Studies on the dehydration of glycerol over niobium catalysts

The dehydration of glycerol over nanosize niobium catalysts was conducted in a stainless steel autoclave reactor. The catalysts were prepared by the calcination of niobium oxalate between 200 and 700 degrees C. Catalysts were characterized by N2 Physisorption, XRD and TPD of ammonia to investigate the effect of the calcination temperature and water on catalytic performance, catalysts' structures and acidity. Acrolein was mainly produced about 51-71% with useful by-products such as acetaldehyde and methanol. Amorphous Nb2O5 catalysts calcined at 200-400 degrees C significantly showed higher conversion of glycerol than the crystallized Nb2O5 catalyst calcined at 500-700 degrees C. Also the conversion of glycerol and selectivity of acrolein was increased with increasing the acidity of catalyst, which can be controlled by calcination temperature.     

Benzene oxidation with ozone over supported manganese oxide catalysts: effect of catalyst support and reaction conditions

Catalytic oxidation of gaseous benzene with ozone was carried out over supported manganese oxides to investigate the factors controlling the catalytic activities. The rate for benzene oxidation linearly increased with the surface area of catalyst, regardless of the kinds of catalyst support, whereas the ratio of ozone decomposition rate to benzene oxidation rate was larger for SiO(2)-supported catalyst than Al(2)O(3)-, TiO(2)-, and ZrO(2)-supported catalysts. The rate for benzene oxidation and CO(x) selectivity increased with the reaction temperature (22-100 degrees C) and were improved by the addition of water vapor to reaction gases. Benzene conversion and carbon balance increased with ozone concentration.     

Nanocrystalline ZnO thin film for photocatalytic purification of water

ZnO thin film was prepared via evaporation of Zn metal on a glass sheet following by calcination (oxidation) process. The influences of calcination parameters such as temperature and time on the surface morphology and phase structure of ZnO films were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The analysis of XRD patterns indicated that the growth of ZnO nano-structure was controlled by calcination time and temperature. Optimum ZnO nano-fibers can be formed uniformly after 2 h of oxidation at 550 °C. Nanostructured ZnO catalyst exhibited a significantly greater superiority for the photodegradation of 2,4,6-Trichlorophenol (TCP) as a model pollutant in water over photolysis via irradiation with UV of 254 nm wavelength. The role of ZnO catalyst is discussed and the chemical composition of degradation products and intermediates are identified.     

Effect of pretreatment conditions on particle size of bimetallic pt-au catalysts supported on ZnO/Al2O3 and its activity for toluene oxidation

Bimetallic Pt-Au catalysts supported on ZnO/Al2O3 were prepared by incipient wetness impregnation (IW-IMP) method with different pretreatment conditions such as flow velocity, calcination temperature, and heating rate under H2 during the calcination procedure, and characterized by X-ray diffraction (XRD), CO chemisorption, and scanning transmission electron microscopy (STEM) equipped energy dispersive spectroscopy (EDS). Furthermore, catalytic activity for complete oxidation of toluene was measured using a flow reactor under atmospheric pressure. Finally, relationship between the particle sizes with pretreatment conditions and catalytic activity for toluene on the bimetallic Pt-Au catalysts was discussed. In these results, nanosized bimetallic Pt-Au particles on ZnO/Al2O3 could be prepared by IW-IMP method. Relationship between the Pt and Au particle size and activity for toluene oxidation was clearly observed.     

Mesoporous Co3O4 for low temperature CO oxidation: effect of calcination temperatures on their catalytic performance

Mesoporous Co3O4 particles are prepared by using mesoporous silica KIT-6 (with double gyroid Ia-3d symmetry) as a hard-template and Co(No3)2 x 6H2O as an inorganic precursor. In the former section, we investigate the effect of the calcination temperatures at which the Co salts are converted into Co3O4 inside the mesopores on the textural parameters of the products. The results of N2 adsorption-desorption analysis indicates that the calcination temperatures do not obviously affect the textural parameters such as the surface areas and pore volumes. However, when the calcination temperature reaches 800 degrees C, the mesostructural ordering is dramatically decreased, resulting in the reduction of the surface areas and pore volumes. After 800 degrees C calcination, the formation of large Co3O4 grains is partially confirmed on the particle surface by SEM observation. The grain size is much larger than the mesopore size of the original KIT-6, meaning the crystal growth is continuously occurred by breaking the rigid silica frameworks. In the latter section, we discuss the effect of the calcination temperatures and textural parameters on the catalytic activity for CO oxidation by both steady state and kinetic measurements. All mesoporous Co3O4 particles show a high catalytic activity, for example, -72 degrees C for sample calcined at 450 degrees C. Only 10 degrees C difference in T50 (the temperature of 50% conversion of CO) is found between the samples with the highest and lowest catalytic activity. The values of activation energy (Ea) and pre-exponential factor (A) per unit area are almost the same between two samples calcined at 450 degrees C and 800 degrees C. It is demonstrated that calcination process can not alter the essential catalytic property of mesoporous Co3O4 particles.     

Synthesis and electrochemical performances of LiNiCuZn oxides as anode and cathode catalyst for low temperature solid oxide fuel cell

Low temperature solid oxide fuel cell (LTSOFC, 300-600 degrees C) is developed with advantages compared to conventional SOFC (800-1000 degrees C). The electrodes with good catalytic activity, high electronic and ionic conductivity are required to achieve high power output. In this work, a LiNiCuZn oxides as anode and cathode catalyst is prepared by slurry method. The structure and morphology of the prepared LiNiCuZn oxides are characterized by X-ray diffraction and field emission scanning electron microscopy. The LiNiCuZn oxides prepared by slurry method are nano Li0.28Ni0.72O, ZnO and CuO compound. The nano-crystallites are congregated to form ball-shape particles with diameter of 800-1000 nm. The LiNiCuZn oxides electrodes exhibits high ion conductivity and low polarization resistance to hydrogen oxidation reaction and oxygen reduction reaction at low temperature. The LTSOFC using the LiNiCuZn oxides electrodes demonstrates good cell performance of 1000 mW cm(-2) when it operates at 470 degrees C. It is considered that nano-composite would be an effective way to develop catalyst for LTSOFC.     

Preparation of nanosized Pt-Au alloy catalyst and its activity in methanol oxidation

The alloy catalyst has been widely used because it will be able to improve the activity and selectivity of the single metal catalyst in a given chemical reaction. In this study, the preparation and characteristics of nanosized Pt and Au particles on alumina and their catalytic activity were described. Nanosized Pt-Au catalysts were prepared by impregnation (IMP) method and deposition (DP) method using alumina or ZnO/Al2O3 as support. The size of Pt and Au particles were observed by transmission electron microscopy (TEM), energy dispersive spectroscope (EDS), and X-ray diffraction (XRD). Catalytic activity for oxidation of methanol was measured using a flow reactor. It could be seen that the Pt particle size and dispersion in the alloy catalysts was rarely influenced by preparation methods and Au particles coated by deposition method were well dispersed. TEM images showed that Au particles were well dispersed in the Pt/Au/ZnO/Al2O3 catalyst of which Au particles was supported by deposition method. The catalytic activity for methanol are given in the order of Pt-Au[IMP]/ZnO/Al2O3 > Pt[IMP]/Au[DP]/ZnO/Al2O3 > Au[DP]/Pt[IMP]/ZnO/Al2O3 > Pt-Au[DP]/ZnO/Al2O3. Therefore, Au particle size was doing not play an important role in increasing the oxidation activity, but the Au particles may promote the methanol oxidation.     

Synthesis and characterization of supported polysugar-stabilized palladium nanoparticle catalysts for enhanced hydrodechlorination of trichloroethylene

Palladium (Pd) nanoparticle catalysts were successfully synthesized within an aqueous phase using sodium carboxymethyl cellulose (CMC) as a capping ligand which offers a green alternative to conventional nanoparticle synthesis techniques. The CMC-stabilized Pd nanoparticles were subsequently dispersed within support materials using the incipient wetness impregnation technique for utilization in heterogeneous catalyst systems. The unsupported and supported (both calcined and uncalcined) Pd nanoparticle catalysts were characterized using transmission electron microscopy, energy dispersive x-ray spectrometry, x-ray diffraction, and Brunauer-Emmett-Teller surface area measurement and their catalytic activity toward the hydrodechlorination of trichloroethylene (TCE) in aqueous media was examined using homogeneous and heterogeneous catalyst systems, respectively. The unsupported Pd nanoparticles showed considerable activity toward the degradation of TCE, as demonstrated by the reaction kinetics. Although the supported Pd nanoparticle catalysts had a lower catalytic activity than the unsupported particles that were homogeneously dispersed in the aqueous solutions, the supported catalysts retained sufficient activity toward the degradation of TCE. In addition, the use of the hydrophilic Al(2)O(3) support material induced a mass transfer resistance to TCE that affected the initial hydrodechlorination rate. This paper demonstrates that supported Pd catalysts can be applied to the heterogeneous catalytic hydrodechlorination of TCE.     

Effect of nanosized gold particle addition to supported metal oxide catalyst in methanol oxidation

Gold has rarely been utilized as a catalytic component because of its poor affinity to chemical species. It is however known that nanosized gold particles promote the dissociation of oxygen or hydrogen. In this study, alumina-supported metal oxide catalysts were prepared by impregnation method and applied to methanol oxidation. The dispersion form and size of the gold particles were observed by transmission electron microscopy (TEM). In the results, the maximum catalytic activity was obtained over the ZnO/Al2O3 catalyst, and the optimum loading was 4 wt%. Furthermore, nano-sized gold particles at various loadings were added to ZnO/Al2O3 catalyst by deposition method. The gold particles on Au/ZnO/Al2O3 catalyst were well dispersed and the catalyst activity was remarkably increased compared to ZnO/Al2O3 catalyst. The role of gold particles in the increased catalytic activity is discussed and a possible mechanism is presented.     

Partial oxidation of dimethyl ether using the structured catalyst Rh/Al2O3/Al prepared through the anodic oxidation of aluminum

The partial oxidation of dimethyl ether (DME) was investigated using the structured catalyst Rh/Al2O3/Al. The porous Al2O3 layer was synthesized on the aluminum plate through anodic oxidation in an oxalic-acid solution. It was observed that about 20 nm nanopores were well developed in the Al2O3 layer. The thickness of Al2O3 layer can be adjusted by controlling the anodizing time and current density. After pore-widening and hot-water treatment, the Al2O3/Al plate was calcined at 500 degrees C for 3 h. The obtained delta-Al2O3 had a specific surface area of 160 m2/g, making it fit to be used as a catalyst support. A microchannel reactor was designed and fabricated to evaluate the catalytic activity of Rh/Al2O3/Al in the partial oxidation of DME. The structured catalyst showed an 86% maximum hydrogen yield at 450 degrees C. On the other hand, the maximum syngas yield by a pack-bed-type catalyst could be attained by using a more than fivefold Rh amount compared to that used in the structured Rh/Al2O3/Al catalyst.     

固体超强酸SO42-/TiO2-Al2O3的制备及其催化合成冰片

采用溶胶-凝胶法和浸渍法制备了系列SO_4~(2-)/TiO_2-Al_2O_3固体超强酸催化剂,运用XRD、NH_3-TPD、FT-IR、PyFTIR、XPS、SEM等技术手段,研究了复合催化剂材料的结构与性质,初步探讨了固体超强酸SO_4~(2-)/TiO_2-Al_2O_3催化剂的构效关系,得到适宜的催化剂制备条件为:n(TiO_2)/n(Al_2O_3)=1∶2、硫酸浸渍浓度1mol/L、催化剂焙烧温度500℃。考察了物料物质的量比、催化剂用量、反应时间等对催化合成冰片的影响。结果表明,在物料物质的量比为1∶0.4,催化剂用量为α-蒎烯质量的7%,采用程序升温方式(65℃-1h,75℃-4h,90℃-1h)加热的条件下,固体超强酸SO_4~(2-)/TiO_2-Al_2O_3催化剂的催化活性最高,α-蒎烯的转化率高达100%,龙脑的收率高达59.74%,SO_4~(2-)/TiO_2-Al_2O_3固体超强酸催化剂在重复使用6次的条件下,α-蒎烯的转化率均不变,龙脑的收率下降2.99%,催化剂的重复使用性良好。     

Aqueous Cr(VI) photo-reduction catalyzed by TiO2 and sulfated TiO2

TiO(2) and sulfated TiO(2) (SO(4)(2-)/TiO(2)) catalysts with different textural properties were prepared under different calcination temperatures and the photo-reduction of Cr(VI) to Cr(III) catalyzed by these catalysts was investigated. For the photocatalytic reduction of Cr(VI), the photocatalytic activities of the TiO(2) samples were found to be strongly dependent of the calcination temperature and TiO(2) calcined at 400 degrees C showed a higher catalytic activity compared to other TiO(2) catalysts. In contrast, sulfation of TiO(2) stabilized the catalytic activities of SO(4)(2-)/TiO(2) catalysts. At low calcination temperature, SO(4)(2-)/TiO(2) catalysts exhibited catalytic activities almost comparable with that of TiO(2) and the catalytic activities of SO(4)(2-)/TiO(2) catalysts were markedly higher than TiO(2) under high calcination temperature. In addition, the removal of surface SO(4)(2-) of SO(4)(2-)/TiO(2) catalyst led to a marked decrease of the catalytic activity for Cr(VI) photo-reduction, suggesting that the presence of surface SO(4)(2-) provided an acid environment over the catalyst surface and favored the photo-reduction of Cr(VI).     

Li2O–ZnO–Co3O4–TiO2 composite thin-film electrocatalyst for efficient water oxidation catalysis

Thin films of different Li₂O–ZnO–Co₃O₄–TiO₂ (LZCT) compositions were prepared and employed as electrocatalysts (i.e., anodes) to perform water oxidation reaction (WOR). The electrocatalytic activities of these thin films were compared with those exhibited by the sodium salt of cobalt phosphate (Na₂CoP₂O₇) (CP) thin-film electrocatalyst, which is a well-known water oxidation catalyst (WOC). These results suggest that the 10Li₂O–10ZnO–40Co₃O₄–40TiO₂ composition exhibits a better catalytic activity in terms of higher faradaic efficiency (>98%), lower over potentials (<400?mV), higher reaction stability (up to 30 continuous cyclic voltammetry (CV) cycles), and the rate of O₂ and H₂ gas evolution in terms of current density (about 1?mA/cm²) in comparison with those exhibited by CP thin-film electrocatalyst. Furthermore, these LZCT thin films exhibited very high specific surface area values and due to the unique microstructure of ZnCo₂O₄ phase evolved out of these LZCT compositions at a calcination temperature of 550°C for 30?min it has been found to be responsible for the higher specific surface area values measured for these thin-film compositions.     

均匀沉淀法制备ZnO、Fe/ZnO光催化剂

以六水合硝酸锌、九水合硝酸铁和CO(NH2)2为原料,采用均匀沉淀法并且改变实验条件制备了纯纳米ZnO和纳米Fe/ZnO光催化剂。通过X射线衍射(XRD)和扫描电子显微镜(SEM)对所有样品进行表征,并对部分样品进行了X射线能谱分析仪(EDS)测试。结果显示所有样品均为六方纤锌矿结构。此外,所有样品均由小颗粒聚集在一起而形成了形状、大小各不相同的团聚物或颗粒膜。而且随煅烧温度和Fe掺杂浓度的改变,Fe/ZnO样品的晶粒尺寸和表面形貌也随之变化。以甲基橙溶液作为污染物,在高压汞灯的照射下进行了光降解实验,实验结果表明:Fe掺杂Fe/ZnO样品的光催化性能相较纯纳米ZnO样品得到了改善。当Fe掺杂量为1.5%时Fe/ZnO样品的光催化性能最好;另外,适当煅烧温度也使Fe/ZnO样品的光催化活性得到了提升,其中最适煅烧温度为500℃。无论是Fe的掺杂浓度还是煅烧温度,适当的Fe的掺杂浓度和煅烧温度都有利于改善Fe/ZnO样品光催化剂的性能。     

Growth and analysis of C nanotubes on ceramic polymer-additives

C nanotubes are synthesized by catalytic route on ceramic supports (Al2O3, MgO and CaO), usually utilized for polymer reinforcing/flame-retardancy, aiming at nanotube-based hybrid preparation. Chemical vapor deposition is carried out in i-C4H10+H2 atmosphere over 17 wt% Fe-catalysts upon different conditions. In order to clarify the influence of support material, calcination (450 degrees C or 750 degrees C) and reduction temperature (500 degrees C or 600 degrees C) of the catalysts, and synthesis temperature (600 degrees C or 700 degrees C), catalysts utilized and nanotubes obtained are systematically investigated by the use of several analysis techniques (electron microscopy, X-ray diffraction, thermo-gravimetry and Raman spectroscopy). The results obtained show that, in the considered range of variation, support material is the most influential parameter. The most catalytically active alumina supports allow achieving higher yields, but involve larger metallic inclusions and lower crystalline quality. Remaining supports behave oppositely. The reasons for such differences are discussed in the light of the current assessments on the nanotube growth and the results obtained are compared with those available in literature for similar catalysts.     

Photocatalytic degradation of Direct Red 23 dye using UV/TiO2: Effect of operational parameters

In this study, the photocatalytic degradation of Direct Red 23 (Scarlet F-4BS) was investigated in UV/TiO2 system. The effect of catalyst loading and pH on the reaction rate was ascertained and optimum conditions for maximum degradation were determined. The results obtained showed that acidic pH is proper for the photocatalytic removal of Direct Red 23. In addition, the effects of several cations (Cu2+, Al3+, Cr3+, and Sn4+) and anions (BiO3(-), SO4(2-), and CN(-)) and C2H5OH were examined in this photocatalytic process. On the order hand, three types of catalysts (Fe2O3, SnO2, and ZnO) were compared with TiO2. After 90 min reaction, the relative decomposition order established was UV/TiO2>UV/SnO2>UV/Fe2O3>UV/ZnO.     

液氨沉淀法制备ZnO超微粉

以Zn(NO3 ) 2 为原料 ,NH3 ·H2 O为沉淀剂 ,采用直接沉淀法制备Zn(OH) 2 白色沉淀 ,经洗涤、干燥、煅烧后生成ZnO超微粉末。通过TEM观察到ZnO为球形晶体 ,平均粒径 15 0nm。探讨了溶液pH值、沉淀剂浓度、反应时间、反应温度对前躯体Zn(OH) 2 粒度的影响以及煅烧过程中煅烧温度与煅烧时间对ZnO粒度的影响 ,得出了最佳工艺条件。     

Synthesis and structure analysis of La0.5SR0.5TiO3 nanoparticles prepared by thermal decomposition method

La0.5Sr0.5TiO3 (LSTO) nanoparticles were synthesized by thermal decomposition method using Cl3La, CI2Sr x 6H2O and C16H28O6Ti as starting materials. The obtained precursor in a powder form was calcined at 700, 900, 1100 and 1300 degrees C for 3, 6 and 9 h in air. The structures of all samples were analyzed by XRD and some of them were taken for SEM, TEM and VSM measurements. The results from SEM showed the parallelpipe like shape of the particles with sizes distributed between 80 and 180 nm and the sizes of these particles were increased with the increasing of calcination temperature and time. The XRD's results showed the perovskite structure with the lattice type of orthorhombic at the calcination temperature of 900, 1100 and 1300 degrees C for 3, 6 and 9 h. The TiO and others unknown phase were found at low calcination temperature and they were disappeared as the calcination temperature and time were increased. The results of TEM support the orthorhombic structure of LSTO nanoparticles with crystallite size less than 200 nm as revealed by SEM and XRD. The magnetic property of all samples was measured by VSM and revealed that those prepared at 700, 900, and 1100 degrees C exhibit diamagnetic behavior, whereas one at 1300 shows ferromagnetism at room temperature. In this work, it is found that the nano-LSTO of high crystalline phase and purity can be prepared by thermal decomposition method at calcination temperature of 900 to 1300 degrees C in air for 6-9 h.     

Photocatalytic oxidation of nitric oxide with immobilized titanium dioxide films synthesized by hydrothermal method

Gas-phase photocatalytic oxidation (PCO) of nitric oxide (NO) with immobilized TiO2 films was studied in this paper. The immobilized TiO2 films were synthesized by hydrothermal method. The characterization for the physicochemical properties of catalysts prepared under different hydrothermal conditions were carried out by X-ray diffraction analysis (XRD), transmission electron microscopy (TEM), high resolution-transmission electron microscopy (HR-TEM), Brunauer-Emmett-Teller measurements (BET) and scanning electron micrograph (SEM). It was found that the PCO efficiency of the catalyst was mainly depended on the hydrothermal conditions. The optimal values of hydrothermal temperature and hydrothermal time were 200 degrees C and 24 h, respectively. Furthermore, it was also known that the photocatalytic efficiency would decrease remarkably when the calcination temperature was over than 450 degrees C. Under the optimal conditions (hydrothermal condition: 200 degrees C for 24 h; calcination temperature: 450 degrees C), the photocatalytic efficiency of catalyst could reach 60% higher than that of Degussa P25.     

Decolorization of molasses fermentation wastewater by SnO(2)-catalyzed ozonation

In the presence of O(3), the oxidative decolorization reaction on molasses fermentation wastewater with SnO(2) as a catalyst was studied. The results showed that SnO(2) accelerated the ozone oxidation reaction and the oxidative decolorization of molasses fermentation wastewater was accelerated. Influences on SnO(2) catalytic ozonation activity by precipitants and the calcination temperature were studied by XRD, IR and TG-DSC. SnO(2) prepared by ammonia as the precipitant had higher catalytic activity and a stronger dehydroxylation. The IR spectra of adsorbed pyridine showed that there were Lewis acid sites on the surface of this SnO(2) catalyst. The main factors influencing molasses fermentation wastewater oxidative decolorization were the wastewater concentration, the O(3) concentration, the pH value and the catalyst dosage. The decolorization of wastewater was improved with the increase of the wastewater dilution ratio, the ozone concentration and the catalyst dosage. High activity *OH was found to be existing with less amount and low concentration in the process of SnO(2) catalyzed ozonation decolorization.