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1.
Levyne-type zeolites were synthesized from gels of initial compositions 4.5Na2O-6MeQI-xAl2O3 30SiO2-500H2O, with MeQ = methylquinuclidinium and 0.6 ≤ x ≥ 3 at 150 ≤ t ≥ 190 °C. The 29Si NMR spectra show the presence of two crystallographically different sites in the structure. The 27Al NMR spectra also suggest the presence of two different tetrahedral Al atoms incorporated in the structure. A rather high amount of defect groups SiOM and Si(OM)2 with M = MeQ, Na and/or H are present in the precursor samples. The Si(OM)2 groups are eliminated during calcination, and a certain amount of SiOM still persists after calcination. The combined 13C NMR and thermal analysis data allowed one to interpret the nature of the two different types of MeQ+ ions occluded in the levyne channels.  相似文献   

2.
Eight different molybdenum compounds were tested in the catalysts of ring-opening polymerization (ROP) of ε-caprolactone (CL). All homopolymerizations were conducted in bulk at 150 °C using a CL/molybdenum compound molar ratio of 200. Ammonium decamolybdate (NH4)8[Mo10O34] comes to be the best catalyst for ROP, based on its selectivity, short reaction times (2 h) and high conversions (98%). Aliphatic copolyesters with acid-funtional asymetric telechelic architecture -hydroxyl-ω-(carboxylic acid) (HA) were synthesized from lactones -such as CL, δ-valerolactone (VL) and γ-butyrolactone (BL)- by ring-opening copolymerization. HA-copolyesters, namely HA-poly(ε-caprolactone-co-γ-butyrolactone) (HA-PCB), HA-poly(δ-valerolactone-co-γ-butyrolactone) (HA-PVB) and HA-poly(ε-caprolactone-co-δ-valerolactone) (HA-PCV), were obtained at 150 °C in 2 h using ammonium decamolybdate as catalyt and water as initiator. A control of the degree of polymerization (DP, measured by NMR) can be achieved in the range between 6 and 24 for HA-PCB and HA-PCV, based on the initial monomer/initiator ratio. DP shows a linear dependence with M/H2O ratio (where M=CL+(BL or VL)) in this range. The nature of hydroxyl and carboxylic acid end groups of HA-copolyesters was determined by 1H and 13C NMR. Finally, HA-poly(ε-caprolactone-block-δ-valerolactone) (HA-PCbV) was successfully prepared by sequential copolymerization of HA-poly(ε-caprolactone) with VL and characterized by 1H and 13C NMR, GPC and MALDI-TOF.  相似文献   

3.
Steady-state isotopic transient kinetic analysis (SSITKA) experiments coupled with mass spectrometry were performed for the first time to study essential mechanistic aspects of the water–gas shift (WGS) reaction over alumina-supported Pt, Pd, and Rh catalysts. In particular, the concentrations (μmol g−1) of active intermediate species found in the carbon-path from CO to the CO2 product gas (use of 13CO), and in the hydrogen-path from H2O to the H2 product gas (use of D2O) of the reaction mechanism were determined. It was found that by increasing the reaction temperature from 350 to 500 °C the concentration of active species in both the carbon-path and hydrogen-path increased significantly. Based on the large concentration of active species present in the hydrogen-path (OH/H located on the alumina support), the latter being larger than six equivalent monolayers based on the exposed noble metal surface area (θ > 6.0), the small concentration of OH groups along the periphery of metal-support interface, and the significantly smaller concentration (μmol g−1) of active species present in the carbon-path (adsorbed CO on the noble metal and COOH species on the alumina support and/or the metal-support interface), it might be suggested that diffusion of OH/H species on the alumina support towards catalytic sites present in the hydrogen-path of reaction mechanism might be considered as a slow reaction step. The formation of labile OH/H species is the result of dissociative chemisorption of water on the alumina support, where the role of noble metal is to activate the CO chemisorption and likely to promote formate decomposition into CO2 and H2 products. It was found that there is a good correlation between the surface concentration and binding energy of CO on the noble metal (Pt, Pd or Rh) with the activity of alumina-supported noble metal towards the WGS reaction.  相似文献   

4.
H3PMo12O40 catalyst was chemically immobilized on the surface modified CMK-3 (SM-CMK-3) support as a charge compensating component, by taking advantage of the overall negative charge of [PMo12O40]3−. The supported H3PMo12O40/SM-CMK-3 catalyst was characterized to have high surface area (≈1000 m2/g) and relatively large pore volume (0.83 cm3/g). The H3PMo12O40/SM-CMK-3 catalyst was applied to the vapor-phase 2-propanol conversion reaction. The H3PMo12O40/SM-CMK-3 catalyst exhibited higher 2-propanol conversion than the unsupported H3PMo12O40 and the impregnated H3PMo12O40 on CMK-3. Furthermore, the PMo12/SM-CMK-3 catalyst showed the enhanced oxidation activity (acetone formation) and the suppressed acid catalytic activity (propylene formation) compared to the other two catalysts. It is believed that [PMo12O40]3− species were chemically and finely immobilized on the SM-CMK-3 support as charge matching species, and thus, the PMo12/SM-CMK-3 catalyst showed an excellent oxidation activity.  相似文献   

5.
A new organic–inorganic hybrid mesoporous zirconium oxophenylphosphate (ZPP-1) has been synthesized hydrothermally at 443 K by using phenylphosphonic acid (PPA) as phosphorus source in absence of any structure directing agent. Powder XRD, TEM, FE SEM, N2 sorption, CHN and ICP-AES chemical analyses, 13C CP/MAS and 31P MAS NMR, UV–visible and FT IR spectroscopic tools and thermal analysis were employed to characterize this novel material. XRD, N2 sorption and TEM image analysis suggested the existence of multi-lamellar structure of the pore wall with large micropores and mesopores having peak maximums of ca. 1.5 and 5.0–6.0 nm, respectively in this ZPP-1 material. Interestingly, this hybrid material showed very high thermal stability together with retention of nanostructure and phenyl group when heated upto 723 K. ZPP-1 showed fairly high H2 adsorption capacity under atmospheric pressure at 77 K. Possible templating role played by the framework phenyl groups has been discussed.  相似文献   

6.
Methylation of toluene (in one case benzene) with methanol has been investigated over four different zeolites: Small and large crystal ZSM-5, dealuminated mordenite and zeolite beta. The feed ratio methanol/arene was varied over a wide range, mostly >1, using nitrogen or helium as carrier gas. A rather high space velocity was employed (WHSV (methanol + arene): 5–35 h−1). The reaction temperature was 350°C or 375°C. A parallel set of experiments was performed using 13C methanol (99% 13C). The products were analyzed by on-line gas chromatography using a GC–MS system allowing determination of isotopic composition of the more important products, i.e., ethene, propene and the arenes when 13C methanol was employed, otherwise a FID was used. The goal was to obtain mechanistic information, and no attempt has been made to optimize for any particular reaction product.

The experiments showed that ethene and propene were isotopically mixed, containing 50–75% 13C. The 25–50% 12C atoms coming from the reactant arene. Over all catalysts the arene was, when fed alone, essentially inert with 0.5% or less conversion, giving neither ethene nor propene in measurable quantities. The isotopic distribution in ethene was indistinguishable from a random distribution. Propene, although being close to, displayed some deviation from randomness. The 12C/13C isotopic ratio in propene was equal to that in ethene, and they both varied with the methanol/arene ratio in the feed, but much less so than the variation in feed composition.

The results support a pool mechanism where the catalytic activity for converting methanol to hydrocarbons is connected with the presence of adsorbates in the zeolite cavities which add methanol and split off product molecules, notably ethene and propene. Formation of ethene by reaction between C1 species is at best a minor reaction. While formation of propene may take place by a homologation/cracking mechanism, this route was of minor importance here.

Polymethylbenzenes which were formed in many cases displayed a pronounced isotopic scrambling, containing up to six 13C atoms in the benzene ring. Molecules with fewer 13C atoms than the number of added methyl groups were also identified.  相似文献   


7.
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   

8.
A novel tetrapolymer(TP) consisting of carboxylate, sulphonate, phosphonate and sulfur dioxide based comonomers was synthesized using Butler cyclopoymerization technique. The synthesized tetrapolymer was characterized using FTIR,1 H-NMR,~(13)CNMR and elemental analysis. The performance of the tetrapolymer as a corrosion inhibitor for St37 carbon steel in 15% HCl and 15% H_2SO_4 acid media was assessed using electrochemical impedance spectroscopy(EIS), linear polarization resistance(LPR), potentiodynamic polarization(PDP) and electrochemical frequency modulation(EFM) techniques. The influence of addition of a small amount of KI on the corrosion inhibition efficiency of TP was also assessed. Results obtained showed that the tetrapolymer moderately inhibited the corrosion of St37 steel in the acid media with protection efficiency of 79.5% and 61.1% at the optimum concentration of 1000 mg·L~(-1) studied in HCl and H_2SO_4 media respectively. On addition of 5 mmol·L~(-1) KI to the optimum tetrapolymer concentration, the protection efficiency was upgraded to 90.6% and 93.5% in HCl and H_2SO_4 environment, respectively. The enhanced performance of the polymer in the presence of KI is due to synergistic action deduced from synergism parameter(S1) which was found to be greater than unity.The tetrapolymer afforded the corrosion inhibition of St37 steel in the acid media by virtue of adsorption of the polymer molecules on the steel surface which was confirmed by ATR-FTIR analysis of the adsorbed film extracted from the steel surface. TP + KI formed complex with St37 steel surface in H_2SO_4 solution but not in HCl solution.  相似文献   

9.
We synthesized high-quality and oriented periodic mesoporous organosilica (PMO) monoliths through a solvent evaporation process using a wide range of mole ratios of the components: 0.17–0.56 1,2-bis(triethoxysilyl)ethane (BTSE): 0.2 cetyltrimethylammonium chloride (CTACl): 0–1.8 × 10−3 HCl: 0–80 EtOH: 5–400 H2O. X-ray diffraction (XRD) patterns and transmission electron microscopy (TEM) images indicated that the mesoporous channels within the monolith samples were oriented parallel to the flat external surface of the PMO monolith and possessed a hexagonal symmetry lattice (p6mm). The PMO monolith synthesized from a reactant composition of 0.35 BTSE: 0.2 CTACl: 1.8 × 10−6 HCl: 10 EtOH: 10 H2O had a pore diameter, pore volume, and surface area – obtained from an N2 sorption isotherm – of 25.0 Å, 0.96 cm3 g−1 and 1231 m2 g−1, respectively. After calcination at 280 °C for 2 h in N2 flow, the PMO monolith retained monolith-shape and mesostructure. Pore diameter and surface area of the calcined PMO monolith sample were 19.8 Å, 0.53 cm3 g−1 and 1368 m2 g−1, respectively. We performed 29Si and 13C CP MAS NMR spectroscopy experiments to confirm the presence of Si–C bonding within the framework of the PMO monoliths. We investigated the thermal stability of the PMO monoliths through thermogravimetric analysis (TGA). In addition, rare-earth ions (Eu3+, Tb3+ and Tm3+) were doped into the monoliths. Optical properties of those Eu3+, Tb3+ and Tm3+-doped PMO monoliths were investigated by photoluminescence (PL) spectra to evaluate their potential applicability as UV sensors.  相似文献   

10.
The precursor of zirconium oxide is synthesized by the sol-gel method by reacting zirconyi chloride octahydrate (ZrOCl2 8H2O) and citric acid in ammonia solution. The ionized complex compounds (R(COO-+NH4)3) were first formed from the reaction of complex agent (citric acid) and ammonium hydroxide. Zirconyi chloride octahydrate first hydrolyzed to produce zirconium tetranuclear complex molecule [Zr4(OH)8(OH2)l6(—OOC)3R]8+ which subsequently produced a large complex molecule ([Zr4(OH)5(OH2)|6(—OOC)3R)5+ or [Zr4(OH)8(OH2)13(—OOC)3R]5+) through the polymerization of zirconium tetramer with the ionized complex agent. The effect of the reaction conditions on the precursor solution's viscosity and average particle size were investigated in order to understand the kinetics of the reaction. A rational reaction mechanism is proposed satisfactorily to explain the formation and growth of the particles and viscosity of the sol.  相似文献   

11.
Focused beam reflectance measurement (FBRM) and 13C nuclear magnetic resonance (13C NMR) analysis were used to study the precipitation process of CO2-loaded potassium glycinate (KGLY) solutions at different CO2 loadings, during the addition of ethanol as an antisolvent at a rate of 10 mL·min−1. The volume ratio of ethanol added to the KGLY solution (3.0 mol·L−1, 340 mL) ranged from 0 to 3.0. Three solid-liquid-liquid phases were formed during the precipitation process. The FBRM results showed that the number of particles formed increased with CO2 loading and ethanol addition for CO2-unsaturated KGLY solutions, whilst for CO2-saturated KGLY solution it first increased then decreased to a stable value with ethanol addition. 13C NMR spectroscopic analysis showed that the crystals precipitated from the CO2-unsaturated KGLY solutions consisted of glycine only, and the quantity crystallised increased with CO2 loading and ethanol addition. However, a complex mixture containing glycine, carbamate and potassium bicarbonate was precipitated from CO2-saturated KGLY solution with the maximum precipitation percentages of 94.3%, 31.4% and 89.6%, respectively, at the ethanol volume fractions of 1.6, 2.5 and 2.3.  相似文献   

12.
The 13C-tracer results from the introduction of 13C2H4 into syngas prior to conversion with a rhodium catalyst have been used to support a surface vinyl mechanism for Fischer–Tropsch synthesis. The results were first interpreted by a mechanism that involved a decrease in 13C species on the surface as the carbon number increased. This model is shown to be incorrect. Considering only the 13C-labeled products, the data are consistent with earlier tracer studies showing that the added 13C2H4 initiates chains.  相似文献   

13.
The formation process of diamond from supercritical H2O–CO2 fluid was studied using 13C-graphitic carbon and oxalic acid dihydrate, (COOH)2·2H2O, as starting materials under a diamond stable high pressure–high temperature (HP–HT) condition of 7.7 GPa and 1600°C. The exchange reaction between 13C-graphitic carbon and 12CO2 in the supercritical H2O–CO2 fluid, which was first formed by the decomposition of oxalic acid dihydrate, occurred very rapidly and became nearly equilibrated after 6 h. At the same time, graphite was recrystallized and coexistent with the fluid until traces of diamond were first observed after 8 h. All graphite transformed into diamond after 17 h, showing that a considerably long induction time was present for the formation of diamond in this fluid system.  相似文献   

14.
A sample of kerogen from Aleksinac oil shale was examined by high-resolution solid-state 13C n.m.r. spectroscopy. The presence and relative proportions of kerogen structural units were estimated using a combination of NQS and T1C methods with a peak-synthesis technique applied to the 13C CP—MAS spectrum. Relaxation parameters from these experiments were used to estimate differences in relative ‘mobility’ of various structural units. The kerogen was found to be highly aliphatic and to contain 79% long-chain aliphatic plus alicyclic structures, as well as 9% aromatic structures. These findings are in good agreement with the characterization of the same kerogen from its oxidation products.  相似文献   

15.
A commercial Co---Mo/Al2O3 catalyst was labeled with the radioisotope 35S in hydrodesulfurization (HDS) of 35S-labeled dibenzothiophene (35S-DBT) in a high-pressure flow reactor at 50 kg/cm2. Then, HDS of 4-methyldibenzothiophene (4-MDBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) or sulfur exchange of H2S were carried out on the labeled catalyst at 50 kg/cm2 and 260–360°C. The amounts of labile sulfur participating in the reaction were determined from the radioactivity of 35S---H2S released from the 35S-labeled catalyst. In the HDS reactions, the amount of labile sulfur participating in the reaction decreased in the order: DBT> 4-MDBT> 4,6-DMDBT. In the sulfur exchange reaction with H2S, the adsorption of H2S on the catalyst reached saturation above a H2S partial pressure of 0.36 kg/cm2. It was suggested that the release of H2S from the labile sulfur may be the rate determining step of the HDS reaction.  相似文献   

16.
We report the kinetic parameters for the water–gas shift (WGS) reaction on Pt catalysts supported on ceria and alumina under fuel reformer conditions for fuel cell applications (6.8% CO, 8.5% CO2, 22% H2O, 37.3% H2, and 25.4% Ar) at a total pressure of 1 atm and in the temperature range of 180–345 °C. When ceria was used as a support, the turnover rate (TOR) for WGS was 30 times that on alumina supported Pt catalysts. The overall WGS reaction rate (r) on Pt/alumina catalysts as a function of the forward rate (rf) was found to be: r = rf(1 − β), where rf = kf[CO]0.1[H2O]1.0[CO2]−0.1[H2]−0.5, kf is the forward rate constant, β = ([CO2][H2])/(Keq[CO][H2O]) is the approach to equilibrium, and Keq is the equilibrium constant for the WGS reaction. The negative apparent reaction orders indicate inhibition of the forward rate by CO2 and H2. The surface is saturated with CO on Pt under reaction conditions as confirmed by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The small positive apparent reaction order for CO, in concert with the negative order for H2 and the high CO coverage is explained by a decrease in the heat of adsorption as the CO coverage increases. Kinetic models based on redox-type mechanisms can explain the observed reaction kinetics and can qualitatively predict the changes in CO coverage observed in the DRIFTS study.  相似文献   

17.
Polymerizations of cyclotrimethylenecarbonate (TMC) with SnCl4, SnBr4 were and SnI4 were conducted in bulk. The reaction time, the temperature and the monomer/initiator (M/I) ratio were varied, and the influence of these parameters on yields and molecular weights was investigated. Yields above 90% were obtained with all these initiators, but the highest molecular weights (Mw ≈ 1.5 × 105) resulted from SnI4-initiated polymerizations. SnI4 has the additional advantage that the polycarbonates were free of ether groups when prepared at moderate temperatures (e.g. 60°C). In contrast, SnCl4 and SnBr4 cause partial decarboxylation even at 60°C, and at higher temperatures up to 20 mol% of the carbonate groups may be replaced by ether linkages. Furthermore, mechanistic studies were conducted. SnCl4 and SnBr4 form solid 1:2 complexes with TMC at 20–25°C. Infra-red, 1H and 13C nuclear magnetic resonance (n.m.r.) spectroscopies indicate complexation at the carbonyl oxygen. Kinetic measurements of polymerizations in solvents of different polarity suggest cationic polymerization mechanisms. In addition to CH2---OH, CH2Cl and CH2Br end groups were detected by 1H n.m.r. spectroscopy. The endgroup analyses of reaction mixtures and isolated poly(TMC) support the assumption of a cationic polymerization mechanism.  相似文献   

18.
The structure of initial, ultimate and inner chain units in polybutadiene produced with NdCl3. 3(i-PrOH)---HAl(i-Bu)2was studied by means of 13C nuclear magnetic resonance spectroscopy. Initial units are shown to be predominantly of trans-CH3CH=CHCH2--- structure. Conversely, 90% of inner units have cis configuration. Ultimate units obtained by quenching with H2O (D2O) are predominantly of 1,2 structure. On the basis of the data obtained, the polymerization mechanism was discussed.  相似文献   

19.
The production and decay of singlet molecular oxygen (1O2) in TiO2 photocatalysis were investigated by monitoring its phosphorescence under various reaction conditions. First, the effects of additives such as KBr, KSCN, KI, H2O2, and ethanol on the amount of 1O2 produced by photo excitation of P25 TiO2 were measured. The same additives were employed to investigate the effect on the amount of O2 produced. Comparison between the effects on 1O2 and O2 suggested that 1O2 is formed by the electron transfer mechanism, the reduction of molecular oxygens to O2 by photogenerated electrons and the subsequent oxidation of O2 to 1O2 by photogenerated holes. The formation of 1O2 decreased at pH < 5 and pH > 11, indicating that the intermediate O2 is stabilized at the terminal OH site of the TiO2 surface in the pH range of 5 < pH < 11. Eighteen commercially available TiO2 photocatalysts were compared on the formation of 1O2 and O2 in an aqueous suspension system. The formation of 1O2 was increased with decreasing size of TiO2 particles, indicating that a large specific surface area causes a higher possibility of reduction producing O2 and then a large amount of 1O2 is formed. The difference in the crystal phase (rutile and anatase) did not affect the formation of 1O2.  相似文献   

20.
以过氧化氢氧化再生纤维素(GC)制备羧基再生纤维素(OGC),表征OGC结构变化及其对阻燃和吸附性能影响机理。通过碱泡预处理能有效提高GC比表面积,增加反应效率,获得羧基含量达15.6%的OGC。FT-IR和13C NMR表征结果说明OGC葡萄糖基环上的C6位伯羟基能被选择性氧化成羧基。随着羧基含量的提高,OGC无定形部分溶解而提高其结晶度,晶型则无显著变化,OGC的热分解温度下降,但是成炭率显著提高。当添加6.25%OGC为成炭剂用于环氧树脂膨胀型阻燃时,氧指数达到27.2,阻燃等级为V0。以火焰原子吸收分光光度法测定结果表明,当羧基含量为15.6%,OGC对铅和铜离子吸附量分别提高14倍和3.5倍,其原因在于氧化改性能显著提高OGC的比表面积和容积率,增加吸附容量。研究结果说明以过氧化氢氧化制备的OGC在阻燃成炭剂以及金属离子吸附领域中具有良好的应用前景。  相似文献   

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