Anjie Wang

Hydrothermal Synthesis of Ionic Liquid [Bmim]OH-Modified TiO2 Nanoparticles with Enhanced Photocatalytic Activity under Visible Light

TiO(2) nanocomposites modified with the ionic liquid [Bmim]OH are synthesized by a hydrothermal procedure. X-ray diffraction, Zeta-potential measurement, TEM, thermogravimetric analysis, photoluminescence, UV/Vis, FTIR, and X-ray photoelectron spectroscopy are used to characterize the TiO(2) nanocomposites. The TiO(2) nanocomposites consist of pure anatase particles of about 10 nm. The modification of [Bmim]OH on the surface of the TiO(2) particles extends the TiO(2) absorption edge to the visible-light region. The electrochemical redox potentials indicated that the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of [Bmim]OH match well with the valence band (VB) and conduction band (CB) of the TiO(2) semiconductor. [Bmim]OH-modified TiO(2) is much more active than pristine TiO(2) under visible-light irradiation in the photocatalytic degradation of methylene blue in aqueous solution. [Bmim]OH is chemically bonded to the surface Ti-OH of TiO(2) particles rather than adsorbed on the surface. A possible mechanism for the photocatalysis is proposed.

Effect of surface proton exchange on hydrodesulfurization performance of MCM-41-supported catalysts

Abstract Ni-Mo, Co-Mo, Ni-W and Pt were supported over siliceous MCM-41 (Si-MCM-41) or the proton-exchanged Si-MCM-41 (H + -MCM-41) in order to investigate the effect of support surface modification on the performance of the catalysts. The prepared catalysts were evaluated by the hydrodesulfurization (HDS) of dibenzothiophene (DBT). It is indicated that the supported Ni-Mo sulfides exhibited the highest HDS activity regardless of the support, and that Ni-W sulfides showed the highest hydrogenation activity. The H + -MCM-41-supported Ni-Mo, Ni-W or Pt catalyst performed much better in HDS of DBT than the Si-MCM-41-supported counterpart. From the relative selectivity of cyclohexylbenzene (CHB) to biphenyl (BP) ( S CHB / S BP ), it could be concluded that the higher HDS performance of H + -MCM-41-supported catalysts may be attributed to the enhanced hydrogenation activity. Nevertheless, a little difference in HDS activity was observed for Co-Mo sulfides supported on Si-MCM-41 or H + -MCM-41. Since the cleavage of sulfur atoms mainly takes the route of hydrogenolysis in HDS of DBT catalyzed by Co-Mo sulfides, the improvement in hydrogenation activity was not significant for Co-Mo sulfides when Si-MCM-41 was ion-exchanged with HNO 3 . TPR study showed that the profiles of Ni-Mo/Si-MCM-41 and Ni-W/Si-MCM-41 changed markedly after the proton exchange of Si-MCM-41 while the profile of Co-Mo/Si-MCM-41 changed a little. It may be concluded that the removal of sulfur from DBT and hydrogenation take place on separate active sites, and that the spillover of the dissociated hydrogen species over the surface is essential to the hydrogenation pathway. Hydroxyl groups on H + -MCM-41 favors the spillover of the hydrogen species, enhancing the hydrogenation activity of its supported catalysts. On the other hand, Na + cations on Si-MCM-41 may “trap” the spillover hydrogen species, lowering the hydrogenation activity of its supported catalysts.

Effects of precipitation aging time on the performance of CuO/ZnO/CeO2-ZrO2 for methanol steam reforming

Abstract CuO/ZnO/CeO 2 -ZrO 2 catalysts for methanol steam reforming (MSR) were prepared by a co-precipitation procedure, and the effects of precipitation aging time on the catalytic performance were investigated. It was found that the prolonged precipitation aging time increased the surface Cu atoms and improved the reducibility of catalyst, but decreased the oxygen storage capacity. A nearly linear increase between the surface Cu atoms and H 2 production rate was obtained in prepared CuO/ZnO/CeO 2 -ZrO 2 catalysts with prolonged precipitation aging time. However, CO concentration increased with the decrease of the oxygen storage capacity. Considering the H 2 production rate and CO level, the optimal precipitation aging time was 2 h. CuO/ZnO/CeO 2 -ZrO 2 prepared using this aging time exhibited the best activity with suppressed CO formation.

Hydrodesulfurization of Dibenzothiophene Over Ni-Mo Sulfides Supported by Proton-Exchanged Siliceous MCM-41

Strong acid sites on the surface of mesoporous MCM-41 were generated by ion-exchanging siliceous MCM-41 with dilute HNO3 solution (0.5 M). The XRF determination indicates that most of the sodium cations contained in MCM-41 can be removed by the proton exchange, and dealuminization was observed during the proton exchange. The acidity of the mesoporous materials was characterized by means of NH3-TPD and the Hammett indicators. It is revealed that new strong acid sites (-5.6 > H0 > -8.2) were generated after the first 2 h of ion exchange and that the following ion exchanges had little effect on the acidic properties. XRD patterns of the mesoporous materials indicate that the structure of siliceous MCM-41 was improved by HNO3 ion exchange. When Ni-Mo sulfides were supported on the prepared solid acid (H+-MCM-41), high performance in the hydrodesulfurization (HDS) of dibenzothiophene (DBT) was observed. However, the HDS activity was decreased while the selectivity of biphenyl (BP) was increased, when H+-Si-MCM-41 was ion exchanged with Na2CO3 aqueous solution. TPR profiles of the supported Ni-Mo oxides reveal that the acidic properties of the supports greatly influence the hydrogenation activities of the bimetallic oxides. The high performance of H+-MCM-41-supported Ni-Mo catalysts may be attributed to the enhanced hydrogenation activity. The introduction of Na cation into the support led to the decrease of the HDS activity due to the poor hydrogenation ability of the supported bimetallic oxides. The HDS activity is well correlated with the low H2 consumption temperature in the TPR profiles.

Phase Effect of NixPy Hybridized with g-C3N4 for Photocatalytic Hydrogen Generation

The use of noble metal-free nickel phosphides (NixPy) as suitable cocatalysts in photocatalytic hydrogen (H2) generation has gained a lot of interest. In this paper, for the first time, three different crystalline phases of nickel phosphides, Ni2P, Ni12P5, and Ni3P, were synthesized and then hybridized with g-C3N4 to investigate the phase effect of NixPy on photocatalytic H2 generation. It has been found that all three phases of NixPy work as effective cocatalysts for the enhancement of visible light H2 generation with g-C3N4. The effective charge transfer between g-C3N4 and NixPy, demonstrated by photoelectrochemical properties, photoluminescence, and time-resolved diffused reflectance, contributes to the enhanced photocatalytic H2 generation performance. Interestingly, Ni2P/g-C3N4 showed the highest photocatalytic activity among the three NixPy/g-C3N4. NixPy with a higher ratio of phosphorus (Ni2P) can accelerate charge transfer and provide more Ni-P bonds, leading to a preferable H2 generation performance.

Performance of NiMoS/Al2O3 prepared by sonochemical and chemical vapor deposition methods in the hydrodesulfurization of dibenzothiophene and 4,6-dimethyldibenzothiophene

Different types of NiMoS/Al2O3 catalysts were prepared by a combination of sonochemical synthesis and chemical vapor deposition (CVD) methods. The performance of the prepared catalysts in the hydrodesulfurization (HDS) of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) was compared with that of catalysts prepared using the impregnation method. Ni that was selectively added to the MoS2 surface by CVD promoted the HDS activity to a greater extent than Ni added by impregnation, particularly for the direct-desulfurization (DDS) route of the reaction. This was attributed to the former method allowing an intimate interaction between the added Ni and the MoS2 surface, as confirmed by the XPS analysis of the catalysts. NiMoS/Al2O3 prepared by a combination of two methods, sonochemical and CVD, showed improvement in activity over the catalyst prepared by impregnation. Moreover, the hydrogenation (HYD) activity of the former catalyst was significantly higher than that of the latter due to the dominant effect of sonochemical synthesis on the activity. The improvement in activity was greater for the HDS of 4,6-DMDBT than for the HDS of DBT.

Decomposition of hydrogen sulfide in non-thermal plasma aided by supported CdS and ZnS semiconductors

The decomposition of hydrogen sulfide (H2S) has attracted increasing attention because it produces hydrogen from a hazardous waste gas. However, the thermal equilibrium limitation in the decomposition gives rise to low H2S conversion and high energy costs for hydrogen production. In the present work, we demonstrate that alumina-supported CdS and ZnS significantly enhanced the conversion in the non-thermal plasma-induced decomposition of H2S, achieving full conversion at reasonably low energy consumption. It appears that the enhancement might be attributed to the conversion of H2S by its reaction with h+ and e− on the surface of the CdS and ZnS semiconductors, which are generated by the strong electric field and plasma-induced photons.

Synthesis of highly dispersed metal sulfide catalysts via low temperature sulfidation in dielectric barrier discharge plasma

A new strategy is reported for the synthesis of supported metal sulfides with high dispersion by sulfidation in dielectric barrier discharge (DBD) plasma under ambient conditions. According to the characterization data obtained by XRD, BET, UV-vis, TEM, XPS, ICP, and elemental analysis, the DBD plasma method not only reduces the preparation time but also achieves an increased dispersion, small particle size and uniform distribution compared to the traditional thermal method. These results prove that the plasma preparation method is a facile and flexible approach for the synthesis of metal sulfides. The plasma-prepared CdS/Al2O3 and ZnS/Al2O3 catalysts exhibited high performances for hydrogen production from H2S with reduced energy costs. The enhancement might be attributable to the smaller particle size, higher surface area and dispersion, which enhances the semiconductor catalytic efficiency.

Hydrodesulfurization of dibenzothiophene and 4,6-dimethyldibenzothiophene over Ni-Mo catalysts supported by siliceous SBA-15

A deep hydrodesulfurization (HDS) catalyst, which was considerably active to desulfurize dibenzothiophene (DBT) and 4, 6-dimethyldibenzothiophene (4,6-DMDBT), was prepared by depositing Ni-Mo species over SBA-15. The extremely high surface area of SBA-15 favors the dispersion of the active species, which result in very high HDS activity. The optimal Ni/Mo atomic ratio for this series of catalysts is 0.25. Ni-Mo(0.25)/SBA-15 exhibited excellent performance in HDS of DBT and 4,6-DMDBT.

Ni3P as a high-performance catalytic phase for the hydrodeoxygenation of phenolic compounds

The catalytic performance of an unsupported Ni2P in the aqueous phase hydrodeoxygenation (HDO) of phenol was investigated. It was found that the unsupported Ni2P was water-sensitive, being transformed stepwise, first to an amorphous phase and then to Ni5P2 and Ni12P5, and finally to Ni3P in the presence of water at elevated temperatures. Nonetheless, the generated Ni3P phase exhibited extraordinary hydrogenation activity at low temperatures and high HDO activity at high temperatures. The unsupported Ni3P was more active for the hydrogenation of the aromatic ring in the phenol molecule than Pd/SiO2 (1.0 wt%). The unsupported Ni3P was catalytically active and stable in phenol HDO in both the aqueous phase and the organic phase. In addition to phenol, catechol and o-cresol were investigated in the HDO catalyzed by the unsupported Ni3P in both aqueous solution and decalin solution. The HDO reactivity decreased in the order of phenol > catechol > o-cresol in the aqueous phase, and in the order of phenol > o-cresol in the organic phase (catechol is insoluble in decalin). In the oil phase HDOs of phenol and o-cresol, the unsupported Ni3P exhibited superior hydrogenation activity to that of the unsupported Ni2P at low temperatures.