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1.
Mnica Carcuchinski Haag Joo Henrique Zimnoch Dos Santos Jairton Dupont Argimiro Resende Secchi 《应用聚合物科学杂志》2000,76(3):425-438
A mathematical model for the homogeneous terpolymerization of ethylene–propylene–diene (EPDM) in a semibatch reactor using Et(Ind)2ZrCl2/MAO as a catalyst system was developed and reported herein. In this study, we developed a kinetic model in order to explain the catalyst and EPDM properties such as catalyst activity, weight‐average molecular weight, and terpolymer composition, which were experimentally and theoretically obtained. For this system, a lower E/P feed ratio leads to a lower molecular weight and a broader initial molecular weight distribution, while the increase in diene concentration leads to a decrease in the catalyst activity without broadening the MWD of the resulting polymers. The proposed model accounts for these experimental trends and for some data in the literature. 相似文献
2.
M. C. Haag J. H. Z. Dos Santos F. C. Stedile M. A. De Araújo J. Dupont I. J. R. Baumvol 《应用聚合物科学杂志》1998,68(4):535-541
A series of ethylene–propylene-2-ethylidenebicyclo[2.2.1]hept-5-ene terpolymers have been prepared using the VOCl3/Al2Et3Cl3 catalyst under various initial Al/V ratios and diene concentrations. The V/C and Al/V ratios in EPDM films were determined by Rutherford backscattering spectrometry. The concentration of incorporated vanadium increases with the increase of the iodine number, i.e., with the number of double bonds in the polymer. However, the concentration of incorporated V in the terpolymers remains relatively low, which is attributed to the small percentage of V(III) active species due to the presence of the diene. On the other hand, the Al/V molar ratio in the terpolymers was seen to be roughly constant (between 6 and 8), independent of the iodine number and of the initial Al/V molar ratio in the reaction mixture. The polymerization yield was seen to increase with the augmentation of the initial Al/V ratio and of the diene concentration, until reaching a maximum of about 500 g polymer/g V. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 535–541, 1998 相似文献
3.
Monoclinic Li3V2−xAlx(PO4)3 with different Al3+ doping contents (x = 0, 0.05, 0.08, 0.10 and 0.12) have been prepared by a facile aluminothermal reaction. Aluminum nanoparticles have been used as source for Al3+ and nucleus for Li3V2−xAlx(PO4)3 nucleation as well as reducing agent in the aluminothermal strategy. The products were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and electrochemical methods. The XRD results show that the as-obtained Li3V2−xAlx(PO4)3 has a phase-pure monoclinic structure, irrespective of the Al3+ doping concentration. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) results reveal that the charge-transfer resistance of the Li3V2(PO4)3 is reduced and the reversibility is enhanced after V3+ substituted by Al3+. In addition, The Li3V2−xAlx(PO4)3 phases exhibit better cycling stability than the pristine Li3V2(PO4)3. 相似文献
4.
Free-radical solution terpolymerization of acrylamide, acrylic acid, and acrylonitrile was carried out in a mixture of dimethylformamide and water (60 : 40,v/v) at 85°C using benzoyl peroxide as the initiator. The polymers were characterized by elemental analysis, IR, 1H-NMR, TGA, and viscosity measurements. Elemental analysis data were used to evaluate the terpolymer composition. The reactivity ratios were determined by Fineman–Ross and Kelen–Tudos methods. The reactivity ratios (r) for the copolymerization of (1) acrylic acid + acrylonitrile with (2) acrylamide was found to be r1 = 0.86 ± 0.09 and r2 = 1.93 ± 0.03, respectively, by the Kelen–Tudos method. The Fineman–Ross method yielded a value of r1 = 0.86 ± 0.05 and r2 = 1.94 ± 0.09, respectively. The activation energy values for various stages of decomposition were calculated from TGA analysis. Voluminosity (VE) and the shape factor (ν) were also computed from the viscosity measurements in different ratios of the solvent mixture. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 217–228, 1998 相似文献
5.
(Ind)2ZrCl2 catalyst was synthesized and used for copolymerization of ethylene and propylene (EPR) and terpolymerization of ethylene propylene and 5‐ethyldiene‐2‐norbornene (ENB). Methylaluminoxane (MAO) was used as cocatalyst. The activity of the catalyst was higher in copolymerization of ethylene and propylene (EPR) rather than in terpolymerization of ethylene, propylene and diene monomers. The effects of [Al] : [Zr] molar ratio, polymerization temperature, pressure ratio of ethylene/propylene and the ENB concentration on the terpolymerization behavior were studied. The highest productivity of the catalyst was obtained at 60°C, [Al] : [Zr] molar ratios of 750 : 1 and 500 : 1 for copolymerization and terpolymerization, respectively. Increasing the molar ratio of [Al] : [Zr] up to 500 : 1 increased the ethylene and ENB contents of the terpolymers, while beyond this ratio the productivity of the catalyst dropped, leading to lower ethylene and ENB contents. Terpolymerization was carried out batchwise at temperatures from 40 to 70°C. Rate time profiles of the polymerization were a decay type for both copolymerization and terpolymerization. Glass transition temperatures (Tg) of the obtained terpolymers were between ?64 and ?52°C. Glass transition temperatures of both copolymers and terpolymers were decreased with increased ethylene content of the polymers. Dynamic mechanical and rheological properties of the obtained polymers were studied. A compounded EPDM showed good thermal stability with time. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011 相似文献
6.
Elastic,mechanical, electronic,and defective properties of Zr–Al–C nanolaminates from first principles
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Changying Wang Han Han Yuanyuan Zhao Wei Zhang Yongliang Guo Cuilan Ren Guangli Zeng Qing Huang Ping Huai 《Journal of the American Ceramic Society》2018,101(2):756-772
By means of first principles calculations, Zr–Al–C nanolaminates have been studied in the aspects of chemical bonding, elastic properties, mechanical properties, electronic structures, and vacancy stabilities. Although the investigated Zr–Al–C nanolaminates show crystallographic similarities, their predicated properties are very different. For (ZrC)nAl3C2 (n = 2, 3, 4), the Zr–C bond adjacent to the Al–C slab with the C atom intercalated in the Zr layers is the strongest, but the one with the C atom intercalated between the Zr layer and Al layer is the weakest. In contrast, the situation for (ZrC)nAl4C3 (n = 2, 3) is just the opposite. For Zr–Al–C nanolaminates, the calculated bulk, shear and Young's modulus increase in the sequence of Zr2AlC < Zr3AlC2 < Zr2Al4C5 < Zr3Al4C6 < Zr2Al3C4 < Zr3Al3C5 < Zr4Al3C6. The (ZrC)nAl3C2 (n = 2, 3, 4) series exhibit the most outstanding elastic properties. In the presence of the external pressure, the bulk and shear moduli exhibit a linear response to the pressure, except for Zr2AlC and Zr3AlC2, both of which belong to the so‐called MAX phases. The two materials also exhibit very distinct properties in the strain‐stress relationship, electronic structures and vacancy stabilities. As the intercalated Al layers increase, the formation energy of VZr and VAl increases, while the formation energy of VC decreases. 相似文献
7.
Soohyun Bae Soo Min Kim Kyung Dong Lee Young Do Kim Sungeun Park Yoonmook Kang Hae-Seok Lee Donghwan Kim 《Israel journal of chemistry》2015,55(10):1075-1080
Al2O3 layers fabricated with atomic layer deposition (ALD) show high levels of surface passivation on p- and n-type silicon wafers. In order to form front and rear electrodes, Al2O3 layers should undergo a firing process at a high peak temperature. Therefore, the Al2O3 layer must be stable under these conditions to maintain a high level of surface passivation during the firing process. In this study, Al2O3 layers fabricated with ALD were pre-annealed to enhance their thermal stability during the firing process. From quasi-steady state photoconductance (QSSPC) measurements, the difference between the implied Voc values of the pre-annealed and fired samples was found to be smallest (3 mV) when the sample was pre-annealed at 620 °C. The surface recombination rate calculated from capacitance-voltage (C-V) measurements of metal-Al2O3-Si (metal-insulator-semiconductor) structures was shown to be low when the sample was pre-annealed at 600–650 °C. Thus, firing stability was achieved with pre-annealing at 620 °C by reducing the surface recombination rate. We conclude that it is necessary to pre-anneal the Al2O3 passivation layer at this specific temperature to reduce the degradation of the passivation quality of Al2O3 after the firing process. 相似文献
8.
Hamdy F. M. Mohamed 《应用聚合物科学杂志》2008,108(2):1307-1313
Coincidence Doppler broadening of annihilation radiation (CDBAR) and Vickers hardness techniques were performed to study pure Al2O3, pure polyvinyl chloride (PVC), and doped PVC with different concentrations of Al2O3 (10–50%). The CDBAR ratio curves with respect to pure PVC were presented and reflect the momentum distribution of all the samples. The peak around 14.5 ×10?3 moC in the CDBAR ratio curves suggests a large contribution of positron annihilation with the Al2O3. There is a linear correlation between the height of this peak and the Al2O3 concentration. The S‐ and W‐parameters were extracted from the CDBAR spectra and increase with increasing the Al2O3 concentration showing discontinuity at 30% of Al2O3 concentration on PVC. The present data confirmed that there is no positronium formation in pure Al2O3 as a result of smaller S‐parameter. The Vickers hardness increases with increasing the Al2O3 concentration in PVC showing a linear dependence with two different slopes depend on the Al2O3 concentration range. A correlation between the Vickers hardness (macroscopic data) and the W‐parameter (microscopic data) was observed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
9.
In this study, the NO reduction by NH3 over V2O5/NPTiO2–Al2O3 (nanoparticles) and V2O5/NTiO2–Al2O3 (nanotubes) catalysts synthesized by the sol–gel method with 10 and 5 wt.% of Al2O3 and V2O5, respectively, is reported. The V2O5/NPTiO2–Al2O3 and V2O5/NTiO2–Al2O3 catalysts showed remarkable conversion, high acidity, structure stability, N2 selectivity and a high resistance to deactivation in the presence of 10 vol.% of H2O within the 200 to 500 °C temperature interval. The nanostructured catalysts developed in this work are an excellent alternative to improve the SCR–NH3 process, both expanding its operation window and preventing deactivation by H2O at high temperatures. 相似文献
10.
Takahiro Ohkubo Eiji Tsuchida Kenzo Deguchi Shinobu Ohki Tadashi Shimizu Toshiya Otomo Yasuhiko Iwadate 《Journal of the American Ceramic Society》2018,101(3):1122-1134
It remains a challenge to establish structural models of multicomponent oxide glass systems. In this study, we have investigated 68.3SiO2–16.1B2O3–4.2Al2O3–11.4Na2O glass and melt structures by ab initio molecular dynamics (AIMD) simulations. The atomic configurations obtained from AIMD simulations were validated against 17O solid‐state NMR spectrum under 24.0 T and neutron diffraction data, and excellent agreement was achieved. The bond lengths, angles, and coordination geometries were statistically analyzed for each atomic species. Here we particularly address the role of minor atomic species such as five‐coordinate Si (SiV) and Al (AlV). The SiV–O bond lengths and O–SiV–O angle distribution in the glass indicated 1.718 Å and three peaks at 90°, 120°, and 175°, which are assigned to a coordination geometry of the trigonal bipyramidal structure. Ring statistic analysis revealed that SiV and AlV were found to preferentially contribute to the formation of small ring sizes. 相似文献
11.
Basude Manohar Benjaram M. Reddy 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1998,71(2):141-146
Ammoxidation of 3-picoline to nicotinonitrile was investigated on vanadium phosphorus oxide (VPO), VPO/SiO2 and additive atom (Cu, Zr, Mn and Co) incorporated VPO catalysts under atmospheric pressure and at 673 K. For the purpose of comparison a conventional V2O5–MoO3/Al2O3 catalyst was also studied under identical conditions. These catalysts were characterized by means of X-ray diffraction, electron spin resonance, infrared, ammonia chemisorption and BET surface area methods. The VPO-based catalysts show better performance than the V2O5–MoO3/Al2O3 catalyst. Further, the VPO/SiO2 and VPO catalysts exhibit better conversion and product selectivities than the additive-containing VPO catalysts. Better activity of VPO and VPO/SiO2 catalysts was related to their high active surface area, higher surface acidity and lower oxidation state of vanadium. The redox couple between (VO)2P2O7 (V4+) and αI-VOPO4 (V5+) phases appears to be responsible for the ammoxidation activity of VPO catalysts. © 1998 SCI. 相似文献
12.
Sung-Wook Han Won-Moon Choi Jong-Gu Park Chang-Sik Ha Soon-Ki Kwon Won-Jei Cho 《应用聚合物科学杂志》1998,67(10):1721-1727
The graft terpolymerization of methyl vinyl ketone (MVK) and styrene (St) onto ethylene–propylene–diene terpolymer (EPDM) was carried out under various polymerization conditions. The synthesized graft terpolymer, MVK–EPDM–St (MVES), was identified by infrared (IR) spectroscopy. The effects of monomer concentration, mole ratio of MVK to St, reaction time, reaction temperature, and initiator concentration on the graft terpolymerization were examined. Upon UV irradiation in the presence of oxygen, the MVES-containing carbonyl group showed photodegradable properties caused by Norrish type II reaction. The new IR characteristic peaks, such as carbonyl, vinyl, and hydroxy groups of the photodegraded MVES, increased with increasing UV irradiation time. The tensile strength and elongation at break of MVES after UV irradiation were lower than those of before UV irradiation. The color difference of the irradiated MVES was higher than that of EPDM. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1721–1727, 1998 相似文献
13.
Shailesh J. Patil 《Chemical Engineering Communications》2019,206(5):605-618
Jatropha oil is a promising nonedible feedstock for producing renewable diesel. In this work, the hydrotreatment processing of jatropha oil was investigated. Instead of using conventional alumina-supported Co–Mo, Ni–Mo, and Ni–W catalysts that need sulfidation pretreatment, noble metals such as Pd and Ru were chosen. Trials were performed in an isothermal trickle-bed reactor and the reaction conditions were as follows: temperature 603–663?K, weight hourly space velocity (WHSV) 1 to 4/h, pressure 1.5–3?MPa, and H2/oil ratio 200–800 (v/v). Yield of n-C15 to n-C18 hydrocarbons was maximized (70.3 and 43.8% for Pd/Al2O3 and Ru/Al2O3, respectively) at the following conditions: T?=?663 K, WHSV?=?2/h, P?=?3?MPa, and H2/oil ratio?=?600 (v/v). Since Ru favored cracking reactions to a larger extent than Pd, the yield of C15 to C18 hydrocarbons over Ru/Al2O3 was lowered. Using simple first-order plots for oil conversion, activation energies for the hydrotreating process over Pd/Al2O3 and Ru/Al2O3 were found and they were equal to 109 and 121?kJ/mol, correspondingly. 相似文献
14.
《Catalysis communications》2010,11(15):2018-2022
Commercial Cu–ZnO–Al2O3 catalysts are used widely for steam reforming of methanol. However, the reforming reactions should be modified to avoid fuel cell catalyst poisoning originated from carbon monoxide. The modification was implemented by mixing the Cu–ZnO–Al2O3 catalyst with Pt–Al2O3 catalyst. The Pt–Al2O3 and Cu–ZnO–Al2O3 catalyst mixture created a synergetic effect because the methanol decomposition and the water–gas shift reactions occurred simultaneously over nearby Pt–Al2O3 and Cu–ZnO–Al2O3 catalysts in the mixture. A methanol conversion of 96.4% was obtained and carbon monoxide was not detected from the reforming reaction when the Pt–Al2O3 and Cu–ZnO–Al2O3 catalyst mixture was used. 相似文献
15.
Louise Olsson Miroslawa Abul-Milh Hanna Karlsson Edward Jobson Peter Thormählen Andreas Hinz 《Topics in Catalysis》2004,(1):85-90
Three model catalysts (Pt/Al2O3, Pt/TiO2, Pt/V2O5/TiO2) were examined in regard to their NO2 formation ability under a changing lean gas composition. The results show that the NO to NO2 oxidation function as well as the NO
x
reduction under lean gas conditions is affected by a change in the lean gas atmosphere. The NO oxidation activity also decreased with time, for Pt/Al2O3 and Pt/TiO2, and a possible explanation may be platinum oxide formation. This deactivation was not observed for Pt/V2O5/TiO2. 相似文献
16.
Shiao-Jung Chu Yu-Wen Chen 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1998,72(1):1-6
A series of beta zeolites with various SiO2/Al2O3 ratios has been synthesized. These samples were characterized with respect to crystallinity, particle size, acidity and sorption capacities of water, n-hexane and cyclohexane. The conversion of 1,3,5-trimethylbenzene (TrMB) was conducted in a fixed bed reactor at 493–743 K and atmospheric pressure. The conversion of 1,3,5-TrMB decreased with an increase in the SiO2/Al2O3 ratio of the zeolite. The zeolites with low SiO2/Al2O3 ratio favored the disproportionation and the zeolites with high SiO2/Al2O3 ratio favored the isomerization. These can be interpreted by the acid concentration of zeolite. In the isomerization, all zeolites produced more 1,2,4-TrMB than 1,2,3-TrMB. In the disproportionation, the selectivity of tetramethylbenzene (TeMB) was in the order of 1,2,3,5->1,2,4,5->1,2,3,4-TeMB. The concentration of 1,2,4,5-TeMB is greater than that at equilibrium. The results show that shape selectivity comes into effect. The reaction temperature and the reaction time on stream also affect the selectivity significantly due to coke formation in the zeolites. © 1998 SCI 相似文献
17.
Maria S. Avila Charito I. Vignatti Carlos R. Apesteguía V. Venkat Rao Komandur Chary Teresita F. Garetto 《Catalysis Letters》2010,134(1-2):118-123
Propane combustion was studied on Pt(0.4%)/V2O5–Al2O3 catalysts containing up to 20% V2O5. The density, strength and nature of surface acid sites were determined by TPD of NH3 and FTIR spectra of adsorbed pyridine. The sample acidity increased with the vanadium content, essentially because the addition of vanadium oxide generated Brønsted acid sites. The Pt dispersion as determined by H2 chemisorption increased with increasing V2O5 loading. The sample activity for propane combustion was evaluated through both conversion versus temperature (light-off curves) and kinetically-controlled conversion versus time catalytic tests. The propane combustion turnover rate on Pt/V2O5–Al2O3 increased with the amount of vanadium, probably because the intrinsic Pt oxidation activity increases with the sample acidity. 相似文献
18.
This paper reports an investigation on the structure-properties correlation of trivalent metal oxide (Al2O3)-doped V2O5 ceramics synthesized by the melt-quench technique. XRD patterns confirmed a single orthorhombic V2O5 phase formation with increasing strain on the doping of Al2O3 in place of V2O5 in the samples estimated by Williamson-Hall analysis. FTIR and Raman investigations revealed a structural change as [VO5] polyhedra converts into [VO4] polyhedra on the doping of Al2O3 into V2O5. The optical band gap was found in a wide semiconductor range as confirmed by UV–visible spectroscopy analysis. The thermal and conductivity behavior of the prepared samples were studied using thermal gravimetric analysis (TGA) and impedance analyzer, respectively. All the prepared ceramics exhibit good DC conductivity (0.22–0.36 Sm-1) at 400 ?C. These materials can be considered for intermediate temperature solid oxide fuel cell (IT-SOFC)/battery applications due to their good conductivity and good thermal stability. 相似文献
19.
Yi Zhong Ying Liu Jinwen Ye Na Jin Zifeng Lin 《Journal of the American Ceramic Society》2022,105(3):2277-2287
V2AlC and V4AlC3 are obtained in much milder conditions by a new facile approach using low-cost V–Al alloys and carbon black with the assistance of molten salts. Density functional theory (DFT) calculations show that our strategy is feasible and thermodynamically superior to the traditional method, with the following X-ray diffraction and Scanning Electron Microscopy fully revealing the phase and morphology evolutions of both reaction processes. Unreported formation mechanisms are revealed for the first time. Al8V5 transforms directly into V2AlC with both lattices perfectly overlapped due to the existence of multiple parallel planes between V2AlC and Al8V5 with consistent interplanar spacings, which leads to the overlapped phenomenon of the diffraction spots as well. For V4AlC3, an embedded structure of V2AlC–VC is first formed through an aluminum removing behavior in V2AlC layers, causing the increase of the VC content, and V4AlC3 is transformed by the embedded V2AlC–VC structure through diffusion and interface migration with a possible climb behavior of Frank partial dislocation. 相似文献
20.
《Applied Catalysis A: General》2001,205(1-2):173-182
Coking due to possible cracking reactions in a Ni–Mo/Al2O3 hydrotreatment catalyst was studied independently of the sulfur present. A model has been tested to predict the carbon concentration profiles obtained during the reaction. Simulated and experimental results are compared and several kinetic equations are tested in the simulation. The model predicts well the average carbon level in the catalytic bed and gives a slightly higher maximum carbon concentration. 相似文献