Showing papers on "Partial oxidation published in 2019"
TL;DR: In this paper, copper was deposited on as well as encapsulated in a semiconductor-like MOF to fabricate the Cu/Cu@UiO-66 catalyst via an advanced double-solvent approach followed by one-step reduction.
Abstract: Metal-organic framework (MOF) is one of the most promising porous materials in photocatalysis. In this study, copper was deposited on as well as encapsulated in a semiconductor-like MOF (UiO-66) to fabricate the Cu/Cu@UiO-66 catalyst via an advanced double-solvent approach followed by one-step reduction. Even with ultralow amount of copper, Cu/Cu@UiO-66 shows significantly enhanced photocatalytic activity as well as stability for partial oxidation of aromatic alcohols under visible light irradiation. The result is attributed to the integration of plasmonic effect (Cu nanoparticles on UiO-66) and Schottky junction (Cu quantum dots encapsulated in UiO-66) which can be considered as a promising noble-metal-free way for the enhancement of visible-light-driven photocatalytic activity of MOFs.
159 citations
TL;DR: It is demonstrated that this reaction is catalyzed by a [Cu-O-Cu]2+ motif that forms via a hypothesized proton-aided diffusion of hydrated Cu ions within the cages of SSZ-13 zeolites, the primary active site for selective partial methane oxidation.
Abstract: Copper-exchanged zeolites can continuously and selectively catalyze the partial oxidation of methane to methanol using only oxygen and water at low temperatures, but the genesis and nature of the active sites are currently unknown. Herein, we demonstrate that this reaction is catalyzed by a [Cu-O-Cu]2+ motif that forms via a hypothesized proton-aided diffusion of hydrated Cu ions within the cages of SSZ-13 zeolites. While various Cu configurations may be present and active for methane oxidation, a dimeric Cu motif is the primary active site for selective partial methane oxidation. Mechanistically, CH4 activation proceeds via rate-determining C-H scission to form a surface-bound C1 intermediate that can either be desorbed as methanol in the presence of H2O/H+ or completely oxidized to CO2 by gas-phase O2. High partial oxidation selectivity can be obtained with (i) high methane and water partial pressures and (ii) maximizing Cu dimer formation by using zeolites with high Al content and low Cu loadings.
158 citations
TL;DR: The methodology is a unique alternative to tune the dehydration, oxidation, and properties of V2CTx, which allows for the expansion of applications of MXenes.
Abstract: We report on the thermal stability of multilayered V2CTx MXenes under different atmospheres by combining in situ Raman spectroscopy with ex situ X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) in order to elucidate and monitor the molecular, electronic, and structural changes of both the surface and bulk of the V2CTx MXene which has recently received much attention. The MXene samples were heated up to 600 °C in inert (N2), oxidative (CO2, air), and reductive (H2) environments under similar conditions. In situ Raman showed that the VO vibration for two-dimensional vanadia is preserved up to 600 °C under N2, while its intensity reduces under H2. When heated above 300 °C under either CO2 or air, V2CTx slightly oxidizes or transforms into V2O5, respectively. Furthermore, SEM revealed the presence of an accordion-like layered structure for the MXene under N2 and H2, while under CO2 and air the layered structure collapses and forms VO2 (V4+) and V2O5 (V5+) crystals, respectively. XPS reveals that, regardless of the gas, surface V species oxidize above 300 °C during the dehydration process. Finally, we demonstrated that the partial dehydration of V2CTx results in the partial oxidation of the material, and the total dehydration is achieved once 700 °C is reached. We believe that our methodology is a unique alternative to tune the dehydration, oxidation, and properties of V2CTx, which allows for the expansion of applications of MXenes.
104 citations
TL;DR: Wox/CeO2 catalysts prepared by wet impregnation with (NH4)6H2W12O40 and (COOH)2 aqueous solution were used in the catalytic combustion of chlorobenzene (CB) and 1, 2-dichloro- benzene (1,2-DCB) as mentioned in this paper.
Abstract: WOx/CeO2 catalysts prepared by wet impregnation with (NH4)6H2W12O40 and (COOH)2 aqueous solution were used in the catalytic combustion of chlorobenzene (CB) and 1,2-dichloro- benzene (1,2-DCB). Characterization by XRD, N2 isothermal adsorption and desorption, Raman, XPS, H2-TPR, O2-TPD and NH3-TPD shows that CeO2 exists as a form of face-centered cubic fluorite structure, while WOx is identified as the forms of monoxo and dioxo monotungstate, polytungstate and nano-particle, depending on W content. W-O-Ce is formed as a result of interaction between WOx and CeO2, which increases oxygen vacancy and promotes the reducibility and acidity of WOx/CeO2 catalysts. In CB or 1,2-DCB oxidation, WOx/CeO2 catalysts with monotungstate WOx present excellent stable activity with TOF at 250 °C based on W-O-Ce in a range of 4.7–7.2 × 10−4 s-1. 90% conversion is obtained below 350 °C, at which chlorination is almost completely inhibited. The activity in feed containing 5% H2O or 5% CO2 is depending on their effects on the availability of surface oxygen. In situ FT-IR shows that the adsorbed CB species can be oxidized by surface lattice oxygen into phenolate, carboxylates and carbonate, while the formation of acetaldehyde on Bronsted acid sites is promoted by gas oxygen. Partial oxidation products are oxidized to COx by surface oxygen.
94 citations
TL;DR: In this paper, Ni promoted ceria-titanium oxide (CeO2-TiO2) redox catalysts were developed for highly effective thermochemical CO2 and H2O splitting as well as partial oxidation of CH4 at 900 °C.
Abstract: Solar thermochemical approaches to CO2 and H2O splitting have emerged as an attractive pathway to solar fuel production. However, efficiently producing solar fuel with high redox kinetics and yields at lower temperature remains a major challenge. In this study, Ni promoted ceria–titanium oxide (CeO2–TiO2) redox catalysts were developed for highly effective thermochemical CO2 and H2O splitting as well as partial oxidation of CH4 at 900 °C. Unprecedented CO and H2 production rates and productivities of about 10–140 and 5–50 times higher than the current state-of-the-art solar thermochemical carbon dioxide splitting and water splitting processes were achieved with simultaneous close to complete CH4 conversions and high selectivities towards syngas. The underlying mechanism for the exceptional reaction performance was investigated by combined experimental characterization and density functional theory (DFT) calculations. It is revealed that the metallic Ni and the Ni/oxide interface manifest catalytic activity for both CH4 activation and CO2 or H2O dissociation, whereas CeO2–TiO2 enhances the lattice oxygen transport via the CeO2–TiO2/Ce2Ti2O7 stoichiometric redox cycle for CH4 partial oxidation and the subsequent CO2 or H2O splitting promoted by catalytically active Ni. Such findings substantiate the significance of the synergy between the reactant activation by catalytic sites and the stoichiometric redox chemistry governing oxygen ion transport, paving the way for designing prospective materials for sustainable solar fuel production.
78 citations
TL;DR: The metal-oxo moieties are important catalytic intermediates in the selective partial oxidation of hydrocarbons and in water splitting, and they have reactive properties that vary depen...
Abstract: Metal–oxo moieties are important catalytic intermediates in the selective partial oxidation of hydrocarbons and in water splitting. Stable metal–oxo species have reactive properties that vary depen...
72 citations
TL;DR: In this article, the solar-driven chemical looping methane reforming using the non-stoichiometric ceria redox cycle was experimentally investigated for both syngas production and isothermal H2O/CO2 splitting using a directly irradiated volumetric solar reactor in the temperature range of 950-1050°C.
71 citations
TL;DR: In this paper, a mesoporous silica supported nanoparticle-oxygen carrier was proposed to suppress the co-production of CO2 in methane partial oxidation reactions using iron oxide nanoparticles embedded in mesopore silica matrix.
Abstract: Chemical looping methane partial oxidation provides an energy and cost effective route for methane utilization. However, there is considerable CO2 co-production in current chemical looping systems, rendering a decreased productivity in value-added fuels or chemicals. In this work, we demonstrate that the co-production of CO2 can be dramatically suppressed in methane partial oxidation reactions using iron oxide nanoparticles embedded in mesoporous silica matrix. We experimentally obtain near 100% CO selectivity in a cyclic redox system at 750–935 °C, which is a significantly lower temperature range than in conventional oxygen carrier systems. Density functional theory calculations elucidate the origins for such selectivity and show that low-coordinated lattice oxygen atoms on the surface of nanoparticles significantly promote Fe–O bond cleavage and CO formation. We envision that embedded nanostructured oxygen carriers have the potential to serve as a general materials platform for redox reactions with nanomaterials at high temperatures. Chemical looping methane partial oxidation is an effective technology to produce syngas with a minimal energy penalty. Here, the authors design and develop a mesoporous silica supported nanoparticle oxygen carrier that enables a near 100% CO generation with high recyclability and substantially lower operating temperature.
68 citations
TL;DR: In this article, the authors present the synthesis and characterization of novel manganese (IV) oxide nanorods as a catalyst for the 5-hydroxymethylfurfural (HMF) to DFF partial oxidation at ambient conditions.
Abstract: The valorization of natural and renewable resources, like lignocellulosic biomass, towards value-added chemicals by low energy and economically viable processes still remains a global research and technological challenge. 5-hydroxymethylfurfural (HMF) is an important platform chemical that can be easily derived from biomass, and it can be further used as a feedstock for the production of building blocks for polymers or fuels. In this context, the partial oxidation of the hydroxyl group on the HMF molecule leads to the formation of the corresponding aldehyde, 2,5-diformylfuran (DFF), which may find multiple applications in bio-chemical industries. Herein, we present the synthesis and characterization of novel manganese (IV) oxide nanorods as catalyst for the HMF to DFF partial oxidation at ambient conditions. This 1D nanocatalyst operates at low energy light irradiation and without the addition of chemicals (bases or oxidants) as a highly selective photo-assisted catalyst. Under optimized experimental conditions, the HMF conversion was found to be above 99%, while the DFF selectivity was almost 100%. The presence of molecular O2 played a key role in triggering the selective oxidation, while the use of an aprotic and less polar organic solvent, such as acetonitrile, compared to water, further enhanced the reactivity of the catalyst.
67 citations
TL;DR: This mini-review focused on the direct methane oxidation to methanol over copper-loaded zeolite systems, which mimics facile enzymatic chemistry of methane oxidation and the consensus among the researchers to achieve the target of high meethanol yield is discussed.
Abstract: The conversion of methane into an easily transportable liquid fuel or chemicals has become a highly sought-after goal spurred by the increasing availability of cheap and abundant natural gas. While utilization of methane for the production of syngas and its subsequent conversion via an indirect route is typical, it is cost-intensive, and alternative direct conversion routes have been investigated actively. One of the most promising directions among these is the low-temperature partial oxidation of methane to methanol over a metal-loaded zeolite, which mimics facile enzymatic chemistry of methane oxidation. Thus mono-, bi-, and trinuclear oxide compounds of iron and copper stabilized on ZSM-5 or mordenite, which are structurally analogous to those found in methane monooxygenases, have demonstrated promising catalytic performances. The two major problems of theses metal-loaded zeolites are low yield to methanol and batch-like non-catalytic reaction systems challenging to extend to an industrial scale. In this mini-review, attention was given to the direct methane oxidation to methanol over copper-loaded zeolite systems. A brief introduction on the catalytic methane direct oxidation routes and current status of the applied metal-containing zeolites including the ones with copper ions are given. Next, by analyzing the extensive experimental and theoretical data available, the consensus among the researchers to achieve the target of high methanol yield is discussed in terms of zeolite topology, active species, and reaction parameters. Finally, the recent efforts on continuous methanol production from the direct methane oxidation aiming for an industrial process are summarized.
67 citations
TL;DR: The 5Mo/H-ZSM-5 catalysts exhibited the best catalytic performance for methane conversion and benzene yield for methane dehydroaromatization at 700°C as discussed by the authors.
Abstract: Of several Mo/H-ZSM-5 catalysts (Mo loading = 1, 3, 5, 7 wt%), 5Mo/H-ZSM-5 (5 wt%) exhibited the best catalytic performance for methane conversion and benzene yield for methane dehydroaromatization at 700 °C It was observed that deactivation of zeolite acid sites precedes deactivation of the Mo2C sites Increasing the number of accessible Mo carbide sites with minimizing isolated surface acid sites is required for high benzene selectivity and stability Under oxidative conditions, bifunctional metal-acid sites were reversibly regenerated at 450 °C; at higher temperatures of 550–850 °C, irreversible deactivation was observed The selective recovery of Bronsted acid sites near Mo sites other than isolated acid sites is sufficient to restore the catalytic activity in terms of benzene formation Spectroscopic studies revealed that high-temperature oxidative regeneration induced (MoO42−)n oligomerization and subsequent carburization of bulk Mo carbide cluster The 5Mo/H-ZSM-5 underwent MoO3 sublimation and loss of Bronsted acidity during oxidative regeneration at 850 °C Reductive regeneration required a temperature higher than 700 °C for coke removal, but resulted in thermal degradation of the catalyst Theoretical calculations indicated that partial oxidation of coke precursor (ie naphthalene) at 450 °C was more favorable than its partial hydrogenation at 850 °C on the Mo clusters in ZSM-5 channel Overall, oxidative regeneration at 450 °C can maintain high Mo2C dispersion and efficient coke removal during 60 h of methane reaction
TL;DR: In this article, the bimetallic CaO/Fe2O3 oxygen carriers (OCs) were tested in a batch fluidized bed reactor using coal (char) as the fuel, and it was found that the char gasification rate is closely dependent on both lattice oxygen donation ability and catalytic activity of OCs.
TL;DR: In this article, single-atom alloys that possess unique dehydrogenation selectivity towards ethanol (EtOH) partial oxidation were designed using knowledge of the alloying effects from density functional theory calculations.
Abstract: Recently, we found that the atomic ensemble effect is the dominant effect influencing catalysis on surfaces alloyed with strong- and weak-binding elements, determining the activity and selectivity of many reactions on the alloy surface. In this study we design single-atom alloys that possess unique dehydrogenation selectivity towards ethanol (EtOH) partial oxidation, using knowledge of the alloying effects from density functional theory calculations. We found that doping of a strong-binding single-atom element (e.g., Ir, Pd, Pt, and Rh) into weak-binding inert close-packed substrates (e.g., Au, Ag, and Cu) leads to a highly active and selective initial dehydrogenation at the α-C–H site of adsorbed EtOH. We show that many of these stable single-atom alloy surfaces not only have tunable hydrogen binding, which allows for facile hydrogen desorption, but are also resistant to carbon coking. More importantly, we show that a rational design of the ensemble geometry can tune the selectivity of a catalytic reaction.
TL;DR: In this article, photo-assisted microbial fuel cells (MFCs) operated sequentially under anaerobic - aerobic processes, in the presence of Fe(III) and W and Mo oxides catalytic species.
Abstract: The intensification of the degradation and mineralization of the azo dye methyl orange (MO) in contaminated water with simultaneous production of renewable electrical energy was achieved in photo-assisted microbial fuel cells (MFCs) operated sequentially under anaerobic - aerobic processes, in the presence of Fe(III) and W and Mo oxides catalytic species. In this novel process, the W and Mo oxides deposited on the graphite felt cathodes accelerated electron transfer and the reductive decolorization of MO. Simultaneously, the mineralization of MO and intermediate products was intensified by the production of hydroxyl radicals (HO ) produced by (i) the photoreduction of Fe(III) to Fe(II), and by (ii) the reaction of the photochemically and electrochemically produced Fe(II) with hydrogen peroxide, which was produced in-situ during the aerobic stage. Under anaerobic conditions, the reductive decolorization of MO was driven by cathodic electrons, while the partial oxidation of the intermediates proceeded through holes oxidation, producing N,N-dimethyl-p-phenylenediamine. In contrast, under aerobic conditions superoxide radicals (O2 −) were predominant to HO , forming 4-hydroxy-N,N-dimethylaniline. In the presence of Fe(III) and under aerobic conditions, the oxidation of the intermediate products driven by HO superseded that of O2 −, yielding phenol and amines, via the oxidation of 4-hydroxy-N,N-dimethylaniline and N,N-dimethyl-p-phenylenediamine. These sequential anaerobic and electro-Fenton processes led to the production of benzene and significantly faster oxidation reactions, compared to either the anaerobic or the aerobic operation in the presence of Fe(III). Complete degradation and mineralization (96.8 ± 3.5%) of MO (20 mg/L) with simultaneous electricity production (0.0002 kW h/kg MO) was therefore achieved with sequential anaerobic (20 min) - aerobic (100 min) operation in the presence of Fe(III) (10 mg/L). This study demonstrates an alternative and environmentally benign approach for efficient remediation of azo dye contaminated water with simultaneous production of renewable energy.
TL;DR: Pt-xW/CeO2 catalysts, prepared by co-impregnation with aqueous solutions of (NH4)6-H2W12O40 and H2PtCI6, were applied in the catalytic oxidation of benzene (B), chlorobenzene (CB), and 1,2-dichlorobensene (1,2)-DCB, and characterisation by various methods identified CeO2 as cubic fluorite, and WOx in the form of monoxo monotungstate as discussed by the authors.
TL;DR: The catalytic behavior of nickel-based catalysts supported on different oxide substrates synthesized via wet impregnation and solid-state reaction, and the impact of Rh doping was investigated, found that the presence of Rh favors nickel reduction, which leads to an increase in the methane conversion and yield.
Abstract: There is great economic incentive in developing efficient catalysts to produce hydrogen or syngas by catalytic partial oxidation of methane (CPOM) since this is a much less energy-intensive reaction than the highly endothermic methane steam reforming reaction, which is the prominent reaction in industry. Herein, we report the catalytic behavior of nickel-based catalysts supported on different oxide substrates (Al2O3, CeO2, La2O3, MgO, and ZrO2) synthesized via wet impregnation and solid-state reaction. Furthermore, the impact of Rh doping was investigated. The catalysts have been characterized by X-ray diffraction, N2 adsorptiondesorption at -196°C, temperature-programmed reduction, X-ray photoelectron spectroscopy, O2-pulse chemisorption, transmission electron microscopy, and Raman spectroscopy. Supported Ni catalysts were found to be active for CPOM but can suffer from fast deactivation caused by the formation of carbon deposits as well as via the sintering of Ni nanoparticles (NPs). It has been found that the presence of Rh favors nickel reduction, which leads to an increase in the methane conversion and yield. For both synthesis methods, the catalysts supported on alumina and ceria show the best performance. This could be explained by the higher surface area of the Ni NPs on the alumina surface and presence of oxygen vacancies in the CeO2 lattice, which favor the proportion of oxygen adsorbed on defect sites. The catalysts supported on MgO suffer quick deactivation due to formation of a NiO/MgO solid solution, which is not reducible under the reaction conditions. The low level of carbon formation over the catalysts supported on La2O3 is ascribed to the very high dispersion of the nickel NPs and to the formation of lanthanum oxycarbonate, through which carbon deposits are gasified. The catalytic behavior for catalysts with ZrO2 as support depends on the synthesis method; however, in both cases, the catalysts undergo deactivation by carbon deposits.
TL;DR: In this article, a chemical looping dry reforming process for co-production of hydrogen and syngas was proposed, which consists of four different stages, i.e. reduction, dry reforming, steam oxidation and air oxidation.
TL;DR: In this article, a family of perovskite-type oxides La1-xSrxFeO3 (x ǫ = 0.1, 0.3, 0, 5, 0., 0.7, 1.0) were reported as effective redox catalysts for methane partial oxidation and thermochemical water splitting in a cyclic redox scheme.
TL;DR: In this article, a series of nonnoble-metal co-catalysts based on Co, Mn, Ni and Fe oxides were prepared by wet impregnation of the corresponding acetylacetonate precursors onto a model TiO2 substrate, followed by their oxidative decomposition.
Abstract: Here we report a systematic study of a series of non-noble-metal co-catalysts based on Co, Mn, Ni and Fe oxides that were prepared by wet impregnation of the corresponding acetylacetonate precursors onto a model TiO2 substrate, followed by their oxidative decomposition. We analyze thermal evolution of the impregnated M(acac)x–TiO2 composites with a combination of analytical methods and reveal strong differences in the precursor decomposition onsets and the resulting product composition, compared to the case of pure M(acac)x precursors. Consequent electron microscopy analyses of the resulting MOx–TiO2 composites indicate the presence of small (1–5 nm) amorphous MOx nanoparticles that are homogeneously distributed on the surface of the substrate TiO2. Complementing Raman and photoluminescence (PL) spectra confirm pronounced effects of MOx deposition on the state of TiO2 substrate and suggest strong electronic communication between the components. The composites obtained at 350 °C were further tested towards sacrificial hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) demonstrating the dynamic nature of the NiOx–TiO2 photocatalyst whose Ni0 active HER sites were generated in situ upon light exposure. In contrast, FeOx–TiO2, CoOx–TiO2, and NiOx–TiO2 were all active towards OER, featuring water oxidation ability in descending order, while XPS data of the samples after reaction indicate that partial oxidation of M species takes place during the course of the photocatalytic experiment. This work provides detailed insights on the wet chemistry-based preparation of MOx co-catalysts decorating oxide nanopowders including optimization of the thermal treatment, potential substrate effects and synergy as well as further prospects in photocatalysis.
TL;DR: In this paper, a robust solid oxide electrolysis cell with Sr2Fe1.5Mo0.6−δ−Ce0.8Sm0.2O1.9 (SFM-SDC) based electrodes has been utilized to verify the conceptual process of partial oxidation of methane (POM) assisted steam electrolysis, which can produce syngas and hydrogen simultaneously.
Abstract: In this work, a robust solid oxide electrolysis cell with Sr2Fe1.5Mo0.5O6−δ–Ce0.8Sm0.2O1.9 (SFM–SDC) based electrodes has been utilized to verify the conceptual process of partial oxidation of methane (POM) assisted steam electrolysis, which can produce syngas and hydrogen simultaneously. When the cathode is fed with 74%H2–26%H2O and operated at 850 °C, the open circuit voltage (OCV), the minimum energy barrier required to overcome the oxygen partial gradient, is remarkably reduced from 0.940 to −0.012 V after changing the feed gas in the anode chamber from air to methane, indicating that the electricity consumption of the steam electrolysis process could be significantly reduced and compensated by the use of low grade thermal energy from external heat sources. It is found that after ruthenium (Ru) impregnation, the electrolysis current density of the electrolyzer is effectively enhanced from −0.54 to −1.06 A cm−2 at 0.6 V and 850 °C, while the electrode polarization resistance under OCV conditions and 850 °C is significantly decreased from 0.516 to 0.367 Ω cm2. Long-term durability testing demonstrates that no obvious degradation but a slight improvement is observed for the electrolyzer, which is possibly due to the activation of the SFM–SDC electrode during operation. These results indicate that the robust Ru infiltrated solid oxide electrolyzer is a very promising candidate for POM assisted steam electrolysis applications. Our result will provide insight to improve the electrode catalysts used in POM assisted steam electrolysis.
TL;DR: In this article, a single-cylinder engine operated in homogeneous charge compression-ignition (HCCI) mode on a mixture of methane and air with dimethyl ether (DME) as a reactivityenhancing additive was used to generate synthesis gas.
TL;DR: In this article, single-atom catalysis has been a topic of increasing interest due to the potential for improved selectivity, reactivity, and catalyst cost, however, single atom catalysts are still difficult to construct.
Abstract: Single-atom catalysis has been a topic of increasing interest due to the potential for improved selectivity, reactivity, and catalyst cost. However, single-atom catalysts are still difficult to cha...
TL;DR: In this paper, Pd-Ru and Pt-Ru bimetallic catalysts with low metal content (0.5%) supported on commercial γ-Al2O3 and FAU zeolite prepared by hydrothermal method were synthesized and characterized to transform 5-hydroxymethylfurfural (HMF) into valuable chemicals under mild reaction conditions.
TL;DR: In this article, a chemical looping partial oxidation of CH4 is proposed for producing syngas with a suitable H2/CO ratio and avoiding the risk of explosion and use of an expensive air separation plant.
Abstract: Chemical looping partial oxidation of CH4 is a promising method for producing syngas with a suitable H2/CO ratio and avoiding the risk of explosion and use of an expensive air separation plant. How...
TL;DR: In this article, the authors investigated the performance of C3N4-TiO2 photo-catalyst embedded in a dense Nafion matrix in terms of productivity, selectivity and converted carbon.
Abstract: We investigated CO2 photocatalytic reduction coupling, for the first time in literature, the assets offered by the continuous operating mode using C3N4-TiO2 photo-catalyst embedded in a dense Nafion matrix. The reactor performance was analyzed under UV–vis light in terms of productivity, selectivity and converted carbon. Reaction pressure was specifically investigated for its effect as a “driver” in determining reactor performance, modulating products removal from the reaction volume. In addition, the membrane reactor performance was explored as a function of H2O/CO2 feed molar ratio and contact time. The higher feed pressure (5 bar) led to a lesser MeOH production and a greater amount of HCHO, owing to a hindered desorption, which promoted partial oxidation reactions. Total converted carbon instead did not vary significantly with reaction pressure. Membrane reactor with C3N4-TiO2 photocatalyst resulted more performant than other photocatalytic membrane reactors in terms of carbon converted (61 μmol gcatalyst−1 h−1).
TL;DR: Both pristine and iodine-doped NiTAA-MOF synthesized in this work could find potential applications in areas such as catalase mimics, catalysis, energy storage, and dynamic nuclear polarization-nuclear magnetic resonance (DNP-NMR).
Abstract: We report the synthesis and characterization of a two-dimensional (2D) conjugated Ni(II) tetraaza[14]annulene-linked metal organic framework (NiTAA-MOF) where NiTAA is a macrocyclic MN4 (M = metal,...
TL;DR: A mesoporous silica supported nanoparticle oxygen carrier that enables a near 100% CO generation with high recyclability and substantially lower operating temperature and envision that embedded nanostructured oxygen carriers have the potential to serve as a general materials platform for redox reactions with nanomaterials at high temperatures.
Abstract: Chemical looping methane partial oxidation provides an energy and cost effective route for methane utilization. However, there is considerable CO2 co-production in state-of-the-art chemical looping systems, rendering a decreased productivity in value-added fuels or chemicals. In this work, we show that the co-production of CO2 can be dramatically suppressed in methane partial oxidation reactions using iron oxide nanoparticles, with a size of 2~8 nm, as the oxygen carrier. To stabilize these nanoparticles at high temperatures, they are embedded in an ordered, gas-permeable mesoporous silica matrix. We experimentally obtained near 100% CO selectivity in a cyclic redox system at 750°C to 935°C, which is a significantly lower temperature range than in conventional oxygen carrier systems. Density functional theory calculations elucidate the origins for such selectivity and reveal that CH4 adsorption energies decrease with increasing nanoparticle size. These calculations also show that low-coordinated lattice oxygen atoms on the surface of nanoparticles significantly promote Fe-O bond cleavage and CO formation. We envision that embedded nanostructured oxygen carriers have the potential to serve as a general materials platform for achieving 100% selectivity in redox reactions at high temperatures.
TL;DR: In this paper, four different C3N4 specimens have been prepared, a bulk one (MCN), a thermally etched (TE), a solid prepared by hydrothermally treating MCN with H2O2, and a polymeric carbon nitride-hydrogen peroxide adduct, and the principal aim of this work was to correlate the capability of the prepared material to generate reactive oxygen species (ROS), under irradiation, with their photocatalytic activities in terms of conversion and selectivity for partial oxidation reactions.
TL;DR: In this article, in situ Fourier transform infrared (FTIR) and X-ray absorption spectroscopy (XAS) techniques highlighted the effect of Rh in facilitating C-C bond splitting in the ternary PtRh/SnO2 catalyst.
Abstract: Despite its attractive features as a power source for direct alcohol fuel cells, utilization of ethanol is still hampered by both fundamental and technical challenges. The rationale behind the slow and incomplete ethanol oxidation reaction (EOR) with low selectivity towards CO2 on most Pt-based catalysts is still far from being understood, and a number of practical problems need to be addressed before an efficient and low-cost catalyst is designed. Some recent achievements towards solving these problems are presented. Pt film electrodes and Pt monolayer (PtML) electrodes on various single crystal substrates showed that EOR follows the partial oxidation pathway without C-C bond cleavage, with acetic acid and acetaldehyde as the final products. The role of the substrate lattice on the catalytic properties of PtML was proven by the choice of appropriate M(111) structure (M = Pd, Ir, Rh, Ru and Au) showing enhanced kinetics when PtML is under tensile strain on Au(111) electrode. Nanostructured electrocatalysts containing Pt-Rh solid solution on SnO2 and Pt monolayer on non-noble metals are shown, optimized, and characterized by in situ methods. Electrochemical, in situ Fourier transform infrared (FTIR) and X-ray absorption spectroscopy (XAS) techniques highlighted the effect of Rh in facilitating C-C bond splitting in the ternary PtRh/SnO2 catalyst. In situ FTIR proved quantitatively the enhancement in the total oxidation pathway to CO2, and in situ XAS confirmed that Pt and Rh form a solid solution that remains in metallic form through a wide range of potentials due to the presence of SnO2. Combination of these findings with density functional theory calculations revealed the EOR reaction pathway and the role of each constituent of the ternary PtRh/SnO2 catalyst. The optimal Pt:Rh:Sn atomic ratio was found by the two in situ techniques. Attempts to replace Rh with cost-effective alternatives for commercially viable catalysts has shown that Ir can also split the C-C bond in ethanol, but the performance of optimized Pt-Rh-SnO2 is still higher than that of the Pt-Ir-SnO2 catalyst.
TL;DR: In this article, the authors present recent advances of CPOX techniques from bench to pilot scale and a comparison of its energy efficiency, carbon conversion efficiency, and operating costs with parallel technologies including steam reforming (SMR), autothermal reforming (ATR), and partial oxidation (POX).