the conversion of methane was limited by both the low permeability of the membrane and the insufficient catalytic activity of the catalyst, leading to low C2 yield.

Nonoxidative Coupling of Methane over Ceria-Supported Single-Atom Pt Catalysts in DBD Plasma.

Plasma-catalytic direct nonoxidative coupling of methane (NCM) into C2 hydrocarbons was investigated over ceria-supported atomically dispersed Pt (Pt/CeO2-SAC) and nanoparticle Pt (Pt/CeO2-NP) catalysts in dielectric barrier discharge (DBD) plasma. Nonthermal plasma facilitated C-H bond dissociation in CH4 at low temperatures (<150 °C) and atmospheric pressure. The presence of Pt/CeO2 catalysts in plasma further enhanced CH4 conversion and C2 hydrocarbon selectivity by enabling the conversion of vibrationally excited methane species with high internal energy on active Pt sites. Noticeably, the Pt/CeO2-SAC catalyst displayed a more remarkable performance, with a CH4 conversion of 39% and a C2 selectivity of 54% at 54 W. The enhanced CH4 conversion was attributed to abundant coordinatively unsaturated Pt sites in Pt/CeO2-SAC, which were more active for C-H bond scission. Meanwhile, isolated Pt atoms in Pt/CeO2-SAC promoted C2 hydrocarbon formation by hindering the unselective formation of coke from deep dehydrogenation of CHx• intermediates and higher hydrocarbons from oligomerization reactions.

Oxidative coupling of methane over Mo-Sn catalysts.

A novel Mo-Sn catalyst for the oxidative coupling of methane was designed using a hydrothermal method. At 650 °C, the conversion of methane was 8.6% and the selectivity of the C2 hydrocarbons reached as high as 98.1% over the Mo1Sn3 catalyst, with a CO2 selectivity of only 0.8%. We demonstrated that the deep oxidation of methane to CO2 was further inhibited due to the synergistic effects of moderately strong basic sites and reactive oxygen species on the catalyst surface.

Radial Basis Function Neural Network Model Prediction of Thermo-catalytic Carbon Dioxide Oxidative Coupling of Methane to C2-hydrocarbon

Various anthropogenic activities often result in the emission of carbon dioxide (CO2), which is one of the principal components of greenhouse gases responsible for greenhouse effect. One vital strategy to mitigate the effect of the released CO2 on the environment is through sustainable utilization and conversion to value-added chemicals. This study employs the Radial Basis Function artificial neural network for modeling the prediction of thermo-catalytic CO2 oxidative coupling of methane to C2-hydrocarbons. The various architecture of the Radial Basis Function ANN was developed, trained, and tested using the non-linear relationship between the input parameters (reaction temperature, amount of CaO and MnO in the CaO-MnO/CeO2 catalysts and the CO2/CH4 ratio) and the output parameters (C2 hydrocarbon selectivity and yield). The Radial Basis Function ANN architecture with the topology of 4-20-2, representing the input layer, hidden neurons, and the output layer offers the best performance with a sum of square error (SSE) of 3.9 × 10−24 for training and 0.224 for testing. The R2 of 0.989 and 0.998 obtained for the prediction of the selectivity and the yield of the C2 hydrocarbon is an indication of the robustness of the Radial Basis Function ANN model. The sensitivity analysis revealed that the input parameters significantly influence the model output. However, the reaction temperature has the most significant influence on the model output based on the level of importance.

Dendritic copper microstructured electrodeposits for efficient and selective electrochemical reduction of carbon dioxide into C1 and C2 hydrocarbons

Here, we report synthesis of copper microstructures-based electro-catalyst with controlled morphologies and crystallinity via a rudimentary simple and green electrochemical dissolution method. The variations in the growth pattern of the dendritic shaped Cu microstructures were studied to understand the evolution of Cu dendrites with respect to several electrolysis parameters viz. applied bias voltage, concentration of organic additives, i.e. L-ascorbic acid, and electrolysis time and temperature. We show that these microstructures demonstrate efficient and selective electrochemical conversion of CO2 into CO along with methane and ethane from CO2-saturated moistened di-methyl sulfoxide (DMSO) electrolyte solution. Our results establish that the selectivity for C1 or C2 hydrocarbons (methane or ethane) as a major product can be tuned systematically by altering the extent of branching in dendrite microstructures as well as the extent of exposure of (111) and (200) facets. The production of C1 and C2 hydrocarbons along with CO in the present study can be ascribed to the availability of protons from the residual water (<0.2 % v/v or ca. 1000 ppm) in hygroscopic DMSO. The optimized dendritic shaped electro-catalyst is perceived to have the fine branching and exposed facets that convert CO2 into CO with Faradaic Efficiency (F.E.) of 32 %, ethane with F.E. of 29 % and methane with F.E. of 5%. The production of ethane reaches a maximum of 33 % at -1.5 V (NHE), which to the best of our knowledge is the highest reported so far for electroreduction of CO2 over Cu in organic media.

Building a robust 3D Ca-MOF by a new square Ca4O SBU for purification of natural gas.

For the first time, a new square Ca4O SBU is introduced into a 3D Ca-MOF, ([MeNH2]2[Ca4O(MTB)2(EtOH)4])·(solvent)n (1), to generate a (4,8)-connected flu-topology structure. Compound 1 exhibits selective adsorption of C3 and C2 hydrocarbons and CO2 over CH4 with especially high IAST selectivities for C3 hydrocarbons over CH4 (at 15/85 and 50/50 ratio) at 298K and 1 bar.

Preparation of LaAlO3 perovskite catalysts by simple solid-state method for oxidative coupling of methane

Abstract The preparation of LaAlO3 perovskite catalysts for the oxidative coupling of methane (OCM) using a very simple solid-state method with good reproducibility is described. To obtain high performance LaAlO3 catalysts, preparation conditions such as time, temperature, and oxygen content, which have a strong effect on the catalytic activity, are controlled during the calcination process. As the calcination time and temperature increase, the catalytic activity of LaAlO3 improves due to the good homogeneity and high crystallinity of LaAlO3 perovskite. Especially, the LaAlO3 catalyst calcined at 1350 °C for 24 h shows the highest selectivity and yield of C2 hydrocarbons. LaAlO3 catalysts calcined at various oxygen fractions show a volcano-shaped curve with respect to oxygen content in calcination gas, and the LaAlO3 catalyst prepared with an oxygen content of 5 % exhibits the best catalytic performance in this reaction. The appropriate oxygen fraction provides the LaAlO3 catalyst with a large amount of electrophilic lattice oxygen species and a sufficient amount of adsorption oxygen species, which are known to play key roles in the OCM reaction. This study clearly reveals this simple, highly reproducible, and mass-productive solid-state method as a promising preparation method for high performance LaAlO3 perovskite catalysts for OCM.

Study on CH4 dry reforming process by high power inductively coupled plasma torch at atmospheric pressure

CO2 dissociation and CH4 dry reforming, by high power inductively coupled plasma (ICP) torch at atmospheric pressure, have been studied. At a frequency of 400 kHz and power of 30 kW, the ICP torch source dissociates CO2 gas directly, causing CH4 dry reforming. The resulting products are composed of syngas, C2H6, C2H4, and C2H2. The results show conversion efficiencies (CE) for both CO2 and CH4 of 95%. At an input power of 22 kW, a CO2 flow rate of 30 SLM, and a CH4 flow rate of 36 SLM, the energy conversion efficiency (ECE) is 57%. As input CH4 flow rate increases, the selectivity of CO and H2 decreases and that of C2 hydrocarbons increases. In this condition, ECE increases. As a result, the high CE of CO2 and CH4, the large amount of products, and the high selectivity of C2 hydrocarbons can be seen as important factors for achieving higher energy conversion efficiency in the CH4 dry reforming process. The associated chemical reactions are simulated using CHEMKIN-PRO tool, and the results illustrate the tendency of CE to vary with variations in selected parameters, and syngas and C2 hydrocarbons production trends achieved in the simulation agree with experimental results.

Tuning the C2/C1 Hydrocarbon Separation Performance in a BioMOF by Surface Functionalization

Solvothermal reaction of adenine, 1,3,6,8‐tetrakis(p‐benzoic acid)pyrene (H4TBAPy), and Zn(NO3)2 in DMF afforded a three‐dimensional anionic bioMOF 1. It features one‐dimensional tubular channels with exposed Watson–Crick faces and nitrogen‐rich purines, which endows 1 with multiple adsorption sites on its polar surface, translating into high selectivity of C2 hydrocarbons over C1. Moreover, an isostructural bioMOF 1‐NH2 was synthesized by using 2‐aminoadenine in place of adenine, resulting in additional amine groups pointing toward the channel cavity. The added strong adsorption sites have been demonstrated to be able to further increase the selectivity of C2 hydrocarbons over C1.

Multifunctional macroporous solid oxide fuel cell anode with active nanosized ceramic electrocatalyst

In this work, an alternative anode material, consisting of perovskite-type manganese-doped lanthanum aluminate (La1.5Al0.33Mn0.17O3), was proposed and implemented. The solid oxide fuel cell anode was produced by the wet impregnation of nanoparticles into a macroporous electrolyte-based scaffold material. The produced cell was characterized by X-ray diffraction and scanning electron microscopy, from which the morphology of the scaffold, the particle size distribution, and porosity were extensively performed and discussed. Electrochemical and electrocatalytic tests were accounted by recording i-V plots with hydrogen or methane as fuels, and by measuring methane conversion rates and C2 hydrocarbons selectivity.The particle size distribution was confirmed to be submicrometric with the presence of nanoparticles. High levels of porosity (30–35%) were achieved at the scaffold and the cells were able to operate with hydrogen and methane as fuels delivering a power density of around 150 mW.cm−2 and yielding 30–70% C2 hydrocarbons selectivity, depending on operational conditions.

The non-catalytic partial oxidation of methane in a flow tube reactor using indirect induction heating – An experimental and kinetic modelling study

Methane partial oxidation is one way of producing synthesis gas which is the feedstock of Fischer-Tropsch synthesis and methanol synthesis. The high ignition temperature of methane partial oxidation is always a concern to industries and researches, leading to inaccuracies in temperature measurement, reaction model development, and subsequent understanding of reaction mechanisms and the predictive abilities of developed models. A gas-flow reactor system incorporating indirect induction heating was designed and operated for the non-catalytic partial oxidation of CH4. Experiments of methane partial oxidation diluted by nitrogen were conducted and the effects of temperature (1270–1767 K), stoichiometry (CH4/O2 = 1–2), and H2 addition were studied. Thermodynamic and kinetic simulations were also performed in this study and compared to the experimental results. Reduced mechanisms were applied in computational fluid dynamics (CFD) simulations to correct the temperature profiles which were adopted in kinetic modelling. Kinetic simulations of the experimental conditions were conducted using reported mechanisms: GRI-Mech 3.0 and the mechanism developed by Glarborg’s group. In general the simulated gas-phase compositions at the exit of the reactor and trends for each set of experiments were consistent with the experimental data. The Glarborg mechanism was found to be more accurate in the prediction of the selectivity of C2 hydrocarbons (particularly acetylene) as the Glarborg mechanism contains more pathways for the conversion of C2H2 into polycyclic aromatic hydrocarbons (PAHs). The combination of CFD modelling and kinetic modelling offset the deviation of temperature measurement and hence provided a sample for high temperature reaction simulation.

Non‐Oxidative Methane Conversion Using Lead‐ and Iron‐Modified Albite Catalysts in Fixed‐Bed Reactor

AbstractRaw and modified albite catalysts, including Pb/Albite and Fe/Albite catalysts, have been investigated for methane conversion to C2 hydrocarbons under non‐oxidative conditions. Introduction of Pb to albite improved the activity and selectivity to non‐coke products. Based on characterization, it was found that Pb entered into the alkali and alkaline‐earth metal sites of albite, while partial Fe doped in the tetrahedron sites and the other loaded on the surface of albite. At the reaction temperature of 1073 K, methane gas hourly space velocity (GHSV) of 2 L·gcat–1·h–1, catalyst dosage of 0.25 g (300 mesh), the methane conversion catalyzed by raw albite in the fixed‐bed micro reactor exhibited a methane conversion of 3.32%. Notably, introducing a Pb content of 3.4 wt% into albite greatly enhanced the conversion of methane up to 8.19%, and the selectivity of C2 hydrocarbons reached 99% without any coke under the same reaction conditions. While Fe‐doping could weakly heighten the methane conversion to 3.97%, and coke was formed. Thus, a comparison of Pb/Albite and Fe/Albite catalysts demonstrates that the catalytic activity of albite is mainly decided by alkali and alkaline‐earth metal sites, and lead‐modification can effectively improve the catalytic activity of albite.

Dry reforming of CO2[sbnd]CH4 assisted by high-frequency AC gliding arc discharge: Electrical characteristics and the effects of different parameters

In this work, a knife-shaped gliding arc discharge (GAD) reactor driven by high frequency AC (HFAC) power was employed to convert CO2 and CH4. The HFAC GAD exhibited good performance in dry reformation of CO2CH4. The development process with the HFAC GAD at a low gas flow rate was recorded and it is discussed with U-I waveforms and discharge images. The effects of input voltage, total gas flow rate, minimum electrode gap distance, and electrode thickness were investigated in terms of the CO2CH4 conversion rate, selectivity of CO, H2, and C2 hydrocarbons, specific energy density, and energy efficiency. The energy efficiency ranged from 1.58 to 2.21 mmol/kJ under changing operating conditions. The best conversions of CO2 and CH4 were achieved as 52.32% and 58.85%, respectively, with an energy efficiency of 1.65 mmol/kJ.

First-principles study of structure sensitivity of chain growth and selectivity in Fischer–Tropsch synthesis using HCP cobalt catalysts

Co (0001) prefers the CO insertion mechanism with high methane selectivity, but Co (101̄1) prefers the carbide mechanism with high C2-hydrocarbon selectivity.

Promotional Effects of In on Non-Oxidative Methane Transformation Over Mo-ZSM-5

We present a new class of catalysts, InMo-ZSM-5, which can be prepared by indium impregnation of Mo-ZSM-5. The incorporation of indium dramatically decreases coke formation during methane dehydroaromatization. The benzene and C2 hydrocarbons selectivity among total hydrocarbons over InMo-ZSM-5 remains comparable to that of Mo-ZSM-5 despite reduced methane conversion due to decreased coke formation. We found 1 wt% indium to be optimal loading for reducing coke selectivity to half that of Mo-ZSM-5. Characterization methods were not helpful in discerning the interaction of In with Mo but experiments with bimetallic 1In2Mo-ZSM-5 and mechanical mixture 1In+2Mo-ZSM-5 suggest that In and Mo need to be in close proximity to suppress coke formation. This is supported by temperature programmed reduction experiments which show that In incorporation leads to lower Mo reduction temperature in In2Mo-ZMS-5.

Facet-Controlled CeO2 Nanocrystals for Oxidative Coupling of Methane.

Whether the catalysts of the high temperature reaction such methane oxidation coupling has a structure-sensitive catalytic behavior or not, it is discussed and confirmed the shape-specific impact on methane activity by designing the catalysts with different crystal facets exposed. CeO2 nanowires enclosed by {110} and {100} planes show the higher CH4 conversion and higher C2 hydrocarbons (C2H4 and C2H6) selectivity, compared with particle CeO2 rounded by {111} and {100} planes, suggesting that CeO2 (110) surface favors the activation of CH4. Encouraged by the result, to control facet-controlled synthesis of catalysts for tailoring the catalytic properties at high temperature, the CeO2 (110) surface is chosen as doped sites to form the doped catalyst such as Ca doped CeO2 nanowires for OCM reaction, enhancing C2 hydrocarbons selectivity dramatically and suppressing the deep oxidation product (CO and CO2) selectivity.