Rational use of abundant natural gas is gaining importance as petroleum oil reserves are diminishing. Methane, the main component of natural gas, can be converted to liquid fuels, hydrogen, and other value-added chemicals through a syngas intermediate, a mixture of CO and H 2 . Currently, syngas is produced by reacting methane with steam at high temperatures and pressures. This process is very energy-and capitalintensive, as the reaction is highly endothermic. An alternative process to produce syngas is the partial oxidation of methane (POM) with pure oxygen in the presence of a catalyst. [1,2] The exothermic nature of POM makes the process attractive in terms of energy consumption. The other advantage of POM over the steam-reforming process is that the H 2 /CO ratio of~2 of the as-produced syngas is highly suitable for subsequent conversion to environmentally friendly liquid fuels through a Fischer-Tropsch process. The main difficulty with POM lies in the consumption of large quantities of expensive pure oxygen that is produced by the cryogenic separation of air. A recent development in syngas production technology is the use of oxygen-permeable dense ceramic membranes [3,4] integrating the oxygen separation and POM processes in a single space.[5] The formidable problem for this approach is that the membrane must be chemically and mechanically stable at elevated temperatures in a large oxygen gradient with one side of the membrane exposed to oxidizing atmosphere (air) and the other side to the reducing atmosphere (the mixture of hydrogen and carbon monoxide). Herein we propose a two-stage membrane reactor, as depicted in Figure 1 a, which may reduce the requirement on the stability of the membrane materials. In this reactor, part of the methane is converted into CO 2 and H 2 O by reaction with oxygen permeated through the membrane from the air, and the resultant mixture is transferred to a catalyst bed where the remaining methane is reformed to syngas.A ceramic composite of Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3Àd (97.5 mol %) and Co 3 O 4 (2.5 mol %) was used to construct a membrane reactor. The major phase of the composite was intended for separating oxygen from air [6] and the minor phase at the surface for catalyzing the reaction of methane with permeated oxygen; [7] in terms of mechanics, small cobalt oxide particles embedded in the bulk may also reinforce the major phase. The dense tubular membrane of the required phase composition was prepared by extrusion followed by sintering at 1100 8C for 10 h. A g-Al 2 O 3 -supported catalyst was prepared with a nickel loading of 12.5 wt % and sieved to 40~60 mesh.[8] The reactor consisted of a membrane of length 2.14 cm, inner diameter 0.76 cm (membrane surface area 5.10 cm 2 ), and wall thickness 0.13 cm, and a catalyst bed containing 0.2 g Ni/g-Al 2 O 3 ; the membrane tube and the catalyst bed were separated by a distance of 2.5 cm (see Figure 1 b). In order to improve the flow pattern in the reactor, an alumina cylinder was placed inside the reactor (not shown in Figure...

Rational use of abundant natural gas is gaining importance as petroleum oil reserves are diminishing. Methane, the main component of natural gas, can be converted to liquid fuels, hydrogen, and other value-added chemicals through a syngas intermediate, a mixture of CO and H 2 . Currently, syngas is produced by reacting methane with steam at high temperatures and pressures. This process is very energy-and capitalintensive, as the reaction is highly endothermic. An alternative process to produce syngas is the partial oxidation of methane (POM) with pure oxygen in the presence of a catalyst. [1,2] The exothermic nature of POM makes the process attractive in terms of energy consumption. The other advantage of POM over the steam-reforming process is that the H 2 /CO ratio of~2 of the as-produced syngas is highly suitable for subsequent conversion to environmentally friendly liquid fuels through a Fischer-Tropsch process. The main difficulty with POM lies in the consumption of large quantities of expensive pure oxygen that is produced by the cryogenic separation of air. A recent development in syngas production technology is the use of oxygen-permeable dense ceramic membranes [3,4] integrating the oxygen separation and POM processes in a single space.[5] The formidable problem for this approach is that the membrane must be chemically and mechanically stable at elevated temperatures in a large oxygen gradient with one side of the membrane exposed to oxidizing atmosphere (air) and the other side to the reducing atmosphere (the mixture of hydrogen and carbon monoxide). Herein we propose a two-stage membrane reactor, as depicted in Figure 1 a, which may reduce the requirement on the stability of the membrane materials. In this reactor, part of the methane is converted into CO 2 and H 2 O by reaction with oxygen permeated through the membrane from the air, and the resultant mixture is transferred to a catalyst bed where the remaining methane is reformed to syngas.A ceramic composite of Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3Àd (97.5 mol %) and Co 3 O 4 (2.5 mol %) was used to construct a membrane reactor. The major phase of the composite was intended for separating oxygen from air [6] and the minor phase at the surface for catalyzing the reaction of methane with permeated oxygen; [7] in terms of mechanics, small cobalt oxide particles embedded in the bulk may also reinforce the major phase. The dense tubular membrane of the required phase composition was prepared by extrusion followed by sintering at 1100 8C for 10 h. A g-Al 2 O 3 -supported catalyst was prepared with a nickel loading of 12.5 wt % and sieved to 40~60 mesh.[8] The reactor consisted of a membrane of length 2.14 cm, inner diameter 0.76 cm (membrane surface area 5.10 cm 2 ), and wall thickness 0.13 cm, and a catalyst bed containing 0.2 g Ni/g-Al 2 O 3 ; the membrane tube and the catalyst bed were separated by a distance of 2.5 cm (see Figure 1 b). In order to improve the flow pattern in the reactor, an alumina cylinder was placed inside the reactor (not shown in Figure...

Reduction of bare carbon dots (CDs) in aqueous NaBH(4) solution is a facile and effective approach to enhance their fluorescence without any surface coverage. CDs are treated with dilute aqueous NaBH(4) solutions, enhancing their quantum yields (QYs) successfully from 1.6 % to 16 % which is comparable to semiconductive QDs in aqueous environments. If pristine CDs are treated hydrothermally prior to reduction by NaBH(4), QYs reach 40.5 %. This value is among the highest QYs reported for bare CDs in the literature. The approach to enhance fluorescence through chemical reduction is generally applicable to other kinds of CDs synthesized by various methods. Alteration of the chemical structure of the CDs by NaBH(4)-reduction is analyzed by (13) C NMR, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy, which demonstrate that the carbonyl group content is decreased after NaBH(4)-reduction, whereas the number of sp(3)-type carbon defects is increased. The valence-band maxima (VBM) near the surface related to the surface energy bands of the CDs are estimated by XPS. VBM data show a semiconducting layer on the surface of the CDs, and the VBM of the CDs decrease with increasing NaBH(4)-reduction time. The layered graphite structures in the cores of the CDs are clearly observed by transmission electron microscopy (TEM). CDs could perhaps be regarded as semiconductive surface defect layers formed by chemical erosion over conductive graphite cores. Chemical reduction by NaBH(4) changes the surface-energy bands of the CDs, thus, enhances their fluorescence. The fluorescence properties of aqueous NaBH(4)-reduced CDs are also studied for possible biological applications.

We used a click reaction to synthesize a bidentate 1,2,3-triazole-based ligand, TA, for use in the preparation of aqueous CdS quantum dots (QDs). TA-conjugated CdS QDs exhibited two fluorescence emission peaks, one at 540 nm arising from CdS nanocrystals and the other at approximately 670 nm arising from TA-CdS QD complexes formed via surface coordination. Coordination between TA and CdS was verified by using X-ray photoelectron (N 1s) spectra as well as Raman and NMR spectra of TA-capped QDs. Electrochemical analysis revealed that the 1,2,3-triazole moities in TA form complexes with the Cd(II) ions. The aqueous QDs protected by TA were very stable at different ionic strengths and over a broad pH range, according to fluorescence analysis. The ethidium bromide exclusion assay demonstrated that the bidentate TA ligand interacts strongly with DNA. Fluorescent micrographs and TEM images of cancer cells stained with TA-capped QDs clearly showed that the TA ligand targeted CdS QDs to the nucleoli of cells. In contrast, thioglycolic acid-capped CdS QDs just stained the cell membranes and could not pass the cell membranes to reach the cell nucleus.

Partial oxidation of methane to synthesis gas was investigated in a reactor consisting of an oxygen-permeable SrFeCo 0.5 O y membrane tube and a Ni/γ-Al 2 O 3 catalyst bed located after the membrane tube. In this reactor, part of methane reacted with oxygen that permeated through the membrane from air, and the resultants (H 2 O, CO 2 ) and the rest of methane were transported to the catalyst bed where they were converted to syngas. When a reactor of membrane surface area 4.6 cm 2 was run at 900 °C with a methane feeding rate of 26.8 mL/min, the throughput conversion of methane was ∼98%, the CO selectivity ∼98%, H 2 /CO ∼1.8, syngas generation rate 16 mL/min/cm 2 . Under the reactor conditions, the layered phase Sr 4 (Fe,Co) 6 O 13 in the membrane gradually decomposed to a perovskite phase SrFe 1-x Co x O 3-δ with high oxygen permeability and spinel phase [(CoFe)] 2 CoO 4 with catalytic activity toward the oxidation of methane. The Ni-based reforming catalyst exhibited desirable activity and stability in the membrane reactor, which may be attributed to the absence of the "hot spots" in the catalyst.