As one of the most promising photocatalysts, TiO 2 suffers from disadvantages of a wide band gap energy and especially the ultrafast recombination of photoinduced-charges, which limit its practical application for efficient solar water splitting. Here we show a hitherto unreported carbon/TiO 2 /carbon nanotube (CTCNT) composite featuring a TiO 2 nanotube sandwiched between two thin tubes of carbon with graphitic characteristics. The carbon layer is only about 1 nm thick covering the surface of TiO 2 nanotubes. The minimum bandgap between the edges of band tails for the CTCNTs can conjecturally be narrowed to 0.88 eV, and the measured apparent quantum efficiency of CTCNT in the ultraviolet light region is even close to 100%, indicating it can greatly enhance the utilization of sunlight and extremely suppress charge recombination. As a consequence, under illumination of one AM 1.5G sunlight, CTCNT can give a superhigh solar-driven hydrogen production rate (37.6 mmol h À1 g À1 ), which is much greater than the best yields ever reported for TiO 2 -based photocatalysts. We anticipate this work may open up new insights into the architectural design of nanostructured photocatalysts for effective capture and conversion of sunlight. Broader contextSolar-driven water-splitting into H 2 and O 2 is recognized as a promising clean, sustainable way to overcome the limited supply of fossil fuels and the greenhouse effect. This requires that photocatalysts effectively harvest sunlight and simultaneously drive the photoreaction with high quantum efficiency. The rational design of efficient catalysts for water splitting is one of the major challenges in recent years. In this work, we show a hitherto unreported carbon/TiO 2 /carbon nanotube structure (CTCNT) that features in a TiO 2 nanotube sandwiched between two thin tubes of graphitic carbon. This unique construction endows the CTCNT material with a minimum bandgap narrowing to 0.88 eV and an excellent apparent quantum efficiency of nearly 100% in the ultraviolet light region. As the result, a super-high solar-driven hydrogen production rate (37.6 mmol h À1 g À1 ) can be given by the CTCNT material, indicating it can greatly enhance the utilization of sunlight and extremely suppress the charge recombination. We anticipate this work may open up new insights to improve the photocatalytic conversion efficiency in solar-driven reactions.
Mg-Al hydrotalcites with different Mg/Al molar ratios were prepared and characterized by XRD, FT-IR, SEM and BET analyses. The calcined hydrotalcite with Mg/Al molar ratio of 4.0 (LDO Mg/Al 4.0) exhibited the highest catalytic activity in the synthesis of propylene glycol methyl ether (PM). The catalytic activity relating to the amount of the basic sites and crystallinity depended on the Mg/Al molar ratio. The optimal equilibrium of acidbase property and high crystallinity made the LDO Mg/Al 4.0 an excellent catalyst in the reaction. Etherification of propylene oxide (PO) with methanol over the LDO Mg/Al 4.0 was researched. The optimized reaction conditions were as follows: 140°C, catalyst amount 0.9 wt%, methanol/PO molar ratio 4.0 and 6 h. The PO conversion and PM selectivity were 93.2 and 97.4%, respectively. Above all, almost all the PM was 1-methoxy-2-propanol, for no 2-methoxy-1-propanol was detected by GC analysis in the reaction products, and the catalyst could be reused for five times.
Different kinds of activated carbon‐ and carbon nanotube‐supported palladium catalysts were investigated in the selective hydrogenation of nitrocyclohexane to cyclohexanone oxime under mild conditions. Carbon nanotube‐supported palladium catalysts demonstrate better catalytic performance than activated carbon‐supported palladium catalysts in general because of their mesoporous structures, which are favorable supports for the accessibility of the reactants to the active sites and the product desorption from the catalyst. Hydrogen chemisorption, transmission electron microscopy and X‐ray photoelectron spectroscopy indicate that higher composition of Pd+ on the catalyst surface, larger palladium surface area, and better palladium dispersion contribute to an increase in the activity and selectivity toward cyclohexanone oxime. In addition, single‐wall carbon nanotube‐supported palladium catalysts give the best result of 97.7 % conversion of nitrocyclohexane and 97.4 % selectivity toward cyclohexanone oxime. On the basis of the results of GC–MS and the designed experiments, a possible reaction scheme was proposed.
Developing a new environmentally friendly process for benzene nitration to nitrobenzene has been highly desirable for a long time. In this work, NO 2 was used as a nitration agent to replace traditional nitric acid, and different mesoporous SiO 2 and their supported heteropoly acid (salt) were employed to catalyze benzene nitration to nitrobenzene. Several typical catalysts were characterized using XRD, BET and FT-IR, and the acid amounts of the various catalysts were determined. The effects of various factors such as different catalysts, the molar ratio of benzene to NO 2 , reaction temperature, reaction time, HPW loading, the acid amounts of the catalyst and the reuse of the catalyst on the nitration reaction have also been systematically examined. The results indicate that the supported HPW/MCM-41 catalysts exhibit a remarkably synergistic catalytic performance on the nitration reaction of benzene to nitrobenzene. In particular, the 50%HPW/MCM-41 catalyst gives the best results with 73.4% benzene conversion and 98.8% selectivity to nitrobenzene under the optimal reaction conditions. Moreover, the mesoporous structure of MCM-41 was retained under the high loading of HPW. The possible reaction mechanism for the nitration reaction of benzene with NO 2 over HPW/MCM-41 is suggested in the present work. This method provides a promising strategy for the preparation of nitro-aromatic compounds from a catalytic nitration reaction by using NO 2 as the nitration reagent.
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