首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
The hydrothermal transformation of calcium aluminate hydrates were investigated by in situ synchrotron X-ray powder diffraction in the temperature range 25 to 170 °C. This technique allowed the study of the detailed reaction mechanism and identification of intermediate phases. The material CaAl2O4·10H2O converted to Ca3Al2(OH)12 and amorphous aluminum hydroxide. Ca2Al2O5·8H2O transformed via the intermediate phase Ca4Al2O7·13H2O to Ca3Al2(OH)12 and gibbsite, Al(OH)3. The phase Ca4Al2O7·19H2O reacted via the same intermediate phase to Ca3Al2(OH)12 and mainly amorphous aluminum hydroxide. The powder pattern of the intermediate phase is reported.  相似文献   

2.
Layered double hydroxide pillared by Paratungstate A ion, Mg12Al6(OH)36(W7O24)·4H2O, was prepared via anion exchange reaction of the synthetic precursor, Mg4Al2(OH)12TA·xH2O (TA2−=terephthalate), and [W7O24]6− ion. Some physico-chemical properties were measured and the preparation conditions were studied. Trace aqueous organocholorine pesticide, hexachlorocyclohexane (HCH), was totally degraded and mineralized into CO2 and HCl by irradiating a Mg12Al6(OH)36(W7O24)·4H2O suspension in the near UV area. Disappearance of trace HCH follows Langmuir–Hinshelwood first-order kinetics. The model and mechanism for the photocatalytic degradation of HCH on the Mg12Al6(OH)36(W7O24)·4H2O were proposed, indicating that the interlayer space is the reaction field, and that photogeneration of OH√ radicals are responsible for the degradation pathway.  相似文献   

3.
Three compounds, K2(H2O)4H2SiMo12O40 · 7H2O (1), K2Na2(H2O)4SiW12O40 · 4H2O (2), and Na4(H2O)8SiMo12O40 · 6H2O (3) have been synthesized and structurally characterized by single-crystal X-ray analysis, IR, and thermogravimetry. Compounds 1 and 2 both show the high symmetry trigonal space group P3221 and a novel 3D network structure. The Keggin anions [SiM12O40]4−(M = Mo, W) are linked by potassium or sodium cations to generate hexagon-shaped channels along the c-axis, in which water molecules are accommodated. Compound 3 is tetragonal, space group P4/mnc constructed from [SiMo12O40]4− anions and Na ions.  相似文献   

4.
In an attempt to better understand interactions occuring at hydrated cement/organic polymer interfaces, the reaction mechanism and products formed at the interfaces between poly(acrylic acid), p(AA) or poly(acrylamide), p(AM), and Ca(OH)2 or gibbsite, Al2O3·3H2O, were explored using x-ray photoelectron spectroscopy (XPS). It was estimated that at p(AA)/Ca(OH)2 interfaces, a Ca-complexed carboxylate interfacial reaction product was formed by an ionic reaction between the COOH in p(AA) and Ca2+ ions from Ca(OH)2. A similar reaction product was formed at p(AM)/Ca(OH)2 interfaces as a result of an inter-facial transformation of amide in p(AM) into carboxylic acid, caused by the alkali-catalyzed hydrolysis of the amide. The proton-accepting hydroxyl groups existing at the outermost surface sites of Al2O2·3H2O react favorably with proton-donating COOH groups in p(AA). This acidbase interaction at the p(AA)/Al2O3·3H2O joint formed hydrogen bonds. Whereas, when the p(AM) was applied on Al2O3·3H2O surfaces, interfacial electrostatic bonds were formed through charge-transferring reaction mechanisms in which the charge density was transferred from the Al in Al2O3·3H2O to the C=0 oxygen in p(AM).  相似文献   

5.
A novel sol–gel method based on V2O5·nH2O hydro-gel was developed to synthesize nanocrystalline Li3V2(PO4)3/carbon composite material. In this route, V2O5·nH2O hydro-gel, NH4H2PO4, Li2CO3 and high-surface-area carbon were used as starting materials to prepare precursor, and the Li3V2(PO4)3/carbon was obtained by sintering precursor at 750 °C for 4 h in flowing argon. The sol–gel synthesis ensures homogeneity of the precursors and improved reactivity. The sample was characterized by XRD, SEM and TEM. X-ray diffraction results show Li3V2(PO4)3 sample is monoclinic structure with the space group of P21/n. The TEM image indicates that the Li3V2(PO4)3 particles modified by conductive carbon are about 70 nm in diameter. The Li3V2(PO4)3/carbon system showed that the discharge capacities in the first and 50th cycle are about 155.3 and 143.6 mAh/g, respectively, in the range of 3.0–4.8 V. The sol–gel method is fit for the preparation of Li3V2(PO4)3/carbon composite material which may offer some favorable properties for commercial application.  相似文献   

6.
The surface structure analysis of a model catalyst MoOx/TiO2(110) was for the first time performed by polarization-dependent total-reflection fluorescence X-ray absorption fine structure (PTRF-XAFS) in three different directions of the crystal surface. Two samples of MoOx/TiO2(110) were prepared by an impregnation of (NH4)6Mo7O24·4H2O using ultra high purity water and normal distilled water. The PTRF-XAFS analysis revealed that anisotropic Mo dimer species was preferentially formed on the TiO2(110) surface, with Mo–Mo bond (0.335 nm) parallel to the direction when the ultra high purity water was used as the solvent. On the other hand, the Mo oxide on the surface prepared using normal distilled water had a symmetric tetrahedral structure (MoO4) with Mo–O of 0.176 nm, which was due to the coexistence of alkaline metals at the surface.  相似文献   

7.
A new method through intercalation and exfoliation of VOPO4·2H2O crystallites in primary alcohol (1-propanol or 1-butanol), followed by reduction with the alcohol, have been investigated for the preparation of catalyst precursor. Lamellar compounds, consisting of V4+, P5+ and alkyl group with thin film-like morphology, were formed and was characterized by means of XRD, IR, TG/DTA, and elemental analysis. The chemical formula of the precursor obtained by exfoliation–reduction in 1-butanol was shown to be VO{(n-C4H9)0.16H0.84}PO4·0.8H2O. On the other hand, a direct reduction of VOPO4·2H2O in the alcohol gave a mixed phase shown by (VOHPO4·0.5H2O)0.3(VO{(n-C4H9)0.3H0.7}PO4·3H2O)0.7 comprising plate-like microcrystallites. These precursors transformed to (VO)2P2O7 phase during an activation process at 703 K in the presence of a mixture of n-butane 1.5% and O2 17% in He balance. The obtained (VO)2P2O7 through the exfoliation–reduction was well crystallized and consisted of thin flaky crystallites. It was found that (VO)2P2O7 thus prepared through the exfoliation–reduction was highly active and selective for oxidation of n-butane.  相似文献   

8.
A new preparation of supported MoO3 is described. Slurry MoO3/water is used instead of the solution (NH4)6Mo7O24. Preparation and HDS activity are illustrated for MoO3 supported over Al2O3, active carbon and ZrO2. Another application of the new principle is the preparation of high surface area MoO3/MgO by the reaction of MgO with slurry (NH4)6Mo7O24/methanol. Texture of MgO that is deteriorated in aqueous solution of (NH4)6Mo7O24 is stable in that slurry. “Slurry impregnation” is a special case of equilibrium adsorption impregnation. It is simple and it provides monolayer dispersion of molybdena.  相似文献   

9.
In this work, we explored the potential of mesoporous zeolite-supported Co–Mo catalyst for hydrodesulfurization of petroleum resids, atmospheric and vacuum resids at 350–450°C under 6.9 MPa of H2 pressure. A mesoporous molecular sieve of MCM-41 type was synthesized; which has SiO2/Al2O3 ratio of about 41. MCM-41 supported Co–Mo catalyst was prepared by co-impregnation of Co(NO3)2·6H2O and (NH4)6Mo7O24 followed by calcination and sulfidation. Commercial Al2O3 supported Co–Mo (criterion 344TL) and dispersed ammonium tetrathiomolybdate (ATTM) were also tested for comparison purposes. The results indicated that Co–Mo/MCM-41(H) is active for HDS, but is not as good as commercial Co–Mo/Al2O3 for desulfurization of petroleum resids. It appears that the pore size of the synthesized MCM-41 (28 Å) is not large enough to convert large-sized molecules such as asphaltene present in the petroleum resids. Removing asphaltene from the resid prior to HDS has been found to improve the catalytic activity of Co–Mo/MCM-41(H). The use of ATTM is not as effective as that of Co–Mo catalysts, but is better for conversions of >540°C fraction as compared to noncatalytic runs at 400–450°C.  相似文献   

10.
A novel microwave-assisted hydrothermal route for preparation of Co3O4 nanorods had been developed. The process contained two steps: first, nanorods of cobalt hydroxide carbonate were obtained from a mixed solution of 50 ml of 0.6 M Co(NO3)2·6H2O and 2.4 g of urea under 500 W microwave irradiated for 3 min. Then, the cobalt hydroxide carbonate nanorods were calcined at 400 °C to fabricate pure cobaltic oxide (Co3O4) nanorods. Both nanorods were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetry (TG), infrared (IR) and temperature-programmed reduction (TPR). The catalytic activity towards the degradation of phenol over Co3O4 nanorods was further studied under continuous bubbling of air through the liquid phase. The results showed that phenol was degraded into harmless products (CO2 and malonic acid). The mechanism of phenol degradation was also discussed.  相似文献   

11.
Photodegradation catalyst screening by combinatorial methodology   总被引:1,自引:0,他引:1  
In this work, a combinatorial methodology was developed for photodegradation catalyst screening. A fluorescence imaging detection system was designed for high throughput analysis, 1,6-hexamethylenediamine was used as the probe molecule for catalyst testing. The photodegradation activity of catalysts was evaluated by 1,6-hexamethylenediamine consumption during the photodegradation reaction. The methodology could provide reliable results. We found that pure TiO2, ZrO2, Nb2O5, MoO3, and WO3 did not show much activity for 1,6-hexamethylenediamine photodegradation under visible light. TiO2 catalysts doped with different metal ions were tested. When TiO2 was doped with Ta2O5, Nb2O5, V2O5, MoO3, or WO3, higher activity for photodegradation was observed. The doping of La3+, Ba2+, and Br to TiO2 did not improve the catalytic activities. When doping TiO2 with Mn2+, Cl, Al3+, Cu2+, Fe3+, Na+, Mg2+, Li+, F, Co2+, or K+, catalytic activity was lower than that of pure TiO2. After elaborate catalysts screening, we discovered new catalysts, such as 50–70% TiO2/0–20% WO3/20–40% VO2.5 and 20–30% TiO2/30–50% MoO3/40–60% VO2.5 as well as 30% WO3/20% ZrO2/50% NbO2.5 (synthesized from ZrCl4, NbCl5, and (NH4)5H5[H2(WO4)6]·H2O in ethanol solution or suspension) and 60–70% WO3/Nb2O5 (synthesized from WCl6 and NbCl5 in ethanol solution). We observed that the catalytic activity is sensitive to preparation methods and catalyst specific surface areas. When P123 (HO(CH2CH2O)20(CH2CH(CH3)O)70(CH2CH2O)20H, designated EO20PO70EO20) was used as template to synthesize mesoporous materials, the mesoporous catalysts showed higher activity than regular catalytic materials.  相似文献   

12.
The clusters Mo2O11H10, Mo3O16H14 and Mo7O32H22 of MoO3 (0 1 0) surface were studied by using ab initio HF approaches. The geometry of each cluster was fully optimized at RHF or UHF/MINI/ECP-SBK level of theory. The bonding properties, electronic structures and orbital populations of structurally different oxygens were obtained. It was shown that there exist some differences in the bonding properties between Mo atoms and the different oxygens. The symmetrically bridging oxygens exhibit more ionic feature while the terminal oxygens are more covalent. Moreover, information on explaining the active sites for the insertion of oxygen into allylic species in the second step of the oxidation processes of propylene to acrolein could be inferred from the frontier orbital populations of MoO3 surface cluster.  相似文献   

13.
A new preparation method for supported MoO3 catalyst, slurry impregnation, has been described and compared with the conventional impregnation method. Slurry MoO3/water is used instead of the solution ammonium heptamolybdate, AHM [(NH4)6Mo7O24]. The MoO3/γ-alumina, MoO3/active carbon, and MoO3/silica catalysts with different Mo loadings were prepared by slurry and by conventional method. The low solubility of MoO3 was sufficient to transport molybdenum species from solid MoO3 to the adsorbed phase. The equilibrium was achieved after several hours at 95 °C based on the loading amount of molybdenum. Only the process of drying was needed; calcination was not necessary and was left out. This is an important advantage for active carbon support because oxidative degradation of active carbon impregnated by molybdena starts at a relatively low temperature of about 250 °C during calcination on air. The activity was tested in the transesterification of dimethyl oxalate (DMO) and phenol at 180 °C. The dependences of catalytic activity on Mo loadings for the slurry prepared catalysts were similar to the dependences for the samples prepared by the conventional impregnation method with AHM. The activities of the slurry impregnation MoO3/γ-Al2O3 catalysts were almost the same as those of catalysts prepared conventionally. Although the performances of slurry impregnation MoO3/SiO2 catalysts for transesterification of DMO were slightly better than those of the corresponding catalysts prepared by conventional impregnation, no waste solution and no calcining nitrogenous gases were produced. Therefore, we conclude that the new slurry impregnation method for preparation of supported molybdenum catalysts is an environmentally friendly process and a simple, clean alternative to the conventional preparation using solutions of (NH4)6Mo7O24. The present work will lead to a remarkable improvement in the catalyst preparation for the transesterification reaction.  相似文献   

14.
Catalytic reactions of n-pentane and 1-pentene were performed as a function of reaction temperature, on different molybdenum oxides and metal surfaces. These oxides such as Mo2O5 and MoO2 were obtained following the exposure of MoO3/TiO2 to hydrogen at different temperatures up to 673 K. Metallic Mo(0) state is obtained at reduction temperatures beyond 723 K. Identification of the Mo chemical species was performed using in situ XPS-UPS surface techniques. The combination of both techniques provides valuable information on the chemical composition of the upper 10 atomic monolayers. X-ray diffraction and HRTEM techniques were also employed. The reduction procedure of MoO3 does not follow the same pathway when it is deposited on an Al2O3 support. A strong electronic interaction between the two species promotes the formation of an Al2(MoO4)3 complex as revealed by XRD measurements. Catalytic active functions present on the different Mo species surfaces are of the acidic type (Lewis and Brönsted) on Mo2O5, metal-acid (bifunctional) on MoO2 and metal function on metallic Mo(0). Consequently, a specific catalytic reaction of n-pentane, such as hydroisomerization to iso-pentane, which is rationalized in terms of a bifunctional mechanism, is expected to occur on MoO2. Different isomerization reactions of 1-pentene were obtained in the case of MoO3/TiO2 and MoO3/Al2O3 at reduction temperatures below 573 K. However, in the case of Mo on the alumina support, the conversion of 1-pentene to iso-pentane is low and irreproducible, contrary to what has been observed for Mo on titania.  相似文献   

15.
MgO-supported Mo, CoMo and NiMo sulfide hydrotreating catalysts   总被引:2,自引:0,他引:2  
The most common preparation of high surface area MgO (100–500 m2 g−1) is calcination of Mg(OH)2 obtained either by precipitation or MgO hydration or sol–gel method. Preparation of MoO3/MgO catalyst is complicated by the high reactivity of MgO to H2O and MoO3. During conventional aqueous impregnation, MgO is transformed to Mg(OH)2, and well soluble MgMoO4 is easily formed. Alternative methods, that do not impair the starting MgO so strongly, are non-aqueous slurry impregnation and thermal spreading of MoO3. Mo species of MoO3/MgO catalyst are dissolved as MgMoO4 during deposition of Co(Ni) by conventional aqueous impregnation. This can be avoided by using non-aqueous impregnation. Co(Ni)Mo/MgO catalysts must be calcined only at low temperature because Co(Ni)O and MgO easily form a solid solution. Literature data on hydrodesulfurization (HDS) activity of MgO-supported catalysts are often contradictory and do not reproduced well. However, some results suggest that very highly active HDS sites can be obtained using this support. Co(Ni)Mo/MgO catalysts prepared by non-aqueous impregnation and calcined at low temperature exhibited strong synergism in HDS activity. Co(Ni)Mo/MgO catalysts are much less deactivated by coking than their Al2O3-supported counterparts. Hydrodenitrogenation (HDN) activity of Mo/MgO catalyst is similar to the activity of Mo/Al2O3. However, the promotion effect of Co(Ni) in HDN on Co(Ni)Mo/MgO is lower than that on Co(Ni)Mo/Al2O3.  相似文献   

16.
A low-pressure steady-state technique has been used to investigate the rates and mechanisms of the oxidation of isobutane over H3[PMo12O40], CuH4[PMo12O40]2, Cu2H2[PMo12O40]2, Cu2.5H[PMo12O40]2, and Cu3[PMo12O40]2. Observed oxidation products over all catalysts are methacrolein, 3-methyl-2-oxetanone, acetic acid, carbon dioxide and water. The most selective catalyst for methacrolein formation at low temperatures (<496 °C) is Cu2.5H[PMo12O40]2, where both Cu(II) reduction and acid sites play a role. The least active catalyst at low temperatures is phosphomolybdic acid followed by Cu3[PMo12O40]2. This activity is reversed at higher temperatures. The 3-methyl-2-oxetanone is a unique product and is likely to be the precursor to methacrylic acid. Acetic acid is also probably a precursor to complete oxidation. Catalyst deactivation or restructuring is significant only over H3[PMo12O40].  相似文献   

17.
Immobilization of heavy metals by calcium sulfoaluminate cement   总被引:2,自引:0,他引:2  
Two types of calcium sulfoaluminate cement containing 20% and 30% phosphogypsum, respectively, were investigated for their ability in hazardous waste stabilization. Fourteen series of pastes were prepared, each containing the following soluble salt: Na2CrO4·4H2O; Na2Cr2O7·2H2O; CrCl3·6H2O; Pb(NO3)2; Zn(NO3)2·6H2O; ZnSO4·7H2O; and CdCl2·5H2O. The level of pollution was 0.069 mol of heavy metal per Kg of cement.

The study has been carried out by means of X-ray diffraction, thermal analysis, scanning electron microscopy, mercury intrusion porosimetry, electrical conductivity, and leaching tests. Very good retention of lead, cadmium, zinc and trivalent chromium is observed. The retention of hexavalent chromium depends upon the nature of the binder: the cement containing 20% gypsum develops the best behaviour. This is explained by the microstructure of the hydrated paste: in the paste containing 30% gypsum, delayed ettringite precipitates and damages the hardened paste.  相似文献   


18.
In situ growth of needlelike LaAl11O18 grains reinforcing Al2O3 composites can be fabricated by a coprecipitation method using La(NO3)3√6H2O and Al(NO3)3√9H2O as starting materials. The new two-step process involved firstly preparing needlelike LaAl11O18 grains distributed homogeneously in Al2O3 powder and then pressureless sintering the composite powders. The Al2O3/25 vol.%LaAl11O18 samples pressureless sintered at 1550°C for 4 h achieve relative density up to 96.5% and exhibit a bending strength of 420±30 MPa and a fracture toughness of 4.3±0.4 MPa m1/2.  相似文献   

19.
Polymerizations of propylene oxide (PO) have been carried out by using double metal cyanide (DMC) catalyst prepared by reacting ZnCl2 and K3[Co(CN)6] in the presence of tert-butyl alcohol as a complexing agents. The DMC catalyst of the molecular formula, Zn2.3Cl1.0[Co(CN)6]1.0·2.0 tBuOH·1.0H2O, is characterized by gas sorption measurements, infrared spectroscopy and X-ray powder diffraction. The structure of DMC catalyst with negligible surface area and broadened X-ray diffraction peaks is different from that of Prussian blue analogue, Zn3[Co(CN)6]2·12H2O of microporous crystalline materials. The PO polymerization behavior is tunable by combining it with various imidazolium based ionic liquids (ILs) as external additives. Thus, (1) they make the zinc-monomer bond faster activated during the initial stage of polymerization, (2) they make the zinc-monomer bond more active, (3) they stabilize the polymerization centers and prevent their decomposition, and (4) they improve important polymer properties such as molecular weight, viscosity and unsaturation level. The maximum rate of polymerization (Rp,max) of DMC catalyst increases from 2587 to 27,222 g-polymer/g-cat h by combining with 1-ethyl-3-methylimidazolium chloride (emimCl, [emimCl]/[Zn] = 1.25) at 115 °C. The induction period as the time to reach Rp,max becomes short from 321 min for DMC catalyst to 29 min for DMC/emimCl binary catalyst. The unsaturation value of polyol (0.017 mequiv./g) produced by DMC decreases to 0.005 mequiv./g by simply combining with IL. The molecular weight polyol produced by DMC catalyst increases from Mn = 3700 to more than 6000, and the viscosity of polyol decreases by combining with ILs.  相似文献   

20.
A new mixed-valent iron MOF, formulated as Fe3O(F4BDC)3(H2O)3·(DMF)3.5 (1), has been synthesized by using a perfluorinated linear dicarboxylate to link trigonal prismatic Fe33-O)(O2C–)6 clusters. The structure refinement based on single crystal X-ray diffraction data collected from 1 reveals the material exhibits the acs topology with large channels along the crystallographic c-axis. Due to the presence of fluorine atoms the organic link, 2,3,5,6-tetrafluorobenzene-1,4-dicarboxylate (F4BDC), has a 63° torsion angle between the carboxylate and aromatic planes, resulting in larger channels compared to those in the isoreticular material MOF-235. While few iron-based MOFs have demonstrated porosity, nitrogen and hydrogen sorption experiments carried out at 77 K proved the porosity of outgassed 1, which has a Langmuir surface are of 635 m2/g and a gravimetric capacity of 0.9 wt% of hydrogen at 1 bar.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号