Single-walled carbon nanotubes(SWNTs)with enriched(n,m)species are in high demand for various advanced applications.Since the SWNT structure is largely influenced by the chemistry of the active catalyst during growth ...Single-walled carbon nanotubes(SWNTs)with enriched(n,m)species are in high demand for various advanced applications.Since the SWNT structure is largely influenced by the chemistry of the active catalyst during growth process,exploiting novel catalyst with bias towards specific SWNT chiralities has been challenging.In this work,we introduce a vanadium catalyst supported by mesoporous magnesia(V-MgO)for the selective growth of SWNTs using CO chemical vapor deposition(CVD).At a reaction temperature of 650℃,the(6,5)SWNT content reaches an impressive 67.9%among all semiconducting species,exceeding the selectivity of many commercial SWNT products.Post-CVD analysis reveals that the catalyst transforms into vanadium carbide(VC),which acts as a nucleation site for SWNT growth.Molecular dynamics simulations indicate that the energy at the SWNT-VC interface and the growth kinetics of SWNTs contribute to the chirality selectivity.This research opens up possibilities for the selective synthesis of SWNTs using cost-effective early transition metals,illuminating their future applications in fields such as bioimaging.展开更多
Radio frequency plasma was used to prepare a vanadium catalyst. The resultsshowed that activating time of the catalyst could be shortened quickly and the catalytic activitywas improved to some extent with the use of p...Radio frequency plasma was used to prepare a vanadium catalyst. The resultsshowed that activating time of the catalyst could be shortened quickly and the catalytic activitywas improved to some extent with the use of plasma. Catalyst Ls-9 was prepared under an optimalcondition of 40 W discharge power, 10 min discharge time and 8 Pa gas pressure. The catalyticactivity was up to 54.7% at 410℃, which was 2.2% higher than that of the Ls-8 catalyst. Only 10 minwas needed to activate the catalyst with plasma, which was 1/9 of the traditional calcination time.For Ls-9, both the endothermic as well as the exothermic peaks detected by differential thermalanalysis shifted to higher temperatures obviously, indicating that its crystal phase could melteasily. There existed an apparent endothermic peak at 283℃. SEM photographs showed a uniform sizedistribution. It is inferred that the quadrivalent vanadium compound may exist mainly in the form ofVOSO_4.展开更多
The effect of ultrasonic cavitations on the activity of vanadium catalysts atlow temperatures for the oxidation of sulfur dioxide, in which refined carbonized mother liquor hadbeen added, was investigated. Twenty minu...The effect of ultrasonic cavitations on the activity of vanadium catalysts atlow temperatures for the oxidation of sulfur dioxide, in which refined carbonized mother liquor hadbeen added, was investigated. Twenty minutes were needed to produce obvious cavitations when thecatalyst raw material was treated in the 50 W ultrasonic generator. However, only 10 minutes wouldbe needed in a 150 W ultrasonic generator. The higher the temperature of the wet material, the lesstime was needed to produce cavitations, and the optimal temperature was 60℃. The water content inthe wet material mainly affected the quantity of cavitations. Ls-8 catalyst was prepared usingultrasonic. Its activity for conversion of SO_2 reached to 52.5% at 410℃ and 4.2% at 350℃. Thedifferential thermal analyses indicate that both endothermic peaks and exothermic peaks noticeablyshifted forward compared with Ls catalyst prepared without ultrasonic, and SEM results show auniform pore size distribution for Ls-8 catalyst.展开更多
Several novel mono（β-enaminoketonato） vanadium complexes bearing constrained [（C6Hs）C6H3C（O）=C（CH2）nCH=N-Ar]VCl2（THF）2 （V3a： n = 1, Ar = C6H5; V4a： n = 2, Ar cyclic skeleton, including C6H5; V4b： n = 2,...Several novel mono（β-enaminoketonato） vanadium complexes bearing constrained [（C6Hs）C6H3C（O）=C（CH2）nCH=N-Ar]VCl2（THF）2 （V3a： n = 1, Ar = C6H5; V4a： n = 2, Ar cyclic skeleton, including C6H5; V4b： n = 2, Ar C6F5; V4c： n = 2, Ar = （C3H7）2C6H3; V5a： n = 3, Ar = C6H5）, were synthesized and their structure and properties were characterized. The structures of V4c and V5a in solid-state were further confirmed by X-ray crystallographic analysis. Density functional theory （DFT） results indicated that these complexes showed enhanced steric hindrance around the metal center as compared with the acyclic analogues. Upon activation with Et2AlCl and in the presence of ethyl trichloroacetate as a reactivator, all of the complexes exhibited high catalytic activities （107 gPE/（molv.h）） toward ethylene polymerization, and the obtained polymers exhibited unimodal distributions （Mw/Mn = 2.0-2.3） even produced at elevated temperatures （70-100 ℃） and prolonged reaction time. When MAO was employed as a cocatalyst, they only showed moderate catalytic activities （10^5 gPE/（molv·h））, but the resulting polymers had higher molecular weights （168-241 kg/mol）. These vanadium complexes with cyclic skeleton also showed high catalytic activities toward ethylene/norbornene copolymerization. The produced copolymers displayed approximate alternating structure at high in-feed concentration of norbornene. The catalytic capabilities of these complexes could be tuned conveniently by varying ligand structure. Furthermore, the cyclic voltammetry results also proved that these complexes exhibited better redox stabilities than the complexes bearing linear skeleton.展开更多
The nanometer CeO2 powder was prepared by the method of microwave-assisted heating hydrolysis,and the nanometer CeO2-supported or ordinary CeO2-supported vanadia catalysts with different vanadium loadings(atomic ratio...The nanometer CeO2 powder was prepared by the method of microwave-assisted heating hydrolysis,and the nanometer CeO2-supported or ordinary CeO2-supported vanadia catalysts with different vanadium loadings(atomic ratios:100V/Ce=0.1,1,4,10,and 20) were prepared by an incipient-wetness impregnation method.Spectroscopic techniques(XRD,FT-IR,Raman and UV-Vis DRS) were utilized to characterize the structures of VOx/CeO2 catalysts.The results showed that the structures of CeO2-supported vanadium oxide catalysts de...展开更多
A series of imido-vanadium(Ⅴ)complexes bearing bidentate phenoxy-phosphine ligands were synthesized and characterized by NMR,elemental analysis,and single-crystal X-ray diffraction.These complexes demonstrated excell...A series of imido-vanadium(Ⅴ)complexes bearing bidentate phenoxy-phosphine ligands were synthesized and characterized by NMR,elemental analysis,and single-crystal X-ray diffraction.These complexes demonstrated excellent catalytic performance in ethylene/1-hexene copolymerization,achieving high activities of 12.0×10~6–49.0×10~6 g_(polymer)·(mol_(V))^(-1)·h^(-1)and affording random copolymers with tunable 1-hexene incorporations.These catalysts also exhibited ultrahigh activity,up to 112.2×10~6 g_(polymer)·(mol_(V))^(-1)·h^(-1),in ethylene/norbornene(NB)copolymerization,yielding cyclic olefin copolymers with adjustable NB incorporations.Remarkably,these catalysts demonstrated exceptional tolerance toward polar functional groups,enabling efficient copolymerization of ethylene with both 10-undecen-1-ol(U-OH)and 5-norbornene-2-methanol(NB-OH),incorporating about 2 mol%polar comonomers with high efficiency.Different with the catalytic behaviors in copolymerization of ethylene with nonpolar comonomers,the catalytic activities in E/U-OH copolymerization(25.7×10~6 g_(polymer)·(mol_(V))^(-1)·h^(-1))were much higher than those in E/NB-OH copolymerization(8.6×10^(6) g_(polymer)·(mol_(V))^(-1)·h^(-1)).DFT calculations revealed that the catalytic performance is governed by synergistic electronic and steric effects.For E/NB copolymerization,strong preference for cyclic olefins was attributed to favorable transition state stabilization.In polar comonomer systems,steric effects were predominant,with NB-OH exhibiting a larger buried volume around vanadium center upon coordination compared to U-OH.Overall,this work provides fundamental insights into vanadium-catalyzed(co)polymerization and offers new strategies for tailored polyolefin design.展开更多
The study of the leaching of vanadium(V) and molybdenum(Mo) from spent petrochemical catalysts in sodium hydroxide(NaO H) medium was performed using two approaches, namely, conventional leaching and microwave-assisted...The study of the leaching of vanadium(V) and molybdenum(Mo) from spent petrochemical catalysts in sodium hydroxide(NaO H) medium was performed using two approaches, namely, conventional leaching and microwave-assisted leaching methods. The influence of microwave power, leaching time, leaching temperature, and NaOH concentration on the leaching efficiency of spent petrochemical catalyst was investigated. Under microwave-assisted conditions(600 W, 10 min, 90°C, 2.0 mol·L^(-1) NaOH, and 0.20 g·mL^(-1) solid–liquid ratio), the leaching efficiencies of V and Mo reached 94.35% and 96.23%, respectively. It has been confirmed that microwave energy has considerable potential to enhance the efficiency of the leaching process and reduce the leaching time. It is suggested that the enhancement of the leaching efficiencies of V and Mo can be attributed to the existence of a thermal gradient between solid and liquid and the generation of cracks on the mineral surface.展开更多
(Imido)vanadium(V)-alkylidene complexes of type V(CHSiMe3)(NR)(OR?)(PMe3)2 [R = Ad, C6H5, 2,6-Me2C6H3, 2,6-Cl2C6H3;R?= 2,6-Me2C6H3, 2,6-i Pr2C6H3, 2,6-F2C6H3, C6F5, C6Cl5] exhibited from moderate to remarkable catalyt...(Imido)vanadium(V)-alkylidene complexes of type V(CHSiMe3)(NR)(OR?)(PMe3)2 [R = Ad, C6H5, 2,6-Me2C6H3, 2,6-Cl2C6H3;R?= 2,6-Me2C6H3, 2,6-i Pr2C6H3, 2,6-F2C6H3, C6F5, C6Cl5] exhibited from moderate to remarkable catalytic activities for ringopening metathesis polymerization(ROMP) of norbornene(NBE). The catalytic activities were affected by the ligand substituents, and V(CHSiMe3)(N-2,6-Cl2C6H3)(OC6X5)(PMe3)2(X = F, Cl) demonstrated the exceptionally high catalytic activities for ROMP of NBE.The complexes polymerized cycloheptene(CHPE) and cis-cyclooctene(COE), and ROMP of COE by the OC6 Cl5 analogue proceeded in a living manner even at 80℃, and the activity increased with increasing the temperature up to 120 ℃. Highly active catalysts for ROMP of cyclic olefins(NBE, cyclopentene, and CHPE) can be generated in situ by premixing isolated V(CHSiMe3)(NC6F5)(O-2,6-iPr2C6H3)(PMe3)2 with 1.0 equiv. of C6F5OH or C6Cl5OH via immediate phenoxy exchange;the activity was affected by the kind of phenol added [TOF in the ROMPs of NBE: 4.62 × 10^4 min^–1(upon addition of C6F5OH) versus 37.3 min^–1(none)].展开更多
Experiments were carried out by adding CaF2 and NaF as catalysts in an Ar atmosphere to study the isothermal reduction kinetics of vanadium titano-magnetite carbon composite pellets under high temperature in the range...Experiments were carried out by adding CaF2 and NaF as catalysts in an Ar atmosphere to study the isothermal reduction kinetics of vanadium titano-magnetite carbon composite pellets under high temperature in the range from 1 473 to 1 673 K. The scanning electron microscope （SEM） was used to characterize the microstructure of product. By analyzing reduction mechanism, it was found that the rate controlling step was gas diffusion, and the activation energy was 178.39 kJ/mol without adding any catalysts. Adding CaF2 or NaF of 3% to vanadium titano-magnetite carbon composite pellets can decrease the apparent activation energy of reduction, and the decrease extent was 14.95 and 15.79 kJ/mol, respectively. In addition, temperature was an important factor influencing on reaction rate.展开更多
Vanadium-titanium-based catalysts are the most widely used industrial materials for NO_x removal from coal-fired power plants. Owing to their relatively poor low-temperature deNO_x activity, low thermal stability, ins...Vanadium-titanium-based catalysts are the most widely used industrial materials for NO_x removal from coal-fired power plants. Owing to their relatively poor low-temperature deNO_x activity, low thermal stability, insufficient Hg^0 oxidation activity, SO_2 oxidation, ammonia slip, and other disadvantages,modifications to traditional vanadium-titanium-based selective catalytic reduction（SCR）catalysts have been attempted by many researchers to promote their relevant performance. This article reviewed the research progress of modified vanadium-titanium-based SCR catalysts from seven aspects, namely,（1） improving low-temperature deNO_x efficiency,（2） enhancing thermal stability,（3） improving Hg^0 oxidation efficiency,（4） oxidizing slip ammonia,（5） reducing SO_2 oxidation,（6） increasing alkali resistance, and（7） others. Their catalytic performance and the influence mechanisms have been discussed in detail. These catalysts were also divided into different categories according to their modified components such as noble metals（e.g., silver, ruthenium）, transition metals（e.g., manganese, iron, copper, zirconium, etc.）, rare earth metals（e.g., cerium, praseodymium）,and other metal chlorides（e.g., calcium chloride, copper chloride） and non-metals（fluorine,sulfur, silicon, nitrogen, etc.）. The advantages and disadvantages of these catalysts were summarized.Based on previous studies and the author＇s point of view, doping the appropriate modified components is beneficial to further improve the overall performance of vanadium-titanium-based SCR catalysts. This has enormous development potential and is a promising way to realize the control of multiple pollutants on the basis of the existing flue gas treatment system.展开更多
The selective oxidation of n-butane to maleic anhydride (MA) on a vanadium-phosphorus oxide (VPO) catalyst was studied using on-line gas-chromatography combined with mass spectrometry(GC-MS) and transient response tec...The selective oxidation of n-butane to maleic anhydride (MA) on a vanadium-phosphorus oxide (VPO) catalyst was studied using on-line gas-chromatography combined with mass spectrometry(GC-MS) and transient response technique. The reaction intermediates, buterie and furan, were found in the reaction effluent under near industrial feed condition (3% butane+15%O2), while dihydrofuran was detected at high butane concentration (12% butane, 5%O2). Some intermediates of MA decomposition were also identified. Detection of these intermediates shows that the vanadium phosphorus oxides are able to dehydrogenate butane to butene, and butene further to form MA. Based on these observations, a modified scheme of reaction network is proposed. The transient experiments show that butane in the gas phase may directly react with oxygen both on the surface and from the metal oxide lattice, without a proceeding adsorption step. Gas phase oxygen can be adsorbed and transformed to surface lattice oxygen but it can not participate in selective oxidation. Adsorbed oxygen leads to deep oxidation, while lattice oxygen leads to selective oxidation.展开更多
The addition of distillation residues to the FCC feedstock leads to increased vanadiumloading on catalyst and the problems in catalyst deactivation.The deactivation process is related tothe destructive attack on the z...The addition of distillation residues to the FCC feedstock leads to increased vanadiumloading on catalyst and the problems in catalyst deactivation.The deactivation process is related tothe destructive attack on the zeolite crystallite by V<sub>2</sub>O<sub>5</sub>.Formation of low melting pointV<sub>2</sub>O<sub>5</sub>-USY-Na<sub>2</sub>O phases accelerates the diffusion of vanadium through the catalyst.A proposedmechanism,based on accelerated dealumination,is shown in the paper.Comparative vanadiumtrapping performances have been tested for FCC catalysts and the crystalline ABO<sub>3</sub> as an effectivevanadium trap is demonstrated in laboratory tests.展开更多
Large quantities of spent hydrodesulfurization (HDS) catalysts are available from petrochemical industry. Disposal of spent catalyst is a problem as it falls under the category of hazardous industrial waste due to its...Large quantities of spent hydrodesulfurization (HDS) catalysts are available from petrochemical industry. Disposal of spent catalyst is a problem as it falls under the category of hazardous industrial waste due to its vanadium concentration. Most of these catalysts are usually supported on alumina containing a variable percentage of elements such as nickel or molybdenum. Hence these catalysts contain environmentally critical, and economically valuable metals such as molyb denum, vanadium, and, nickel. In this paper, a spent HDS catalyst was treated with caustic soda solution. Parameters such as temperature, time, and NaOH solution concentration have been studied thoroughly, in order to settle the appropriate conditions for the maximum recovery of molybdenum and vanadium. Under the best leaching conditions (20 %w NaOH, room temperature, 2 h) about 95% recovery of Mo and V was achieved, and the recovery of nickel obtained was of 99% in the form of NiAlO4.展开更多
Magnesium chloride supported vanadium/titanium bimetallic Ziegler-Natta catalysts with di-i-butyl phthalate as internal donor for copolymerization of ethylene and propylene were prepared. The effects of reaction tempe...Magnesium chloride supported vanadium/titanium bimetallic Ziegler-Natta catalysts with di-i-butyl phthalate as internal donor for copolymerization of ethylene and propylene were prepared. The effects of reaction temperature, ethylene/propylene molar ratio, aluminium/vanadium （Al/V） molar ratio and titanium/vanadium molar ratio on the catalytic activity were investigated. The molecular weight, molecular weight distribution, sequence composition and crystallinity of the products were measured by gel permeation chromatography, ^13C-NMR and differential scanning calorimetry analysis, respectively. In comparison to the vanadium and titanium catalysts, the bimetallic catalyst showed higher catalytic activity and better copolymerization performance. The obtained ethylene/propylene copolymers have high molecular weight （105）, broad molecular weight distribution, high propylene content with random or short blocked sequence structures （rErp = 1.919）, low melting temperatures and low crystallinities （Xc 〈 20%）.展开更多
Phase composition and surface characterization of vanadium-phosphorus catalysts containing rare earth elements were investigated by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), NH3-tempera...Phase composition and surface characterization of vanadium-phosphorus catalysts containing rare earth elements were investigated by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), NH3-temperature programmed desorption (NH3-TPD) and so on. The catalysts were used for the selective oxidation of n-butane to maleic anhydride. Catalytic performance has been carried out in a fixed-bed reactor. Experimental results showed that yield of maleic anhydride was enhanced by 4%～15% over vanadium-phosphorus catalysts by the addition of rare earth elements. Rare earth elements as promotors played the role of increasing surface acidity of the catalysts.展开更多
A novel vanadium oxide catalyst supported on active carbon was prepared by an incipient wetness impregnation method, and the precursor was obtained from oxalic acid aqueous solutions of NH4VO3. The catalyst was applie...A novel vanadium oxide catalyst supported on active carbon was prepared by an incipient wetness impregnation method, and the precursor was obtained from oxalic acid aqueous solutions of NH4VO3. The catalyst was applied liquid phase oxidation of glyoxal to glyoxylic acid. It was found that V2O5/C catalyst exhibited obvious activity for glyoxal oxidation. Glyoxylic acid could be obtained without pH regulation during the reaction. By using this catalyst, the conversion of glyoxal and the yield of glyoxalic acid were 29.2% and 13.6%, respectively at 313 K and oxygen flow 0.1 L/rain after reaction for 10 h.展开更多
Vanadium（III） complexes bearing thiophenol-phosphine ligands （2a-2b） （2-R-6-PPh2-C6H2S） VC12（THF）2 （2a： R = H; 2b： R = MeaSi） were prepared from VCla（THF）3 by treating with 1.0 equiv of the ligand in tet...Vanadium（III） complexes bearing thiophenol-phosphine ligands （2a-2b） （2-R-6-PPh2-C6H2S） VC12（THF）2 （2a： R = H; 2b： R = MeaSi） were prepared from VCla（THF）3 by treating with 1.0 equiv of the ligand in tetrahydrofuran in the presence of excess triethylamine. The two complexes were characterized by FTIR and mass spectra as well as elemental analyses. On activation with Et2AIC1, these complexes exhibited high catalytic activities （up to 22.1 kg PE/（mmolv.h.bar）） even at high temperature （70 ℃）, and produced high molecular weight polymers with unimodal molecular weight distributions, indicating the polymerization took place in a single-site nature. This result may be attributed to benefits of introduction of second-row donor atoms for adjusting charge density of the vanadium centers. In addition, these complexes also exhibited high catalytic activities for ethylene/1-hexene copolymerization. Catalytic activity, comonomer incorporation and polymer molecular weight can be controlled in a wide range by the variation of catalyst structure and the reaction parameters such as A1/V molar ratio, comonomer feed concentration and polymerization reaction temperature.展开更多
Precursor decomposition was used for the preparation of VTeO/SBA-15 catalyst for the selective oxidation of propane to acrolein. The catalyst shows a better performance compared with those prepared by conventional imp...Precursor decomposition was used for the preparation of VTeO/SBA-15 catalyst for the selective oxidation of propane to acrolein. The catalyst shows a better performance compared with those prepared by conventional impregnant method. A yield of 9.3% of acrolein was achieved with 2% V loadings at 500 ℃. XRD, N2-adsorption, H2-TPR, Py-IR and XPS measurements were used to unclose the relationship between the structure and performance of the catalyst.展开更多
Mono salicylaldiminato vanadium（Ⅲ） complexes （1a-1f） [RN = CH（ArO）]VC12（THF）2 （Ar = C6H4 （1a-1e）, R = Ph, 1a; R = p-CFaPh, 1b; R = 2,6-Me2Ph, 1c; R = 2,6-iPrEPh, 1d; R = eyclohexyl, 1e; Ar = C6HEtBU2（2,4...Mono salicylaldiminato vanadium（Ⅲ） complexes （1a-1f） [RN = CH（ArO）]VC12（THF）2 （Ar = C6H4 （1a-1e）, R = Ph, 1a; R = p-CFaPh, 1b; R = 2,6-Me2Ph, 1c; R = 2,6-iPrEPh, 1d; R = eyclohexyl, 1e; Ar = C6HEtBU2（2,4）, R = 2,6-iPrEPh, 1f） and bis（salicylaldiminato） vanadium（III） complexes （2a-2f） [RN ： CH（ArO）]EVCI（THF）x （Ar = C6H4 （2a-2e）, x = 1 （2a-2e）, R = Ph, 2a; R = p-CF3Ph, 2b; R = 2,6-Me2Ph, 2c; R = 2,6-iPr2Ph, 2d; R = cyclohexyl, 2e; Ar = C6HEtBU2（2,4）, R = 2,6-iPrEPh, x = 0, 2f） have been evaluated as the active catalysts for ethylene/1-hexene copolymerization in the presence of Et2A1C1. The ligand substitution pattern and the catalyst structure model significantly influenced the polymerization behaviors such as the catalytic activity, the molecular weight and molecular weight distribution of the copolymers etc. The highest catalytic activity of 8.82 kg PE/（mmolv.h） was observed for vanadium catalyst 2d with two 2,6-diisopropylphenyl substituted salicylaldiminato ligands. The copolymer with the highest molecular weight was obtained by using mono salieylaldiminato vanadium catalyst 1 f having ligands with tert-butyl at the ortho and para of the aryloxy moiety.展开更多
Extraction of vanadium from black shale was attempted in pressure acid leaching.The chemical components of the sample obtained from Guizhou Province of China show that it contains 3.258%V2O5,52.880%SiO2 and 16.140%Al2...Extraction of vanadium from black shale was attempted in pressure acid leaching.The chemical components of the sample obtained from Guizhou Province of China show that it contains 3.258%V2O5,52.880%SiO2 and 16.140%Al2O3.Phase analyses of vanadium indicates vanadium mainly exists in the free oxide and mica.Vanadium contents in the two phases are 18%and 53%, respectively.The contents of V3 +,V 4+and V 5+are almost equal.Under the optimum parameters of one-step leaching(reaction time of 3 h,sulfuric addition of 25%,temperature of 150℃,liquid to solid ratio of 1.2 mL/g,catalyst(FeSO4)addition of 5%and size of 85%particle 0.074 mm),about 77%of vanadium is recovered.After two-step countercurrent leaching,the leach recovery of vanadium can reach above 90%.Air replacing oxygen is completely feasible.The impurity metals can dissolve into solution in different degrees.展开更多
基金financially supported by the Key Basic Research Project of Shandong Province(No.ZR2019ZD49)Taishan Scholar Foundation of Shandong Province(No.tstp20230627)Open Research Fund of State Key Laboratory of Polymer Physics and Chemistry,Changchun Institute of Applied Chemistry,Chinese Academy of Sciences。
文摘Single-walled carbon nanotubes(SWNTs)with enriched(n,m)species are in high demand for various advanced applications.Since the SWNT structure is largely influenced by the chemistry of the active catalyst during growth process,exploiting novel catalyst with bias towards specific SWNT chiralities has been challenging.In this work,we introduce a vanadium catalyst supported by mesoporous magnesia(V-MgO)for the selective growth of SWNTs using CO chemical vapor deposition(CVD).At a reaction temperature of 650℃,the(6,5)SWNT content reaches an impressive 67.9%among all semiconducting species,exceeding the selectivity of many commercial SWNT products.Post-CVD analysis reveals that the catalyst transforms into vanadium carbide(VC),which acts as a nucleation site for SWNT growth.Molecular dynamics simulations indicate that the energy at the SWNT-VC interface and the growth kinetics of SWNTs contribute to the chirality selectivity.This research opens up possibilities for the selective synthesis of SWNTs using cost-effective early transition metals,illuminating their future applications in fields such as bioimaging.
基金The project is supported by the National Natural Science Foundation of China (No.20176065)
文摘Radio frequency plasma was used to prepare a vanadium catalyst. The resultsshowed that activating time of the catalyst could be shortened quickly and the catalytic activitywas improved to some extent with the use of plasma. Catalyst Ls-9 was prepared under an optimalcondition of 40 W discharge power, 10 min discharge time and 8 Pa gas pressure. The catalyticactivity was up to 54.7% at 410℃, which was 2.2% higher than that of the Ls-8 catalyst. Only 10 minwas needed to activate the catalyst with plasma, which was 1/9 of the traditional calcination time.For Ls-9, both the endothermic as well as the exothermic peaks detected by differential thermalanalysis shifted to higher temperatures obviously, indicating that its crystal phase could melteasily. There existed an apparent endothermic peak at 283℃. SEM photographs showed a uniform sizedistribution. It is inferred that the quadrivalent vanadium compound may exist mainly in the form ofVOSO_4.
基金Project(20176065)supported by the National Natural Science Foundation of China.
文摘The effect of ultrasonic cavitations on the activity of vanadium catalysts atlow temperatures for the oxidation of sulfur dioxide, in which refined carbonized mother liquor hadbeen added, was investigated. Twenty minutes were needed to produce obvious cavitations when thecatalyst raw material was treated in the 50 W ultrasonic generator. However, only 10 minutes wouldbe needed in a 150 W ultrasonic generator. The higher the temperature of the wet material, the lesstime was needed to produce cavitations, and the optimal temperature was 60℃. The water content inthe wet material mainly affected the quantity of cavitations. Ls-8 catalyst was prepared usingultrasonic. Its activity for conversion of SO_2 reached to 52.5% at 410℃ and 4.2% at 350℃. Thedifferential thermal analyses indicate that both endothermic peaks and exothermic peaks noticeablyshifted forward compared with Ls catalyst prepared without ultrasonic, and SEM results show auniform pore size distribution for Ls-8 catalyst.
基金the National Natural Science Foundation of China(No.21234006)China National High-tech R&D Program(No.2015AA034002)
文摘Several novel mono（β-enaminoketonato） vanadium complexes bearing constrained [（C6Hs）C6H3C（O）=C（CH2）nCH=N-Ar]VCl2（THF）2 （V3a： n = 1, Ar = C6H5; V4a： n = 2, Ar cyclic skeleton, including C6H5; V4b： n = 2, Ar C6F5; V4c： n = 2, Ar = （C3H7）2C6H3; V5a： n = 3, Ar = C6H5）, were synthesized and their structure and properties were characterized. The structures of V4c and V5a in solid-state were further confirmed by X-ray crystallographic analysis. Density functional theory （DFT） results indicated that these complexes showed enhanced steric hindrance around the metal center as compared with the acyclic analogues. Upon activation with Et2AlCl and in the presence of ethyl trichloroacetate as a reactivator, all of the complexes exhibited high catalytic activities （107 gPE/（molv.h）） toward ethylene polymerization, and the obtained polymers exhibited unimodal distributions （Mw/Mn = 2.0-2.3） even produced at elevated temperatures （70-100 ℃） and prolonged reaction time. When MAO was employed as a cocatalyst, they only showed moderate catalytic activities （10^5 gPE/（molv·h））, but the resulting polymers had higher molecular weights （168-241 kg/mol）. These vanadium complexes with cyclic skeleton also showed high catalytic activities toward ethylene/norbornene copolymerization. The produced copolymers displayed approximate alternating structure at high in-feed concentration of norbornene. The catalytic capabilities of these complexes could be tuned conveniently by varying ligand structure. Furthermore, the cyclic voltammetry results also proved that these complexes exhibited better redox stabilities than the complexes bearing linear skeleton.
基金supported by the National Natural Science Foundation of China (20803093,20833011,20525621)the Doctor Select Foundation for the University of State Education Ministry (200804251016)+1 种基金the Beijing Outstanding Ph.D.Thesis Foundation (YB 20091141401)the Hi-Tech Research and Development Program (863) of China (SQ2009AA06Z3488052)
文摘The nanometer CeO2 powder was prepared by the method of microwave-assisted heating hydrolysis,and the nanometer CeO2-supported or ordinary CeO2-supported vanadia catalysts with different vanadium loadings(atomic ratios:100V/Ce=0.1,1,4,10,and 20) were prepared by an incipient-wetness impregnation method.Spectroscopic techniques(XRD,FT-IR,Raman and UV-Vis DRS) were utilized to characterize the structures of VOx/CeO2 catalysts.The results showed that the structures of CeO2-supported vanadium oxide catalysts de...
基金financially supported by the National Natural Science Foundation of China(No.52130307)。
文摘A series of imido-vanadium(Ⅴ)complexes bearing bidentate phenoxy-phosphine ligands were synthesized and characterized by NMR,elemental analysis,and single-crystal X-ray diffraction.These complexes demonstrated excellent catalytic performance in ethylene/1-hexene copolymerization,achieving high activities of 12.0×10~6–49.0×10~6 g_(polymer)·(mol_(V))^(-1)·h^(-1)and affording random copolymers with tunable 1-hexene incorporations.These catalysts also exhibited ultrahigh activity,up to 112.2×10~6 g_(polymer)·(mol_(V))^(-1)·h^(-1),in ethylene/norbornene(NB)copolymerization,yielding cyclic olefin copolymers with adjustable NB incorporations.Remarkably,these catalysts demonstrated exceptional tolerance toward polar functional groups,enabling efficient copolymerization of ethylene with both 10-undecen-1-ol(U-OH)and 5-norbornene-2-methanol(NB-OH),incorporating about 2 mol%polar comonomers with high efficiency.Different with the catalytic behaviors in copolymerization of ethylene with nonpolar comonomers,the catalytic activities in E/U-OH copolymerization(25.7×10~6 g_(polymer)·(mol_(V))^(-1)·h^(-1))were much higher than those in E/NB-OH copolymerization(8.6×10^(6) g_(polymer)·(mol_(V))^(-1)·h^(-1)).DFT calculations revealed that the catalytic performance is governed by synergistic electronic and steric effects.For E/NB copolymerization,strong preference for cyclic olefins was attributed to favorable transition state stabilization.In polar comonomer systems,steric effects were predominant,with NB-OH exhibiting a larger buried volume around vanadium center upon coordination compared to U-OH.Overall,this work provides fundamental insights into vanadium-catalyzed(co)polymerization and offers new strategies for tailored polyolefin design.
基金financially supported by the High-degree Talent Introduction Program of Guangdong Academy of Sciences(No.2017GDASCX-0841)the Science and Technology Program of Guangzhou(No.201607020021)+2 种基金the National Natural Science Foundation of China(No.51304055)the Innovative Platform Construction Program of Guangdong Academy of Sciences(No.2017GDASCX-0109)the Pearl River Nova Program of Guangzhou(No.201806010016)
文摘The study of the leaching of vanadium(V) and molybdenum(Mo) from spent petrochemical catalysts in sodium hydroxide(NaO H) medium was performed using two approaches, namely, conventional leaching and microwave-assisted leaching methods. The influence of microwave power, leaching time, leaching temperature, and NaOH concentration on the leaching efficiency of spent petrochemical catalyst was investigated. Under microwave-assisted conditions(600 W, 10 min, 90°C, 2.0 mol·L^(-1) NaOH, and 0.20 g·mL^(-1) solid–liquid ratio), the leaching efficiencies of V and Mo reached 94.35% and 96.23%, respectively. It has been confirmed that microwave energy has considerable potential to enhance the efficiency of the leaching process and reduce the leaching time. It is suggested that the enhancement of the leaching efficiencies of V and Mo can be attributed to the existence of a thermal gradient between solid and liquid and the generation of cracks on the mineral surface.
基金partly supported by Grant-in-Aid for Scientific Research on Innovative Areas ("3D Active-Site Science", No. 26105003) from The Ministry of Education, Culture, Sports, Science and Technology (MEXT), JapanGrant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science (JSPS, Nos. 15H03812, 18H01982)the Tokyo Metropolitan government (Tokyo Human Resources Fund for City Diplomacy) for pre-doctoral fellowship
文摘(Imido)vanadium(V)-alkylidene complexes of type V(CHSiMe3)(NR)(OR?)(PMe3)2 [R = Ad, C6H5, 2,6-Me2C6H3, 2,6-Cl2C6H3;R?= 2,6-Me2C6H3, 2,6-i Pr2C6H3, 2,6-F2C6H3, C6F5, C6Cl5] exhibited from moderate to remarkable catalytic activities for ringopening metathesis polymerization(ROMP) of norbornene(NBE). The catalytic activities were affected by the ligand substituents, and V(CHSiMe3)(N-2,6-Cl2C6H3)(OC6X5)(PMe3)2(X = F, Cl) demonstrated the exceptionally high catalytic activities for ROMP of NBE.The complexes polymerized cycloheptene(CHPE) and cis-cyclooctene(COE), and ROMP of COE by the OC6 Cl5 analogue proceeded in a living manner even at 80℃, and the activity increased with increasing the temperature up to 120 ℃. Highly active catalysts for ROMP of cyclic olefins(NBE, cyclopentene, and CHPE) can be generated in situ by premixing isolated V(CHSiMe3)(NC6F5)(O-2,6-iPr2C6H3)(PMe3)2 with 1.0 equiv. of C6F5OH or C6Cl5OH via immediate phenoxy exchange;the activity was affected by the kind of phenol added [TOF in the ROMPs of NBE: 4.62 × 10^4 min^–1(upon addition of C6F5OH) versus 37.3 min^–1(none)].
基金Item Sponsored by National Key Technology Research and Development Program of China(2008BAB32B05)
文摘Experiments were carried out by adding CaF2 and NaF as catalysts in an Ar atmosphere to study the isothermal reduction kinetics of vanadium titano-magnetite carbon composite pellets under high temperature in the range from 1 473 to 1 673 K. The scanning electron microscope （SEM） was used to characterize the microstructure of product. By analyzing reduction mechanism, it was found that the rate controlling step was gas diffusion, and the activation energy was 178.39 kJ/mol without adding any catalysts. Adding CaF2 or NaF of 3% to vanadium titano-magnetite carbon composite pellets can decrease the apparent activation energy of reduction, and the decrease extent was 14.95 and 15.79 kJ/mol, respectively. In addition, temperature was an important factor influencing on reaction rate.
基金supported by the Science and Technology Plan Project of Hebei Province of China(16273703D)the Fundamental Research Funds for the Central Universities(2015ZD24,2017XS123)~~
文摘Vanadium-titanium-based catalysts are the most widely used industrial materials for NO_x removal from coal-fired power plants. Owing to their relatively poor low-temperature deNO_x activity, low thermal stability, insufficient Hg^0 oxidation activity, SO_2 oxidation, ammonia slip, and other disadvantages,modifications to traditional vanadium-titanium-based selective catalytic reduction（SCR）catalysts have been attempted by many researchers to promote their relevant performance. This article reviewed the research progress of modified vanadium-titanium-based SCR catalysts from seven aspects, namely,（1） improving low-temperature deNO_x efficiency,（2） enhancing thermal stability,（3） improving Hg^0 oxidation efficiency,（4） oxidizing slip ammonia,（5） reducing SO_2 oxidation,（6） increasing alkali resistance, and（7） others. Their catalytic performance and the influence mechanisms have been discussed in detail. These catalysts were also divided into different categories according to their modified components such as noble metals（e.g., silver, ruthenium）, transition metals（e.g., manganese, iron, copper, zirconium, etc.）, rare earth metals（e.g., cerium, praseodymium）,and other metal chlorides（e.g., calcium chloride, copper chloride） and non-metals（fluorine,sulfur, silicon, nitrogen, etc.）. The advantages and disadvantages of these catalysts were summarized.Based on previous studies and the author＇s point of view, doping the appropriate modified components is beneficial to further improve the overall performance of vanadium-titanium-based SCR catalysts. This has enormous development potential and is a promising way to realize the control of multiple pollutants on the basis of the existing flue gas treatment system.
基金Supported by the National Natural Science Foundation of China (No. 29792073-3).
文摘The selective oxidation of n-butane to maleic anhydride (MA) on a vanadium-phosphorus oxide (VPO) catalyst was studied using on-line gas-chromatography combined with mass spectrometry(GC-MS) and transient response technique. The reaction intermediates, buterie and furan, were found in the reaction effluent under near industrial feed condition (3% butane+15%O2), while dihydrofuran was detected at high butane concentration (12% butane, 5%O2). Some intermediates of MA decomposition were also identified. Detection of these intermediates shows that the vanadium phosphorus oxides are able to dehydrogenate butane to butene, and butene further to form MA. Based on these observations, a modified scheme of reaction network is proposed. The transient experiments show that butane in the gas phase may directly react with oxygen both on the surface and from the metal oxide lattice, without a proceeding adsorption step. Gas phase oxygen can be adsorbed and transformed to surface lattice oxygen but it can not participate in selective oxidation. Adsorbed oxygen leads to deep oxidation, while lattice oxygen leads to selective oxidation.
文摘The addition of distillation residues to the FCC feedstock leads to increased vanadiumloading on catalyst and the problems in catalyst deactivation.The deactivation process is related tothe destructive attack on the zeolite crystallite by V<sub>2</sub>O<sub>5</sub>.Formation of low melting pointV<sub>2</sub>O<sub>5</sub>-USY-Na<sub>2</sub>O phases accelerates the diffusion of vanadium through the catalyst.A proposedmechanism,based on accelerated dealumination,is shown in the paper.Comparative vanadiumtrapping performances have been tested for FCC catalysts and the crystalline ABO<sub>3</sub> as an effectivevanadium trap is demonstrated in laboratory tests.
文摘Large quantities of spent hydrodesulfurization (HDS) catalysts are available from petrochemical industry. Disposal of spent catalyst is a problem as it falls under the category of hazardous industrial waste due to its vanadium concentration. Most of these catalysts are usually supported on alumina containing a variable percentage of elements such as nickel or molybdenum. Hence these catalysts contain environmentally critical, and economically valuable metals such as molyb denum, vanadium, and, nickel. In this paper, a spent HDS catalyst was treated with caustic soda solution. Parameters such as temperature, time, and NaOH solution concentration have been studied thoroughly, in order to settle the appropriate conditions for the maximum recovery of molybdenum and vanadium. Under the best leaching conditions (20 %w NaOH, room temperature, 2 h) about 95% recovery of Mo and V was achieved, and the recovery of nickel obtained was of 99% in the form of NiAlO4.
基金supported by the Program for New Century Excellent Talents in Universities(NCET-07-0142)the Program for New Century Excellent Talents in Heilongjiang Provincial Universities(NCET-06-010)+1 种基金the National Natural Science Foundation of China(No.20972025)the Science Foundation of Tianjin University of Science & Technology(No.20090420)
文摘Magnesium chloride supported vanadium/titanium bimetallic Ziegler-Natta catalysts with di-i-butyl phthalate as internal donor for copolymerization of ethylene and propylene were prepared. The effects of reaction temperature, ethylene/propylene molar ratio, aluminium/vanadium （Al/V） molar ratio and titanium/vanadium molar ratio on the catalytic activity were investigated. The molecular weight, molecular weight distribution, sequence composition and crystallinity of the products were measured by gel permeation chromatography, ^13C-NMR and differential scanning calorimetry analysis, respectively. In comparison to the vanadium and titanium catalysts, the bimetallic catalyst showed higher catalytic activity and better copolymerization performance. The obtained ethylene/propylene copolymers have high molecular weight （105）, broad molecular weight distribution, high propylene content with random or short blocked sequence structures （rErp = 1.919）, low melting temperatures and low crystallinities （Xc 〈 20%）.
文摘Phase composition and surface characterization of vanadium-phosphorus catalysts containing rare earth elements were investigated by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), NH3-temperature programmed desorption (NH3-TPD) and so on. The catalysts were used for the selective oxidation of n-butane to maleic anhydride. Catalytic performance has been carried out in a fixed-bed reactor. Experimental results showed that yield of maleic anhydride was enhanced by 4%～15% over vanadium-phosphorus catalysts by the addition of rare earth elements. Rare earth elements as promotors played the role of increasing surface acidity of the catalysts.
文摘A novel vanadium oxide catalyst supported on active carbon was prepared by an incipient wetness impregnation method, and the precursor was obtained from oxalic acid aqueous solutions of NH4VO3. The catalyst was applied liquid phase oxidation of glyoxal to glyoxylic acid. It was found that V2O5/C catalyst exhibited obvious activity for glyoxal oxidation. Glyoxylic acid could be obtained without pH regulation during the reaction. By using this catalyst, the conversion of glyoxal and the yield of glyoxalic acid were 29.2% and 13.6%, respectively at 313 K and oxygen flow 0.1 L/rain after reaction for 10 h.
基金supported by the National Natural Science Foundation of China (No. 21234006)
文摘Vanadium（III） complexes bearing thiophenol-phosphine ligands （2a-2b） （2-R-6-PPh2-C6H2S） VC12（THF）2 （2a： R = H; 2b： R = MeaSi） were prepared from VCla（THF）3 by treating with 1.0 equiv of the ligand in tetrahydrofuran in the presence of excess triethylamine. The two complexes were characterized by FTIR and mass spectra as well as elemental analyses. On activation with Et2AIC1, these complexes exhibited high catalytic activities （up to 22.1 kg PE/（mmolv.h.bar）） even at high temperature （70 ℃）, and produced high molecular weight polymers with unimodal molecular weight distributions, indicating the polymerization took place in a single-site nature. This result may be attributed to benefits of introduction of second-row donor atoms for adjusting charge density of the vanadium centers. In addition, these complexes also exhibited high catalytic activities for ethylene/1-hexene copolymerization. Catalytic activity, comonomer incorporation and polymer molecular weight can be controlled in a wide range by the variation of catalyst structure and the reaction parameters such as A1/V molar ratio, comonomer feed concentration and polymerization reaction temperature.
基金Supported by the Ministry of Science and Technology of China(No. 2005CB221408)the National Natural Science Founda-tion of China(Nos. 20423002, 20571061)Key Scientific Project of Fujian Province, China(No. 2005HZ01-3)
文摘Precursor decomposition was used for the preparation of VTeO/SBA-15 catalyst for the selective oxidation of propane to acrolein. The catalyst shows a better performance compared with those prepared by conventional impregnant method. A yield of 9.3% of acrolein was achieved with 2% V loadings at 500 ℃. XRD, N2-adsorption, H2-TPR, Py-IR and XPS measurements were used to unclose the relationship between the structure and performance of the catalyst.
基金financially supported by the National Natural Science Foundation of China(No.20734002)
文摘Mono salicylaldiminato vanadium（Ⅲ） complexes （1a-1f） [RN = CH（ArO）]VC12（THF）2 （Ar = C6H4 （1a-1e）, R = Ph, 1a; R = p-CFaPh, 1b; R = 2,6-Me2Ph, 1c; R = 2,6-iPrEPh, 1d; R = eyclohexyl, 1e; Ar = C6HEtBU2（2,4）, R = 2,6-iPrEPh, 1f） and bis（salicylaldiminato） vanadium（III） complexes （2a-2f） [RN ： CH（ArO）]EVCI（THF）x （Ar = C6H4 （2a-2e）, x = 1 （2a-2e）, R = Ph, 2a; R = p-CF3Ph, 2b; R = 2,6-Me2Ph, 2c; R = 2,6-iPr2Ph, 2d; R = cyclohexyl, 2e; Ar = C6HEtBU2（2,4）, R = 2,6-iPrEPh, x = 0, 2f） have been evaluated as the active catalysts for ethylene/1-hexene copolymerization in the presence of Et2A1C1. The ligand substitution pattern and the catalyst structure model significantly influenced the polymerization behaviors such as the catalytic activity, the molecular weight and molecular weight distribution of the copolymers etc. The highest catalytic activity of 8.82 kg PE/（mmolv.h） was observed for vanadium catalyst 2d with two 2,6-diisopropylphenyl substituted salicylaldiminato ligands. The copolymer with the highest molecular weight was obtained by using mono salieylaldiminato vanadium catalyst 1 f having ligands with tert-butyl at the ortho and para of the aryloxy moiety.
基金Project(2006AA06Z130)supported by the Hi-tech Research and Development Program of ChinaProject(2007GA010)supported by Yunnan Provincial Science and Technology Agency
文摘Extraction of vanadium from black shale was attempted in pressure acid leaching.The chemical components of the sample obtained from Guizhou Province of China show that it contains 3.258%V2O5,52.880%SiO2 and 16.140%Al2O3.Phase analyses of vanadium indicates vanadium mainly exists in the free oxide and mica.Vanadium contents in the two phases are 18%and 53%, respectively.The contents of V3 +,V 4+and V 5+are almost equal.Under the optimum parameters of one-step leaching(reaction time of 3 h,sulfuric addition of 25%,temperature of 150℃,liquid to solid ratio of 1.2 mL/g,catalyst(FeSO4)addition of 5%and size of 85%particle 0.074 mm),about 77%of vanadium is recovered.After two-step countercurrent leaching,the leach recovery of vanadium can reach above 90%.Air replacing oxygen is completely feasible.The impurity metals can dissolve into solution in different degrees.
