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•Mo2C-supported catalysts exhibit activity for CO2 hydrogenation in liquid solvents.•Catalytic performance is significantly influenced by the type of metal deposition.•Hydrocarbons ...and methanol are produced via different intermediates/sites.•Metal/Mo2C catalysts display excellent bulk, surface, and catalytic stabilities.
A series of M/Mo2C (M=Cu, Pd, Co and Fe) were synthesized and evaluated for CO2 hydrogenation at 135–200°C in liquid 1,4-dioxane solvent. The Mo2C served as both a support and a co-catalyst for CO2 hydrogenation, exhibiting turnover frequencies of 0.6×10−4 and 20×10−4s−1 at 135 and 200°C, respectively. Methanol was the major product at 135°C, while CH3OH, C2H5OH, and C2+ hydrocarbons were produced at 200°C. The addition of Cu and Pd onto the high surface area Mo2C enhanced the production of CH3OH, while Co and Fe enhanced the production of C2+ hydrocarbons. Results for CO2, CO, and CH3OH hydrogenation experiments suggested that CO2 was the primary source for CH3OH while CO was the intermediate to hydrocarbons during CO2 hydrogenation. Characterization of the spent M/Mo2C catalysts revealed very little change in the surface and bulk chemistries and structures, indicating their stability in the liquid environment.
Redox flow batteries are attractive for large-scale energy storage due to a combination of high theoretical efficiencies and decoupled power and energy storage capacities. Efforts to significantly ...increase energy densities by using nonaqueous electrolytes have been impeded by separators with low selectivities. Here, we report nanoporous separators based on aramid nanofibres, which are assembled using a scalable, low cost, spin-assisted layer-by-layer technique. The multilayer structure yields 5 ± 0.5 nm pores, enabling nanofiltration with high selectivity. Further, surface modifications using polyelectrolytes result in enhanced performance. In vanadium acetylacetonate/acetonitrile-based electrolytes, the coated separator exhibits permeabilities an order of magnitude lower and ionic conductivities five times higher than those of a commercial separator. In addition, the coated separators exhibit exceptional stability, showing minimal degradation after more than 100 h of cycling. The low permeability translates into high coulombic efficiency in flow cell charge/discharge experiments performed at cycle times relevant for large-scale applications (5 h).
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•MgO, CaO, SiO2, and Al2O3 nanoparticles were prepared by Pechini-type Sol − Gel method.•Adsorption of two types of asphaltenes extracted from Iranian crude oils was studied.•Types of ...nanoparticles and asphaltenes significantly affect the adsorption process.•Adsorption capacities of the materials decreased in the order of SiO2 > MgO > Al2O3 > CaO.•Basic sites and textural properties significantly affect the adsorbent performance.
Basic, amphoteric, and acidic metal oxide nanoparticles including MgO, CaO, SiO2 and Al2O3 were synthesized via the Pechini-type sol–gel process and evaluated for adsorption of two types of asphaltenes (Ap1, Ap2) extracted from two different Iranian crude oils. The adsorbents were characterized by the N2 adsorption–desorption, XRD, FE-SEM, TEM, and EDS and the asphaltene samples were examined using FTIR analysis. The effects of citric acid to metal precursor molar ratio (M), calcination temperature, type of adsorbent, textural properties, adsorption temperature, and regeneration on the adsorbent performance were investigated. The SiO2 nanoparticle with the highest specific surface area and an amphoteric character was an excellent adsorbent capable of removing more than 70% of asphaltene from a model oil with initial asphaltene concentration of 3000 ppm. However, CaO exhibited the highest specific adsorption capacity, indicating that basic sites were active centers for asphaltene adsorption. It was demonstrated that with increasing the calcination temperature, the crystallite sizes of MgO and SiO2 increased and their BET surface areas decreased. The maximum asphaltene adsorption capacities of MgO and SiO2 nanoparticles were obtained at optimal calcination temperatures of 600 °C and 500 °C, respectively. Moreover, the optimum M value for the synthesis of MgO nanoparticle, in terms of asphaltene adsorption capacity, was M = 1, while it was M = 2 (for Ap1) and M = 1 (for Ap2) for SiO2. The adsorption isotherms were best fitted by the Jovanovic model. Moreover, kinetic data for the best adsorbents (MgO and SiO2) were in maximum agreement with the Elovich model. The adsorbents could be easily regenerated by calcination at 600 °C.
Research described in this paper targeted a cascade system for the hydrogenation of CO2 to methanol via formic acid and/or formate intermediates, a reaction sequence that has been accomplished ...previously using homogeneous catalysts. On the basis of results for the hydrogenation of CO2, formic acid, and ethyl formate over a series of Cu- and Mo2C-based catalysts, we selected a Cu chromite catalyst for CO2 hydrogenation to the formate and a Cu/Mo2C catalyst to convert the formate to methanol. These catalysts worked cooperatively in the presence of ethanol, yielding a methanol turnover frequency of 4.7 × 10–4 s–1 at 135 °C, 10 bar of CO2, and 30 bar of H2 in 1,4-dioxane. The performance for this Cu chromite:Cu/Mo2C cascade system surpassed the additive production of the individual catalysts by ∼60%. The results also allowed an investigation of the reaction pathways. The hydrogenation of CO2 to formic acid appeared to be the rate-limiting step for most of the catalysts. This is not surprising given the thermodynamics for this reaction. Finally, the hydrogenation of CO2 to dimethyl ether was also demonstrated using a system consisting of the Cu/Mo2C catalyst to produce methanol from CO2 and HZSM-5 to produce dimethyl ether from methanol. The systems described in this paper are, to our knowledge, the first demonstrating cascade CO2 hydrogenation via heterogeneous catalysts.
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•Fischer–Tropsch synthesis over Mo, W, V, and Nb carbides and nitrides is performed.•Rates decrease as follows: Mo2C∼W2C∼VN∼NbN>Mo2N∼W2N≫VC∼NbC.•Carbides and nitrides of the same ...parent metal exhibit very different TOFs for FTS.•Mo2N exhibits a larger activation barrier for CO dissociation than Mo2C.•Molecular COads facilitated coupling over Mo2C, supporting the oxygenate mechanism.
A series of transition metal carbide and nitride catalysts (Mo2C, Mo2N, W2C, W2N, VC, VN, NbC, and NbN) were prepared and evaluated for Fischer–Tropsch synthesis. The activity trend was Mo2C∼W2C∼VN∼NbN>Mo2N∼W2N≫VC∼NbC, with carbides and nitrides of the same parent metal exhibiting significantly different turnover frequencies (TOF). For example, the Mo2C catalyst exhibited a TOF of 0.36s−1 at 300°C whereas the TOF for the Mo2N catalyst was 0.04s−1. The carbides and nitrides favored light hydrocarbons (C1–C4) exhibiting α values between 0.31 and 0.43 at 290°C, and were active for the water–gas shift reaction. Results from temperature programmed desorption and reaction indicated that both the Mo2N and Mo2C catalysts are capable of direct (without H2 assistance) CO dissociation; however, the activation barrier is much higher over Mo2N than Mo2C. The results also indicate that C–C coupling over the Mo2C surface was facilitated by molecularly adsorbed CO (without H2 pre-adsorption), suggesting the primary pathway to C2+ hydrocarbons was through the oxygenate mechanism.
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•Hydrophobic fluorinated TiO2−WO3−Bi2O3/SiO2 nanocomposite was successfully prepared.•Fluorinated TiO2−WO3−Bi2O3/SiO2 material acts as both a photocatalyst and adsorbent.•Fluorinated ...nanocomposite indicated changes in PZC toward low pH.•Fluorinated sample showed efficient activity for degradation of RhB under visible light.•Enhanced adsorption capacity was observed as consequence of fluorination process.
Mesoporous silica-supported TiO2−WO3−Bi2O3 nanocomposites were prepared using wet impregnation and hydrophobically modified via a simple fluorination process using ammonium fluoride (NH4F) as the fluorination agent. The photocatalytic performance of the materials was evaluated in a triple-walled immersion well reactor for removal of Rhodamine B (RhB) dye using visible light. The bulk structures and surface properties of the materials were characterized by XRD, FE-SEM, HR-TEM, SAED pattern, EDS, N2 adsorption-desorption, FTIR, Zeta potential, DRS, PL, and water contact angle measurements. The FTIR spectra exhibited the incorporation of TiO2 nanoparticles and the fluoride ion into the fluorinated nanocomposites. Water contact angle and Zeta potential measurements of fluorinated samples indicated the enhanced surface hydrophobicity, the changes in point of zero charge (PZC) toward lower pH, and the increased negative surface charge. The performance of the TSWBi nanocomposites varied appreciably upon surface fluorination (TSWBi-F1) and displayed 93% RhB removal after only 30 min of visible light irradiation. RhB was adsorbed on the TSWBi-F1 and therefore, the material acts as both an adsorbent and photocatalyst simultaneously. Fluorinated SiO2 support was an excellent adsorbent, providing better sites for surface enrichment and adsorption of RhB molecules, while TiO2 nanoparticles promoted by WO3 and Bi2O3 behaved as visible light-active photocatalytic sites that could successfully degrade the RhB molecules adsorbed by the adjacent fluorinated SiO2 nanoparticles. Furthermore, the highly accessible surface area and mesoporous texture of the TSWBi-F1 could render more adsorptive and photocatalytic active centers and efficient mass transport of reacting molecules, respectively.
The development of nonaqueous redox flow batteries (NRFBs) has been impeded by a lack of electroactive compounds (anolytes and catholytes) with the necessary combination of (1) redox potentials that ...exceed the potential limits of water, (2) high solubility in nonaqueous media, and (3) high stability toward electrochemical cycling. In addition, ideal materials would maintain all three of these properties over multiple electron transfer events, thereby providing a proportional increase in storage capacity. This paper describes the mechanism-based design of a new class of metal-coordination complexes (MCCs) as anolytes for NRFBs. The tridentate bipyridylimino isoindoline (BPI) ligands of these complexes were designed to enable multielectron redox events. These molecules were optimized using a combination of systematic variation of the BPI ligand and the metal center along with mechanistic investigations of the decomposition pathways that occur during electrochemical cycling. Ultimately, these studies led to the identification of nickel BPI complexes that could undergo stable charge-discharge cycling (<5% capacity loss over 200 cycles) as well as a derivative that possesses the previously unprecedented combination of high solubility (>700 mM in CH3CN), multiple electron transfers at low redox potentials (–1.7 and –1.9 V versus Ag/Ag+), and high stability in the charged state for days at high concentration. Overall, the studies described herein have enabled the identification of a promising anolyte candidate for NRFBs and have also provided key insights into chemical design principles for future classes of MCC-based anolytes.
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•Acid-base properties of Mo2N correlate to presence of nitrogen and oxygen sites.•Pretreatment conditions impact the density and nature of acid-base sites on Mo2N.•Basic activity of ...passivated Mo2N increases with H2 reduction and renitridation.•Base site density and basic character of Mo2N is suppressed by passivation.•Acid character of Mo2N decreased proportionately with increasing basic properties.
The presence of nitrogen and oxygen sites was shown to have a direct impact on the acid-base properties of Mo2N. The gas phase reaction of 2-methyl-3-butyn-2-ol (MBOH), temperature programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS) were used to characterize the Mo2N catalyst. The acid-base character of Mo2N was impacted by synthesis and surface pretreatment methods prior to analysis. The basic character of passivated Mo2N increased after the following pretreatment: degassing in helium < reduction in hydrogen < in-situ unpassivated < renitridation. The CO2 desorbed during TPD increased from 0 to 128.8 × 1016 molecules/m2 for the degassed and renitrided Mo2N, while NH3 desorption decreased from 134 to 13.2 × 1016 molecules/m2, respectively. Acid-base character was linked to N/O atomic ratio using XPS. The renitrided Mo2N surface exhibited the highest N/O atomic ratio, base site density, highest acetylene selectivity, while displaying the lowest acid site density and activity.
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► Capacitances in excess of 200Fg−1 for phase-pure VN and γ-Mo2N in KOH and H2SO4, respectively. ► Electrolyte ion isolation experiments used to identify key contributors to charge ...storage. ► Ion isolation results unambiguously link OH− and H+ to pseudocapacitance for VN/KOH and Mo2N/H2SO4, respectively.
Phase pure, nanostructured V, Mo and W nitrides and carbides were synthesized and characterized in aqueous KOH and H2SO4 electrolytes. Capacitances for most of the materials exceeded that expected for double layer charging and suggested a pseudocapacitive storage mechanism. With the exception of β-Mo2C, the materials were stable in KOH and/or H2SO4 electrolytes. Capacitances for VN in KOH and γ-Mo2N in H2SO4 were the highest and exceeded 200Fg−1. The charge-storage species were interrogated using an ion isolation method. The results provide unambiguous evidence that OH− was the principal charge storage species responsible for the pseudocapacitance demonstrated for VN in KOH while H+ was the principal species for γ-Mo2N in H2SO4.
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