The creation of the magnetic and metallic characteristics in low-width MoS2 nanoribbon (1D MoS2): A DFT study

A basic understanding of the catalytic performance is needed to probe the physical properties that change with a reduction in the catalytic clusters size. It has been shown that the edge of low-width MoS₂ nanoribbon has a metallic characteristic, while that of bulk MoS₂ has a semi-conductive characteristic. For probing the observations, we constructed the models representing the surface atoms and the edge atoms of the MoS₂ nanoribbon. The nanoribbon-like model can also be used to model the edge atoms of the nanocluster MoS₂ .Then we calculated the density of states (DOS) of infinitely two-dimensional MoS₂ and of the structure corresponding to the edge atoms of the MoS₂ nanoribbon-like structure with Wien2K software. The magnetic moment of structures was calculated for identifying the magnetic structure. We found that the bulk MoS₂ and infinitely two-dimensional MoS₂ are semi-conductive and not magnetic, while the computation model corresponding to MoS₂ nanoribbon is metallic. The calculation anticipates that the edges of the MoS₂ nanocluster and the low-width MoS₂ nanoribbon are strongly magnetic.     

球状MoS2/WO3复合半导体制备及其对RhB的光催化性能

采用水热法成功制备了MoS₂/WO₃复合半导体光催化剂,分别通过SEM、TEM、EDS、XRD、Raman和DRS对催化剂的形貌,组成及结构进行表征,并用BET模型计算比表面积。对比发现球状MoS₂/WO₃对罗丹明B（RhB）的光降解效率明显高于纯WO₃、片状MoS₂/WO₃复合半导体。针对球状MoS₂/WO₃复合半导体,分别研究了MoS₂不同负载量（0.5%,1%,2%,5%,10%）对RhB光催化降解性能的影响,结果表明MoS₂含量为2%时催化效果最佳。同时,研究了溶液的pH值（pH=1,3,6,7,11）对光催化降解反应活性的影响,结果显示pH=6时降解率最高。当催化剂量增加到1 g·L^-1时,30min后RhB降解率达到96.6%。球状MoS₂/WO₃的瞬态光电流为0.050 6 mA·cm^-2,比纯WO₃提高了2.4倍。经过5次循环实验,球状MoS₂/WO₃复合半导体催化剂仍能保持90%的高降解率。     

球状MoS_2/WO_3复合半导体制备及其对RhB的光催化性能

采用水热法成功制备了MoS_2/WO3复合半导体光催化剂,分别通过SEM、TEM、EDS、XRD、Raman和DRS对催化剂的形貌,组成及结构进行表征,并用BET模型计算比表面积。对比发现球状MoS_2/WO3对罗丹明B(Rh B)的光降解效率明显高于纯WO3、片状MoS_2/WO3复合半导体。针对球状MoS_2/WO3复合半导体,分别研究了MoS_2不同负载量(0.5%,1%,2%,5%,10%)对Rh B光催化降解性能的影响,结果表明MoS_2含量为2%时催化效果最佳。同时,研究了溶液的p H值(p H=1,3,6,7,11)对光催化降解反应活性的影响,结果显示p H=6时降解率最高。当催化剂量增加到1 g·L-1时,30 min后Rh B降解率达到96.6%。球状MoS_2/WO3的瞬态光电流为0.050 6 m A·cm-2,比纯WO3提高了2.4倍。经过5次循环实验,球状MoS_2/WO3复合半导体催化剂仍能保持90%的高降解率。     

The Al2O3-Fe2O3 Mixed Oxidic System, II. Catalytic Decomposition of N2O

N₂O decomposition was examined over a series of Al₂O₃-Fe₂O₃ mixed oxidic solids with composition ranging from 0 to 100% of Fe₂O₃. The catalytic activity of the solids runs parallel to the number of atoms of iron in the Al_2−x Fe_xO₃ solid solution phase. Two compensation effects are present. The first corresponds to catalysts rich in alumina, and the second one to catalysts rich in hematite. This revised version was published online in June 2006 with corrections to the Cover Date.     

片状MoS2/MoS1.5Se0.5纳米复合材料的制备及其摩擦学性能研究

将钼粉与升华硫和硒粉的混合粉末按一定化学计量比混合,通过固相反应法成功制备出了均匀的片状纳米颗粒。分别使用X射线粉末衍射仪(XRD)、扫描电子显微镜(SEM)以及透射电子显微镜(TEM)对该纳米粉体进行结构表征和分析,发现该粉体为MoS2/MoS1.5Se0.5混合晶相,晶粒尺寸在300~600 nm,厚度约为5 nm的片状结构。将该MoS2/MoS1.5Se0.5纳米片作为润滑油添加剂添加到基础油中,使用UMT-2型摩擦磨损试验机对其摩擦学性能进行测试,并对摩擦机理进行了解释,结果表明MoS2/MoS1.5Se0.5纳米片作为润滑油添加剂具有良好的减摩抗磨性能。     

C/g-C3N4/MoS2复合材料的制备及光催化性能

首先以尿素和葡萄糖为前驱体,通过热缩合方法制备了C/g-C₃N₄,然后利用溶剂热法合成C/g-C₃N₄/MoS₂三元复合材料。通过不同的手段对其进行了表征,结果表明,与C/g-C₃N₄相比,该三元复合材料不仅具有更强的光吸收性能和更大的表面积,而且更有利于电子的转移。同时对其可见光催化降解甲基橙性能进行研究,结果发现,C/g-C₃N₄/MoS₂-2.0%复合材料(含有质量分数为2.0%的MoS₂)表现出最高的反应速率常数(0.0086 min^-1),分别为g-C₃N₄/MoS₂-2.0%(0.0015 min^-1)和C/g-C₃N₄(0.0036min^-1)的5.7倍和2.3倍。     

Solar hydrogen production. Significant effect of Na2CO3 addition on water splitting using simple oxide semiconductor photocatalysts

Recent progress in photocatalytic decomposition of water to H₂ and O₂ using simple oxide semiconductor catalysts has been reviewed. Addition of Na₂CO₃ to Pt/TiO₂ suspension in water enhanced the stoichiometric decomposition significantly. This Na₂CO₃ addition method has been proved to be very useful to accelerate water splitting over various kinds of oxide semiconductor photocatalysts. The role of CO₃ ^2– anion on the acceleration of water splitting was clarified. Finally, it was firstly demonstrated in the world that water was decomposed efficiently and stoichiometrically to H₂ and O₂ using a 3 wt% NiOx/TiO₂ photocatalyst under real solar light irradiation in Tsukuba, Japan by this Na₂CO₃ addition method.     

MoS_2/g-C_3N_4复合材料的制备及可见光催化性能

首先在N-甲基吡咯烷酮溶液中超声剥离得到少层的MoS_2,将其与石墨相氮化碳(g-C_3N_4)复合,制得MoS_2/g-C_3N_4复合材料。采用X射线衍射(XRD),扫描电镜(SEM),X射线光电子能谱(XPS),傅里叶变换红外光谱(FTIR),Raman光谱,紫外-可见漫反射吸收光谱(DRS)和光致荧光(PL)技术对复合材料进行表征。可见光下考察MoS_2/g-C_3N_4复合材料光催化降解罗丹明B(Rh B)的活性,结果表明:将少量MoS_2与g-C_3N_4复合可明显提高光催化活性,且1%(w/w)MoS_2/g-C_3N_4复合物的光催化活性最高,可能的原因是MoS_2和g-C_3N_4匹配的能带结构,增大了界面间电荷的传输,降低了光生电子-空穴的复合,进而提高了光催化活性。     

CrOx/SiO2催化剂上丙烷在CO2气氛中脱氢反应的研究

采用XRD、UV-vis DRS、ESR和微分吸附量热等技术,考察了铬担载量分别为2.5、5和10wt%的CrO_x/SiO₂催化剂的结构、表面性质和氧化还原性能。结果表明,催化剂表面上存在多种Cr的氧化态和聚集形式。随着Cr担载量从2.5wt%到10wt%的逐渐增大,催化剂表面占主导地位的Cr物种由CrO₃单体转为多聚CrO₃和Cr₂O₃晶相。在CO₂气氛中催化剂对丙烷转化率和丙烯选择性的大小顺序为2.5wt%CrO_x/SiO₂>5wt%CrO_x/SiO₂>10wt%CrO_x/SiO₂,反应过程中的原位ESR和UV-visDRS测定结果表明,催化剂表面的反应活性中心为Cr⁵⁺,Cr⁵⁺可由催化剂预处理过程中Cr³⁺的氧化及丙烷反应过程中CrO₃单体的还原产生,在反应中CO₂可使Cr³⁺重新氧化为Cr⁵⁺.     

Electronic Structures and Thermoelectric Properties of Two-Dimensional MoS2/MoSe2 Heterostructures

Thermoelectric properties of bulk and bilayer two-dimensional (2D) MoS₂/MoSe₂ heterostructures are investigated using density functional theory in conjunction with semiclassical Boltzmann transport theory. It is predicted that the bulk 2D heterostructures could considerably enhance the thermoelectric properties as compared with the bulk MoSe₂. The enhancement originates from the reduction in the band gap and the presence of interlayer van der Waals interactions. We therefore propose the 2D MoS₂/MoSe₂ heterostructures as a possible candidate material for thermoelectric applications.     

MoS2/g-C3N4复合材料的制备及可见光催化性能

首先在N-甲基吡咯烷酮溶液中超声剥离得到少层的MoS₂,将其与石墨相氮化碳（g-C₃N₄）复合,制得MoS₂/g-C₃N₄复合材料。采用X射线衍射（XRD）,扫描电镜（SEM）,X射线光电子能谱（XPS）,傅里叶变换红外光谱（FTIR）,Raman光谱,紫外-可见漫反射吸收光谱（DRS）和光致荧光（PL）技术对复合材料进行表征。可见光下考察MoS₂/g-C₃N₄复合材料光催化降解罗丹明B（RhB）的活性,结果表明：将少量MoS₂与g-C₃N₄复合可明显提高光催化活性,且1%（w/w）MoS₂/g-C₃N₄复合物的光催化活性最高,可能的原因是MoS₂和g-C₃N₄匹配的能带结构,增大了界面间电荷的传输,降低了光生电子-空穴的复合,进而提高了光催化活性。     

花瓣状微球MoS2/石墨烯复合材料的制备及其电化学性能

采用有利于二维层状结构形成的L-半胱氨酸作为硫源,钼酸钠作为钼源,制备聚乙烯基吡咯烷酮（PVP）辅助水热合成花瓣状微球形貌的MoS₂/还原氧化石墨烯复合电极材料（PVP-MoS₂/RGO）. X射线衍射（XRD）及透射电子显微镜（TEM）证实,经过PVP的适量添加,MoS₂有序堆垛结构的片层数目明显减少. 扫描电子显微镜（SEM）显示,添加适量PVP的MoS₂/石墨烯材料具有分散性更好的花瓣状微球形貌. 上述的少层有序堆垛结构及复合材料的良好分散性缩短了MoS₂中锂离子的嵌入/脱出路径,使其具有更高的容量、循环稳定性和倍率性能.     

Al含量对Pt-SO2-4 /ZrO2-Al2O3固体超强酸催化

通过向SO^2-₄ /ZrO₂催化剂中同时引入适量的Pt和Al₂O₃, 制备出了具有较高催化性能和稳定性的Pt-SO^2-₄ /ZrO₂-Al₂O₃型固体超强酸催化剂. 以正戊烷异构化反应为探针, 考察了Al含量对催化剂性能的影响; 并采用X射线衍射(XRD)、比表面积测定(BET)、红外(IR)光谱、程序升温还原(TPR)、热重-差热分析(TG-DTA)和氨-程序升温脱附(NH₃-TPD)手段对催化剂进行了表征. 结果表明, Al能够提高ZrO₂的晶化温度, 抑制硫的分解, 增加催化剂的比表面积, 增强硫氧键的结合, 提高催化剂的还原性能, 增加催化剂的酸强度和酸总量. 当Al₂O₃含量(质量分数, w)为5.0%时, Pt-SO^2-₄ /ZrO₂-Al₂O₃固体超强酸催化剂的催化活性最好, 在100 h内异戊烷收率可稳定在52.0%以上, 选择性在98.2%以上.     

合成方法对Rh/CeO2-ZrO2-La2O3催化剂的结构、表面性能及DeNOx活性的影响

用沉积沉淀法合成两种不同系列的CeO2-ZrO2-La2O3混合氧化物(ZrO2和La2O3沉积CeO2粒子(标记为A-x)以及CeO2和La2O3沉积ZrO2粒子(标记为B-x)),并用作Rh催化剂的载体。XRD、拉曼、TPR、XPS和O2脉冲等表征结果显示出不同的沉积顺序将导致不同的结构和氧化还原性能,且B-x具有更高的氧迁移性、储氧能力和表面Ce浓度。当其负载Rh后,Rh/B-x催化剂具有更高的NO和CO转化率及N2选择性,且Ce的最佳含量为50at%。这可能归因于Rh负载于富铈表面形成更多有利于NO分解的表面Ce3+活性位。     

Co取代的六铁酸盐在N2O催化分解反应中的应用

采用溶胶-凝胶法制备了Co取代的Ba₂Mg_2-xCo_xFe₁₂O₂₂(x=0.0~2.0)催化剂,并考察了其在高浓度N₂O(30vol%)分解反应中的催化活性.结果表明,Co的取代显著提高了Ba₂Mg₂Fe₁₂O₂₂催化剂活性,当x=2时,N₂O的完全分解温度从1123K降至973K;提高催化剂焙烧温度会导致其表面积降低,进而降低其催化活性;但采用微波加热则能显著提高催化剂活性.     

不同磷含量对NiMoP/Al2O3加氢处理催化剂的影响

采用NiMoP浸渍液浸渍载体γ Al₂O₃制备了不同磷含量的NiMoP/Al₂O₃加氢处理催化剂。为了研究磷对该系列催化剂活性相结构的影响,用二苯并噻吩（DBT）和喹啉为模型化合物,考察了催化剂的加氢脱硫（HDS）和加氢脱氮（HDN）性能。结果表明,添加适当的磷能够提高催化剂的HDS和HDN活性,但是高含量的磷能显著的降低催化剂的催化性能。通过对催化剂进行XRD和HRTEM表征发现,添加磷能够增加MoS2的堆积层数以及Ⅱ型“Ni-Mo-S”相的相对含量,这是因为在制备过程中添加磷降低了活性组分与载体之间的相互作用。     

超临界流体干燥法制备纳米TiO2-SnO2-SiO2复合光催化剂及其光催化性能研究

半导体多相光催化法作为一种污染治理新技术越来越受到人们的重视,在所使用的半导体光催化剂中,TiO2以无毒,催化活性高,价廉,无污染等特点,成为最具有前途的绿色环保型催化剂之一[1],但其自身具有局限性,如禁带宽度大,需在近紫外光下才能激发产生电子空穴对,对太阳光的利用率仅     

A study on methanol steam reforming to CO2 and H2 over the La2CuO4 nanofiber catalyst

The La₂CuO₄ crystal nanofibers were prepared by using single-walled carbon nanotubes as templates under mild hydrothermal conditions. The steam reforming of methanol (SRM) to CO₂ and H₂ over such nanofiber catalysts was studied. At the low temperature of 150 °C and steam/methanol=1.3, methanol was completely (100%, 13.8 g/h g catalyst) converted to hydrogen and CO₂ without the generation of CO. Within the 60 h catalyst lifespan test, methanol conversion was maintained at 98.6% (13.6 g/h g catalyst) and with 100% CO₂ selectivity. In the meantime, for distinguishing the advantage of nanoscale catalyst, the La₂CuO₄ bulk powder was prepared and tested for the SRM reaction for comparison. Compared with the La₂CuO₄ nanofiber, the bulk powder La₂CuO₄ showed worse catalytic activity for the SRM reaction. The 100% conversion of methanol was achieved at the temperature of 400 °C, with the products being H₂ and CO₂ together with CO. The catalytic activity in terms of methanol conversion dropped to 88.7% (12.2 g/h g catalyst) in 60 h. The reduction temperature for nanofiber La₂CuO₄ was much lower than that for the La₂CuO₄ bulk powder. The nanofibers were of higher specific surface area (105.0 m²/g), metal copper area and copper dispersion. The in situ FTIR and EPR experiments were employed to study the catalysts and catalytic process. In the nanofiber catalyst, there were oxygen vacancies. H₂-reduction resulted in the generation of trapped electrons [e] on the vacancy sites. Over the nanofiber catalyst, the intermediate H₂CO/HCO was stable and was reformed to CO₂ and H₂ by steam rather than being decomposed directly to CO and H₂. Over the bulk counterpart, apart from the direct decomposition of H₂CO/HCO to CO and H₂, the intermediate H₂COO might go through two decomposition ways: H₂COO=CO+H₂O and H₂COO=CO₂+H₂.     

Gas-phase phenyl acetate conversion on AlPO4, γ-Al2O3 and SiO2 catalysts

The conversion of phenyl acetate over AlPO₄ (Al/P=1), γ-Al₂O₃ and SiO₂ catalysts generated phenol, by deacetylation, ando-hydroxycetophenone, by Fries rearrangement, as the main reaction products. The activity for Fries rerrangement was in accordance with the acidity data measuredversus cyclohexene skeletal isomerization. Thus, AlPO₄ showed the highest activity. Moreover,o-hydroxy-acetophenone formation increased with the reaction temperature. Besides, in AlPO₄ catalysts 4-methylcoumarin and 2-methylchromone were also found, although in low amounts.     

Hydrogenation of citral on Ir/SiO2 catalysts. Effect of the addition of Nb2O5 on surface and catalytic properties

Hydrogenation of citral over Ir supported on SiO₂, Nb₂O₅ and Ir/Nb₂O₅-SiO₂ catalysts reduced at 473 K (LT) and 773 K (HT) was studied. High selectivity to unsaturated alcohol was found, the main reaction products being geraniol and nerol. The LT catalysts show higher conversion levels, the one with a higher Nb content displays highest conversion.