Production Of C2 Hydrocarbons Research Articles

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.

Bi4O5Br2 co-modified with oxygen vacancy and Bi metal for efficient photothermal conversion of CO2 to C2 hydrocarbons

Photothermal catalytic reduction of CO2 into high value-added C2 hydrocarbon products is a promising method for efficient CO2 conversion. However, current photocatalysts still encounter obstacles including limited photoabsorption range, rapid recombination of photogenerated carriers, and inadequate surface active sites. Herein, Bi4O5Br2 co-modified with oxygen vacancy (OV) and metal bismuth (Bi) (Bi4O5Br2-OV@Bi) has been prepared to optimize these crucial issues. Bi4O5Br2-OV@Bi delivers a remarkably improvement in CO2 photothermal conversion, reflecting by the notable increase in C1 (CO and CH4) and newly generated C2 (C2H4 and C2H6) products compared to pristine Bi4O5Br2. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) spectrometry reveals that OC−COH* intermediate promotes the C–C coupling for produce C2 hydrocarbons. This study strengthens the understanding of metal modification and defect engineering for forming C2 hydrocarbons on bismuth-based photocatalysts.

Reaction mechanism explorations on non-thermal plasma reforming of CO2-CH4 by combining kinetics modeling and emission spectroscopy measurements

Plasma-based dry reforming in an atmospheric dielectric barrier discharge (DBD) reactor has been thoroughly studied by combination of experiments and detailed kinetics simulation. With the assistances of in-situ optical emission spectroscopy (OES) measurements and reaction pathway analysis based on plasma kinetic simulation considering non-constant electric field and thermal effects, this study provided deep insights into the reaction mechanism of plasma-based dry reforming under varied feeding gas composition, gas residence time and operation temperature. A CH4 conversion as high as 44.76 % could be achieved without catalyst at 300 °C, with an SEI of 78 J/cm3 and feeding CH4 ratio of 50 %. Increase of feeding CH4 proportions were found to enhance the generation of C2 and C3 hydrocarbons. Consistently, the OES analysis showed that the relative intensities of spectra bands induced by deexcitation of CH, CO, and C2 also increased monotonically. With the same increment in SEI, increasing gas residence time led to larger promotions in CH4 and CO2 conversion, as being compared to increase of input power. The reason could be explained as that CH4 and CO2 molecules experienced more successive micro-discharges with a longer gas residence time, so more energy would be devoted into CH4/CO2 conversion, whereas more energy was dissipated into heat as rudely increased the discharge power due to the limit of reaction time. CO2 conversion continuously decreased with increasing gas temperature, owing to the recombination of CO and O enhanced at higher gas temperatures. Reaction pathway analysis showed that CH4 conversion was mainly induced by electronic dissociation and ionization at the discharge stage, while CO2 was mainly converted by recombination reaction CO2 + CH2 → CH2O + CO and also electron collision vibrational reaction e + CO2 → e + CO2(vn). The formation of C2 hydrocarbon products was supposed to follow the path of CH4 ↔ CH3/CH → C2H6 ↔ C2H5 ↔ C2H4 → C2H2.

Plasma-catalytic reforming of biogas into syngas over Ni-based bimetallic catalysts

Biogas reforming to syngas is an attractive route for the efficient utilization of biogas. In this work, plasma-catalytic dry reforming of biogas into value-added fuels and chemicals over Ni-based bimetallic catalysts was achieved using dielectric barrier discharge (DBD). The coupling DBD with 10Ni3Co exhibited the best reaction performance, reflected by the highest gas conversion, main gas product yield and selectivity, and fuel production efficiency (FPE). This hybrid process also favored the suppression of carbon deposition on the catalyst surface and the reduction of energy cost for both gas conversion and product formation. The maximum CO2 and CH4 conversion (29.8% and 49.1%) was obtained when the discharge power was 60 W, while a low discharge power (30 W) led to the highest FPE of 12.3%. By using Ni-based catalysts, we were able to tune the product distribution, favoring the generation of C3-C4 hydrocarbons and syngas while reducing the production of C2 hydrocarbons, with 10Ni3Co providing the most favorable results. Compared to other spent catalysts, the lowest carbon deposition (2.9%) was detected on the spent 10Ni3Co after 150 min of plasma reforming. Catalyst characterizations and density functional theory (DFT) calculations showed that the 10Ni3Co catalyst was superior due to a combination of factors such as a higher specific surface area, improved capability to adsorb CO2, strong interactions between the metals and the support, enhanced reducibility and the formation of a Ni-Co alloy. Furthermore, a simplified kinetics model was developed to better understand the effects of Ni-based bimetallic catalysts on the overall energy constant for the conversion of reactants in plasma-catalytic reforming of biogas.

Reduced TiO2 quantum dots/graphene for solar light driven CO2 reduction into precisely controlled C1 vs C2 hydrocarbon products without noble Co-catalyst

Photocatalytic CO2 reduction is a logical approach to overcome the energy crisis as well as to curb the anthropogenic CO2 emission by converting atmospheric CO2 with water vapour under irradiation into hydrocarbon fuels. Herein, for the first time, a noble metal-free photocatalyst comprised of reduced TiO2 quantum dots (TQDs) dispersed over graphene sheets has been successfully synthesized and employed for this reaction. EELS investigation reveals the addition of graphene has imparted oxygen vacancies inside TQDs, which in turn helps to enhance broad solar light absorption. TRPL spectroscopy revealed a prolonged charge separation in the heterostructure. Depending on graphene content, the ratio of the products has been changed; CH4:C2H6 from 3.41:1 to 1:1.62. The optimized sample exhibits 2.8- and 3.7-fold increment of CH4 and C2H6 yields compared to TQDs. Under the continuous mode, the photocatalyst has shown excellent stability of 72 h.

Mechanistic Insight into Hydrocarbon Synthesis via CO2 Hydrogenation on χ-Fe5C2 Catalysts.

Converting CO2 into value-added chemicals and fuels is one of the promising approaches to alleviate CO2 emissions, reduce the dependence on nonrenewable energy resources, and minimize the negative environmental effect of fossil fuels. This work used density functional theory (DFT) calculations combined with microkinetic modeling to provide fundamental insight into the mechanisms of CO2 hydrogenation to hydrocarbons over the iron carbide catalyst, with a focus on understanding the energetically favorable pathways and kinetic controlling factors for selective hydrocarbon production. The crystal orbital Hamiltonian population analysis demonstrated that the transition states associated with O-H bond formation steps within the path are less stable than those of C-H bond formation, accounting for the observed higher barriers in O-H bond formation from DFT. Energetically favorable pathways for CO2 hydrogenation to CH4 and C2H4 products were identified which go through an HCOO intermediate, while the CH* species was found to be the key C1 intermediate over χ-Fe5C2(510). The microkinetic modeling results showed that the relative selectivity to CH4 is higher than C2H4 in CO2 hydrogenation, but the trend is opposite under CO hydrogenation conditions. The major impact on C2 hydrocarbon production is attributed to the high surface coverage of O* from CO2 conversion, which occupies crucial active sites and impedes C-C couplings to C2 species over χ-Fe5C2(510). The coexistence of iron oxide and carbide phases was proposed and the interfacial sites created between the two phases impact CO2 surface chemistry. Adding potassium into the Fe5C2 catalyst accelerates O* removal from the carbide surface, enhances the stability of the iron carbide catalyst, thus, promotes C-C couplings to hydrocarbons.

The newly-assisted catalytic mechanism of surface hydroxyl species performed as the promoter in syngas-to-C2 species on the Cu-based bimetallic catalysts

In the conversion process of syngas-to-C2 species, the OH species are inevitably produced accompanying the production of key intermediates CHx (x = 1–3), traditionally, the function of surface OH species is generally accepted as the hydrogenating reactive species. This work for the first time proposed and confirmed the assisted catalytic mechanism of surface OH species that performed as the promoter for syngas-to-C2 species on Cu-based catalysts. DFT and microkinetic modeling results reveal that the produced OH species accompanying the intermediates CHx production on the MCu (M = Co, Fe, Rh) catalysts can stably exist to form OH/MCu catalysts, on which the presence of surface OH species as the promoter not only presented better activity and selectivity toward CHx (x = 1–3) compared to MCu catalysts, but also significantly suppressed CH3OH production, providing enough CHx sources to favor the production of C2 hydrocarbons and oxygenates. Correspondingly, the electronic properties analysis revealed the essential relationship between the electronic feature of OH/MCu catalysts and catalytic performance, attributing to the unique electronic micro−environment of the catalysts under the interaction of surface OH species. This new mechanism is called as OH-assisted catalytic mechanism, which may be applied in the reaction systems related to the generation of OH species.

Symmetry‐Broken Au–Cu Heterostructures and their Tandem Catalysis Process in Electrochemical CO2 Reduction

AbstractSymmetry‐breaking synthesis of colloidal nanocrystals with desired structures and properties has aroused widespread interest in various fields, but the lack of robust synthetic protocols and the complex growth kinetics limit their practical applications. Herein, a general strategy is developed to synthesize the Au–Cu Janus nanocrystals (JNCs) through the site‐selective growth of Cu nanodomains on Au nanocrystals, which is directed by the substantial lattice mismatch between them, with the assistance of judicious manipulation of the growth kinetics. This strategy can work on Au nanocrystals with different architectures for the achievement of diverse asymmetric Au–Cu hybrid nanostructures. Of particular note, the obtained Au nanobipyramids (Au NBPs)‐based JNCs facilitate the conversion of CO2 to C2 hydrocarbon production during electrocatalysis, with the Faradaic efficiency and maximum partial current density being 4.1‐fold and 6.4‐fold higher than those of their monometallic Cu counterparts, respectively. The excellent electrocatalytic performances benefit from the special design of the Au–Cu Janus architectures and their tandem catalysis mechanism as well as the high‐index facets on Au nanocrystals. This research provides a new approach to synthesize various hybrid Janus nanostructures, facilitating the study of structure‐function relationship in the catalytic process and the rational design of efficient heterogeneous electrocatalysts.

Direct conversion of methane to C2 hydrocarbons using W supported on sulfated zirconia solid acid catalyst

One of the most challenging aspects of modern day catalysis is the activation of methane. Conventionally, methane is activated with oxidizing agents to produce syngas, which then reacts to produce high value hydrocarbons. This process is energy inefficient. A more economic process is the direct one-step activation of methane to form value-added chemicals. This report focuses on direct conversion of methane to ethylene and ethane. Ethylene and ethane are the most important feedstocks in modern day chemical industries. Conventional process for ethylene production is via steam cracking of hydrocarbons, which is not an energy efficient approach. A direct conversion route from methane to C2 hydrocarbons would be a significant advance and has been widely studied. Mo supported on solid acids have been previously reported to be promising for direct conversion of methane to higher hydrocarbons. Here, a novel catalytic approach is introduced with W, a strong oxidizing agent, doped on sulfated zirconia solid acid and studied for the activation of methane at 650–750 °C. BET, DRIFTS, ammonia TPD, XPS, XRD and SEM–EDX were used to characterize the fresh catalyst. Reaction products are primarily ethylene and ethane, along with trace aromatics. Methane activation along with production of C2 hydrocarbons increased noticeably at higher temperature but deactivated due to carbon deposition as confirmed by TPO.

Plasma Oxidation of Cu for Electrochemical CO2 Reduction

Tuning the selectivity of copper-based catalysts towards the formation of C2 hydrocarbon products has become the main driving force in the development of CO2 reduction electrocatalysis. In particular, Oxide derived Cu (OD-Cu) has been proven to significantly increase the formation of C2 hydrocarbons, in which ethylene is produced at the expense of methane [1]. Further, the selectivity is tunable by controlling the oxide thickness and the ratio of Cu+ to Cu2+ [2]. Oxygen plasma have been especially successful in developing Cu-based catalysts since it gives a good control of the oxidation conditions. The large increase in surface roughness is also believed to stabilize Cu+ during the CO2 reduction reaction (CO2RR) [3]. The latter has shown to be a prerequisite for CO dimerization, due to the attractive forces resulting from the oppositely charged *CO on the Cu0 and Cu+ sites [4]. In this paper, we present a method for tuning the selectivity of Cu catalysts through a controlled oxidation process using oxygen plasma. The effect of plasma exposure time on the catalytic performance will be investigated.A plasma cleaner (Plasma Parylene Systems, Alpha Plasma AL18, Germany) was used to oxidize high purity copper foils (Jiarun Metal Material Corporation, China, 99.9999%) to prepare the catalysts. The plasma power was set to a constant 400 W in an O2 atmosphere at a pressure of 60 Pa, while varying the exposure time from 15 to 60 minutes. Prior to plasma oxidation, the Cu foils were cleaned in an ultrasonic bath of acetone for 25 minutes. Then, 10 minutes of Ar plasma (300 W at 38 Pa) were used prior to oxidation in order to remove any surface contaminants.Visually, the samples appear red, purple, and blue-grey for exposure times of 15, 30, and 60 minutes, respectively (figure 1). The sample exposed to oxygen plasma for 15 minutes has a granular morphology with clearly defined grains (~ 50 nm), which gradually grows together when doubling the exposure time to 30 minutes, and eventually leads to a continuous film when the exposure time reaches 60 minutes (figure 2). Electron Dispersion Spectroscopy (EDS) analysis shows a steady increase in oxygen concentration as a function of plasma time (figure 2). The visually observed color difference can be attributed to the difference in oxide concentration as well as the surface morphology of the samples, which can explain the untraditional colors of our copper oxides.The electrochemical measurements will be performed using an H-cell equipped with a Nafion 117 proton exchange membrane, where the cathodic and anodic compartments are each filled with 20 mL of 0.1M KHCO3, while CO2 is bubbled through the solution at a constant flow rate of 20 sccm. Catalytic performance is to be determined using an electrochemical workstation (CHI23213). Furthermore, quantification of the reaction products will be accomplished using a gas chromatograph (Shimadzu GC 2010 PLUS) equipped with a gas sampling valve (GSV) and a barrier discharge ionization (BID) detector. The experiments will be performed in an online configuration with a constant flow of CO2. In summary, this work will provide new insight into plasma-oxidized copper catalysts for electrochemical CO2 reduction.

Improving Artificial Photosynthesis over Carbon Nitride by Gas-Liquid-Solid Interface Management for Full Light-Induced CO2 Reduction to C1 and C2 Fuels and O2.

The activity and selectivity of simple photocatalysts for CO2 reduction remain limited by the insufficient photophysics of the catalysts, as well as the low solubility and slow mass transport of gas molecules in/through aqueous solution. In this study, these limitations are overcome by constructing a triphasic photocatalytic system, in which polymeric carbon nitride (CN) is immobilized onto a hydrophobic substrate, and the photocatalytic reduction reaction occurs at a gas–liquid–solid (CO2–water–catalyst) triple interface. CN anchored onto the surface of a hydrophobic substrate exhibits an approximately 7.2‐fold enhancement in total CO2 conversion, with a rate of 415.50 μmol m−2 h−1 under simulated solar light irradiation. This value corresponds to an overall photosynthetic efficiency for full water–CO2 conversion of 0.33 %, which is very close to biological systems. A remarkable enhancement of direct C2 hydrocarbon production and a high CO2 conversion selectivity of 97.7 % are observed. Going from water oxidation to phosphate oxidation, the quantum yield is increased to 1.28 %.

A Comparative Study on C2 Hydrocarbons and Methanol Synthesis from CO Hydrogenation Catalyzed by M1/W6S8 (M = Ir and Ca) Single-Atom Catalysts

Exploring highly selective catalysts for CO hydrogenation reactions remains a significant challenge as a critical stage in the conversion of CO resources into chemicals or fuels. Here, we provide guidelines on this issue, exploring the generation of major production in the CO hydrogenation process of M1/W6S8 (M = Ir and Ca) single-atom catalysts, and performing density functional calculations. Calculate the reaction energy and barrier for each basic step. Calculations represent that the Ca1/W6S8 catalyst is very advantageous for methanol synthesis (CO* + 4H* → CHO* + 3H* → CH2O* + 3H* → CH3O* + H* → CH3OH*). On the other hand, the Ir1/W6S8 catalyst strongly favors the production of C2 hydrocarbons. We use the harmonic transition state theory to calculate the rate constant of the subsequent step of converting CH3O* species on M1/W6S8 (M = Ir and Ca). The results of the rate constants are consistent with our kinetic results. These results add new insights into the basic understanding of complex CO hydrogenation reactions. A series of reactions starting from CO on the (a) Ir1/W6S8, (b) Ca1/W6S8. The activation barriers and reaction energies of the elementary steps are all shown in kcal/mol.

Insights into two-dimensional MoS2 sheets for enhanced CO2 photoreduction to C1 and C2 hydrocarbon products

Herein, hydrothermal synthesis of 2D structure of MoS2 sheets followed by a simple annealing step was reported. The XRD pattern revealed the co-existence of 2H and 3R MoS2 phases. FE-SEM clearly showed the observation of stacked layers of MoS2. Moreover, Raman analysis revealed that more than 10 layers stacking of MoS2 sheets was synthesized. Furthermore, XPS analysis confirmed the presence of Mo4+ species that belongs to MoS2. The CO2 photoreduction over MoS2 was operated under UV light and the results displayed a significant performance towards methanol and acetaldehyde production using different aqueous solutions. The maximum production yield of methanol was estimated to be 109.5 μmol/g in 0.5 M NaHCO3; however, acetaldehyde yield was 19.2 μmol/g in 0.5 M NaCl. The high-speed transition of excited electrons along MoS2 sheets would reflect a high separation between charge carriers, which addressed for the impressive photocatalytic performance of MoS2 to reduce CO2.

Valorization of chloromethanes by hydrodechlorination with metallic catalysts

The performance of Pd, Pt, Rh and Ru based catalysts in the hydrodechlorination of chloromethanes to obtain ethane and ethylene was evaluated by means of computational analysis and hydrodechlorination experiments. A computational analysis using density functional theory (DFT) was developed to obtain preliminary insight on the potential catalytic mechanisms for the reactions involved using palladium, platinum, rhodium and ruthenium metallic clusters. Stable catalytic intermediates were obtained by quantum-chemical calculations in the hydrodechlorination of dichloromethane on Pd6 and Rh6 clusters, presenting CH2 and CH3 radicals and C2H4, C2H6 and CH4 products. On the contrary, it was not possible to obtain all these stable intermediates using Pt6 and Ru6 clusters. Theoretical analysis revealed lower desorption energies for ethane and ethylene products in Pd6 than in Rh6 clusters, what indicates a favorable selectivity of Pd-based catalyst for desired C2 products. Then, carbon supported catalysts containing these four metals were prepared and experimentally evaluated in the hydrodechlorination of dichloromethane (DCM) and trichloromethane (TCM) at low H2 excess and a reaction temperature range of 150–400°C. In agreement with computational results, in experimental tests, the Pd based catalyst showed the best performance for the hydrodechlorination of chloromethanes to obtain C2 products, followed by Rh, Ru and Pt have a poor performance, in special Pt based catalyst, which shows almost no selectivity to C2 products. This computational and experimental study emphasizes, for the first time, the good performance (high activity and selectivity) of Pd carbon supported catalysts in the valorization of chloromethane compounds to obtain C2 hydrocarbon products.

(Invited) High-Temperature Electrosynthesis of Hydrogen and Chemicals

High-temperature electrochemical cells based on solid electrolytes have been considered for synthesis and production of hydrogen and a variety of other fuels and chemicals. Solid oxide electrolysis cells (SOECs) for example, are being developed for hydrogen production (from water), syngas production (from mixtures of water and carbon dioxide) and oxygen recovery (from water or carbon dioxide for space applications). The main attractive features of the SOEC are its simple chemistry, environmental compatibility and high electrical-to-hydrogen efficiency. Solid oxide fuel cell (SOFC type cells have been investigated for production of chemicals and cogeneration of electricity and chemicals (in this case, the cell is referred to as CSOFC); examples include production of C2 hydrocarbons and syngas from methane. The key features of the CSOFC include its high selectivity and the possibility to produce valuable chemicals such as hydrocarbons using methane-rich gases from non-fossil origins. Current state-of-the-art SOECs and CSOFCs, both fundamentally derived from the more advanced conventional SOFC technology are still in their feasibility/development stage. This paper discusses certain aspects in selected materials, performance and operation of the SOEC for hydrogen production from water and the CSOFC for production of C2 hydrocarbons from methane.

(Invited) High-Temperature Electrosynthesis of Hydrogen and Chemicals

High-temperature electrochemical cells based on solid electrolytes have been considered for synthesis and production of hydrogen and a variety of other fuels and chemicals. Solid oxide electrolysis cells (SOECs), for example, are being developed for hydrogen production (from water), syngas production (from mixtures of water and carbon dioxide) and oxygen recovery (from water or carbon dioxide for space applications). The main attractive features of the SOEC are its simple chemistry, environmental compatibility and high electrical-to-hydrogen efficiency. Solid oxide fuel cell (SOFC) type cells have been investigated for production of chemicals and cogeneration of electricity and chemicals (in this case, the cell is referred to as CSOFC); examples include production of C2 hydrocarbons and syngas from methane. The key features of the CSOFC include its high selectivity and the possibility to produce valuable chemicals such as hydrocarbons using methane-rich gases from non-fossil origins. Current state-of-the-art SOECs and CSOFCs, both fundamentally derived from the more advanced conventional SOFC technology, are still in their feasibility/development stage. This paper discusses certain aspects in selected materials, performance and operation of the SOEC for hydrogen production from water and the CSOFC for production of C2 hydrocarbons from methane.

Characterizing CO2 Reduction Mechanism Using Advanced Synchrotron-Based X-Ray Spectroscopy Techniques

Generation of solar fuels through photo-catalytic reduction of CO2 could simultaneously address both the need for sustainable and affordable energy sources and the necessity of reducing global CO2 footprint. Discovering and designing new catalysts that have both high activity and selectivity for CO2 reduction is the critical barrier to overcome in order for solar fuel generation processes to commercialize. So far, copper is the sole material known to efficiently catalyze conversion of CO2 to considerable amounts of C2 hydrocarbon products over time. However, CO2 reduction on Copper exhibits a high overpotential plus the added disadvantage of producing a mixture of several products including hydrogen.1,2 Thus, it is of vital importance to understand the so far ambiguous and poorly understood catalytic CO2 reduction mechanism on copper. In this work, a combination of various in-situ X-ray spectroscopy techniques are utilized to probe the electrode/electrolyte interface and provide insight into the reduction reaction.X-ray absorption spectroscopy (XAS) provides an element-specific probe of the conduction band via a core-level excitation into unoccupied electronic states and can reveal both oxidation state and details of the electronic structure. Operando Grazing incidence XAS at beamline 11-2 of SSRL is utilized to study the electrode surface at the metal K- and L-edges. A specially designed 3D printed flow cell maintainsa 300 micron liquid layer above the catalyst surface, enabling XAS characterization of the catalyst surface during electrochemistry in grazing incidence mode. The grazing incidence geometry provides a probe depth of about 5 nm into the catalyst, hence providing a highly surface sensitive spectroscopic tool. Preliminary measurements were conducted on the relatively inert surface of AuPd alloy catalyst. This is the first step in determining the feasibility of the study before examining the more complicated copper system. Distinct reversible shifts are observed in spectroscopic features with applied potential, which are believed to be due to H+ intercalation into Pd phase. (Figure 1) Further, operando soft X-ray spectroscopy measurements at C-edge are conducted at beamline 8.0.1 of ALS to detect intermediate carbon species. Electron yield soft XAS data are collected at a depth of 1 nm above the electrode surface in a specially designed in-situ electrochemical flow cell3. Strong 1s to π* transition in C edge spectra provides fingerprint for different products. First principles DFT calculations are conducted to characterize features obtained through these XAS measurements. (Figure 2) Combination of these spectroscopic techniques with electrochemical and theoretical calculations will paint a comprehensive picture of the exact CO2RR mechanism on Cu surface, which then can be used to design next generation photo-catalysts.

Oxidative Coupling of Methane over YSZ Support Catalysts for Application in C2 Hydrocarbon Production

This paper studies the development of Mn-Na2WO4 catalysts on YSZ support for oxidative coupling of methane reaction. It can be divided into two parts; (1) study in fixed bed reactor (FBR), and (2) study in solid oxide fuel cell reactor (SOFC). In part I, the experiments were performed using co-feeds of methane, oxygen and nitrogen inert gas at a ratio of 4:1:5 for different temperatures (973-1173 K). Mn-Na2WO4 catalyst on YSZ support was doped with sulfur, phosphorous, and cerium in order to improve its catalytic reactivity. The results indicated that sulfur and phosphorous showed the good improvement for Mn-Na2WO4 catalyst on YSZ support. At 1073 K, S-Mn-Na2WO4/YSZ provided C2 selectivity of 60.3% and methane conversion of 31.1%, while P-Mn- Na2WO4/YSZ offered C2 selectivity of 59.8% and methane conversion of 34.1%. P-Mn-Na2WO4/YSZ catalyst was selected as anode catalysts for further study in the SOFC reactor. The experiments were carried out using La0.8Sr0.2MnO3 (LSM) as the cathode catalyst, 8mol% yttria-stabilized zirconia (YSZ) as the electrolyte. P-Mn-Na2WO4/YSZ exhibited the best performance, providing C2H4 selectivity of 89.0%, methane conversion of 10.5% and maximum power density of 7.2 W/m2 at 1123 K. In addition, the stability of the P-Mn-Na2WO4/YSZ catalyst was tested at 1123 K. Good stability of the reaction system could be observed at least for 29 hours.

Light hydrocarbons production over bimetallic calcium–actinide oxide catalysts using N2O as oxidant

New bimetallic calcium–actinide (Th and U) oxides were synthesized and tested as catalysts for the oxidative coupling of methane (OCM) using nitrous oxide as oxidant. The reaction main products were primarily C2 hydrocarbons (C2H4 and C2H6), particularly over the bimetallic calcium–thorium oxide catalyst (CH4 conversion≈28%; C2 selectivity≈53%; C2 yield≈15% at 800°C). The selectivity to hydrocarbons is promoted when thorium replaces uranium on the bimetallic calcium–actinide oxides (at CH4 isoconversion=15±3%; C2 selectivity≈32% and 64% over the bimetallic Ca–U–O and Ca–Th–O catalysts at 750°C, respectively), which can be linked to the actinide oxide phase properties. The bimetallic calcium–actinide oxides catalytic performance correlates with their acid–base and conductivity properties (selectivity to hydrocarbons increases with the catalysts basicity and it is higher over p-type conductors, e.g. ThO2). The influence of the reaction temperature, gas phase CH4/N2O molar ratio and type of oxidant agent were also studied. In particular, the studies performed either under O2 or N2O confirm that the use of nitrous oxide improves the selectivity to hydrocarbons. To the best of our knowledge, this is the first time that an OCM study using N2O as oxidant agent is reported over bimetallic Ca–An (An=Th and U) oxides aiming the production of C2 hydrocarbons.

Oxidative coupling of methane over KCl–LnCl3 eutectic molten salt catalysts

Potassium-lanthanide chloride molten salts (KCl–LnCl3, Ln=La, Ce, Sm, Dy and Yb) were used as catalysts for the oxidation of methane with N2O. They proved to be active and selective for the production of C2 hydrocarbons (e.g. CH4 conversion≈15% and C2 selectivity>75% over the KCl–CeCl3 catalyst at 750°C) and remarkably stable for long periods of time on the gaseous stream (>48h). It was also found that their catalytic performance depends on the f block element (increases when La is replaced by Ce, Sm or Dy). The factors that seem to contribute to the variation of the activity and selectivity are the catalysts acid–base properties (higher acidity implies high activity, but lower selectivity to C2 hydrocarbons) and the oxidative character of the rare earth trivalent ions in the potassium chloride molten melt (high oxidation-reduction potentials implies lower activity and higher selectivity to hydrocarbons). The effect of the type of oxidant was also studied. The potassium-lanthanide chloride molten salts were more selective to hydrocarbons under N2O than under O2, e.g. ≈75 vs. ≈40% over KCl–CeCl3, respectively, which is clearly an advantage taking into account that nitrous oxide is a major greenhouse agent. To our knowledge, this is the first time that molten metal chloride catalysts were used as catalysts for the catalytic conversion of methane into hydrocarbons using N2O as oxidant.