[Show abstract][Hide abstract] ABSTRACT: Knowledge of the relationship between gas solubility and enthalpy change of chemical absorption of CO2 is very important for exploring energy-efficient absorbents for CO2 capture. To this end, equations that can directly correlate gas solubility with absorption enthalpy were derived through combining the van’t Hoff Equation with the Reaction Equilibrium Thermodynamic Model (RETM). Two typical reaction mechanisms for chemical absorption of CO2 (1:1 and 1:2) were considered for RETM. The variations of gas solubility with enthalpy change were found to be distinctively sigmoid functions, regardless of the investigated temperature and pressure or assumed reaction forms between CO2 and the absorbent molecule. Theoretically calculated variation curves of gas solubility vs. enthalpy change agreed well with experimental results reported in literature. Based on the trade-off relationship between gas solubility and enthalpy change, criterions for evaluating energy-efficient chemical absorbents for CO2 capture were proposed.
[Show abstract][Hide abstract] ABSTRACT: High-surface-area nanosized CeO2 and M-doped CeO2 (M=Cu, La, Zr, and Mg) prepared by a surfactant-templated method were tested for CO2 adsorption. Cu, La, and Zr are doped into the lattice of CeO2 , whereas Mg is dispersed on the CeO2 surface. The doping of Cu and La into CeO2 leads to an increase of the CO2 adsorption capacity, whereas the doping of Zr has little or no effect. The addition of Mg causes a decrease of the CO2 adsorption capacity at a low Mg content and a gradual increase at a higher content. The CO2 adsorption capacity follows the sequence Cu-CeO2 >La-CeO2 >Zr-CeO2 ≈CeO2 >Mg-CeO2 at low dopant contents, in line with the relative amount of defect sites in the samples. It is the defect sites on the surface, not in the bulk of CeO2 , modified by the dopants that play the vital role in CO2 chemisorption. The role of surface oxygen vacancies is further supported by an in situ IR spectroscopic study of the surface chemistry during CO2 adsorption on the doped CeO2 .
[Show abstract][Hide abstract] ABSTRACT: Platinum group metal (PGM) catalysts are the current standard for control of pollutants in automotive exhaust streams. Aside from their high cost, PGM catalysts struggle with CO oxidation at low temperatures (<200 °C) due to inhibition by hydrocarbons in exhaust streams. Here we present a ternary mixed oxide catalyst composed of copper oxide, cobalt oxide, and ceria (dubbed CCC) that outperforms synthesized and commercial PGM catalysts for CO oxidation in simulated exhaust streams while showing no signs of inhibition by propene. Diffuse reflectance IR (DRIFTS) and light-off data both indicate low interaction between propene and the CO oxidation active site on this catalyst, and a separation of adsorption sites is proposed as the cause of this inhibition resistance. This catalyst shows great potential as a low-cost component for low temperature exhaust streams that are expected to be a characteristic of future automotive systems.
Angewandte Chemie International Edition 09/2015; DOI:10.1002/anie.201506093 · 11.26 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A high-surface-area polyethylene-fiber adsorbent (AF160-2) has been developed at the Oak Ridge National Laboratory by radiation-induced graft polymerization of acrylonitrile and itaconic acid. The grafted nitriles were converted to amidoxime groups by treating with hydroxylamine. The amidoximated adsorbents were then conditioned with potassium hydroxide (KOH) by varying different reaction parameters such as KOH concentration (0.2, 0.44, and 0.6 M), duration (1, 2, and 3 h), and temperature (60, 70, and 80 °C). Adsorbent screening was then performed with simulated seawater solutions containing sodium chloride and sodium bicarbonate, at concentrations found in seawater, and uranium nitrate at a uranium concentration of ∼7–8 ppm and pH 8. Fourier transform infrared spectroscopy and solid-state NMR analyses indicated that a fraction of amidoxime groups was hydrolyzed to carboxylate during KOH conditioning. The uranium adsorption capacity in the simulated seawater screening solution gradually increased with conditioning time and temperature for all KOH concentrations. It was also observed that the adsorption capacity increased with an increase in concentration of KOH for all the conditioning times and temperatures. AF160-2 adsorbent samples were also tested with natural seawater using flow-through experiments to determine uranium adsorption capacity with varying KOH conditioning time and temperature. Based on uranium loading capacity values of several AF160-2 samples, it was observed that changing KOH conditioning time from 3 to 1 h at 60, 70, and 80 °C resulted in an increase of the uranium loading capacity in seawater, which did not follow the trend found in laboratory screening with stimulated solutions. Longer KOH conditioning times lead to significantly higher uptake of divalent metal ions, such as calcium and magnesium, which is a result of amidoxime conversion into less selective carboxylate. Scanning electron microscopy showed that long conditioning times may also lead to adsorbent degradation.
[Show abstract][Hide abstract] ABSTRACT: The importance of porous carbon as the support material is well recognized in the catalysis community, and it would be even more attractive if several characteristics are considered, such as the stability in acidic and basic media or the ease of noble metal recovery through complete burn off. Because it is still difficult to obtain constant properties even from batch to batch, activated carbons are not popular in industrial catalysis now. During the past decade, the rapid development of nanotechnology has boosted the carbon field, and a number of novel carbons with unique morphologies (such as carbon nanospheres, graphene or sheet-like carbon, and ordered mesoporous carbon) and composites (such as nitrogen-doped carbon and carbon nitride) are emerging, which at the same time greatly benefit heterogeneous catalysis. Metal nanoparticles or metal oxides supported on those carbon supports resulted in interesting and exceptional performances in various catalytic processes, such as selective oxidations, hydrogenations, and oxygen reduction reactions. In this contribution, we review recent progress of porous carbon supports with different morphologies and compositions.
[Show abstract][Hide abstract] ABSTRACT: Rare-earth elements provide the cornerstones to clean sustainable energy and modern technologies such as computers, communications, and transportation. As such, the recovery of rare earths (REs) from minerals such as bastnaesite remains important for modern times. As the light lanthanides (La–Nd) constitute the majority (typically >98.7 %) of the REs in bastnaesite with the heavy REs (Sm–Lu) contributing the remainder (approximately 1.3 %), an enrichment of heavier REs may serve as an effective means of assisting rare-earth recovery. Such an extractive metallurgy process involving ionic liquids (ILs) leads to an enrichment of heavy REs by nearly an order of magnitude. The acidic IL N,N-dimethylacetamidium bis(trifluoromethylsulfonyl)imide (DMAH+NTf2–) in the IL 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIM+NTf2–) dissolves froth flotation bastnaesite, synthetic bastnaesite analogues (RECO3F), RE2O3, and RE2(CO3)3 minerals. An overall reaction for the dissolution of bastnaesite is proposed for this IL system. This IL system may provide the initial stages of a greater RE separation scheme for bastnaesite froth flotation concentrates.
Berichte der deutschen chemischen Gesellschaft 08/2015; 2015(26). DOI:10.1002/ejic.201500509 · 2.94 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We have studied the origin of the exchange bias effect in the Au-Fe3O4 dumbbell nanoparticles in two samples with different sizes of the Au seed nanoparticles (4.1 and 2.7 nm) and same size of Fe3O4 nanoparticles (9.8 nm). The magnetization, small-angle neutron-scattering, synchrotron x-ray diffraction, and scanning transmission electron microscope measurements determined the antiferromagnetic FeO wüstite phase within Fe3O4 nanoparticles, originating at the interface with the Au nanoparticles. The interface between antiferromagnetic FeO and ferrimagnetic Fe3O4 is giving rise to the exchange bias effect. The strength of the exchange bias fields depends on the interfacial area and lattice mismatch between both phases. We propose that the charge transfer from the Au nanoparticles is responsible for a partial reduction of the Fe3O4 into the FeO phase at the interface with Au nanoparticles. The Au-O bonds are formed, presumably across the interface to accommodate an excess of oxygen released during the reduction of magnetite.
[Show abstract][Hide abstract] ABSTRACT: Polymeric amines such as poly(ethyleneimine) supported on mesoporous oxides are promising candidate adsorbents for CO2 capture processes. An important aspect to the design and optimization of these materials is a fundamental understanding of how the properties of the oxide support such as pore structure, particle morphology, and surface properties affect the efficiency of the guest polymer in its interactions with CO2. Here, these issues are directly addressed via the preparation of an array of SBA-15 support materials with varying textural and morphological properties and with varying content of zirconium doped into the material. Zirconium is incorporated into the SBA-15 either during the synthesis of the SBA-15, or post-synthetically via deposition of Zr species on pre-synthesized SBA-15. It is found that the method of Zr incorporation altered the textural and morphological properties of the parent SBA-15 in different ways. Importantly, the CO2 capacity of SBA-15 impregnated with PEI increased with doped Zr for a 'standard' SBA-15 containing significant microporosity, while no increase in the CO2 capacity was observed upon Zr incorporation for an SBA-15 with improved textural properties. The collected data demonstrate that the textural and morphological properties of the support play a more significant role in impact the ability of PEI to capture CO2 than the support composition.
[Show abstract][Hide abstract] ABSTRACT: In this communication, we report a facile approach to constructing catalytic active hierarchical interfaces in 1-dimensional (1D) nanostructure, exemplified by the synthesis of TiO2-supported PtFe-FeOx nanowires (NWs). The hierarchical interface, constituting of atomic level interactions between PtFe and FeOx within each NW and the interactions between NWs and support (TiO2), enables CO oxidation with 100% conversion at room temperature. We identify the role of the two interfaces by probing the CO oxidation reaction with isotopic labeling experiments. Both the oxygen atoms (Os) in FeOx and TiO2 participate in the initial CO oxidation, facilitating the reaction through a redox pathway. Moreover, the intact 1D structure leads to the high stability of the catalyst. After 30 h in the reaction stream, the PtFe-FeOx/TiO2 catalyst exhibits no activity decay. Our results provide a general approach and new insights into the construction of hierarchical interfaces for advanced catalysis.
Journal of the American Chemical Society 08/2015; 137(32). DOI:10.1021/jacs.5b07011 · 12.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Graphene and graphene/metal oxide composite materials have attracted considerable interest for energy materials due to their excellent electrochemical performances. Here we propose using melamine as a template for the synthesis of cambered nano-walls of SnO2/rGO materials. Melamine powder can effectively absorb SnO2/GO from the solution to form a core-shell structure of melamine@SnO2/GO. After thermal reduction of GO at 200 oC to form the melamine@SnO2/rGO, melamine was dissolved in hot water at 80 oC, leaving behind the cambered SnO2/rGO nano-walls. Melamine is recyclable since it precipitates when its solution cools to room temperature. The thickness of the SnO2/rGO nano-walls can be easily controlled by adjusting the mass ratio of melamine to SnO2/GO. When the mass ratio was set to ten, cambered walls of SnO2/rGO with thickness of about 100-200 nm were achieved. The resulting SnO2/rGO delivered an initial reversible capacity of at 998 mAh/g at a current density of 100 mA/g and a capacity of 855 mAh/g after 100 discharge-charge cycles in a potential range between 0.02 and 3.0 V vs. Li/Li+. It also showed good rate performance with a reversible capacity of 460 mAh/g at 1A/g. These high capacities can be linked to the special cambered nano-walls which ensure fast solid diffusion in addition to providing an effective liquid-channel and buffer-volume in the electrode. The proposed synthesis method is easily scalable and should be applicable to many other graphene based energy materials.
[Show abstract][Hide abstract] ABSTRACT: A new kind of ionic liquid based on complexation of dipropyl sulfide (DPS) and AlCl3 has been prepared. The equivalent concentration of AlCl3 in the ionic liquid is as high as 2.3 M. More importantly, it is highly fluidic and exhibits an ambient ionic conductivity of 1.25 x 10-4 S cm-1. This new ionic liquid can be successfully used as an electrolyte for electrodeposition of aluminum.
Chemical Communications 07/2015; 51(68). DOI:10.1039/C5CC05233E · 6.83 Impact Factor