共查询到20条相似文献,搜索用时 31 毫秒
1.
The oxidation of CH 4 over Pt–NiO/δ-Al 2O 3 has been studied in a fluidised bed reactor as part of a major project on an autothermal (combined oxidation–steam reforming) system for CH 4 conversion. The kinetic data were collected between 773 and 893 K and 101 kPa total pressure using CH 4 and O 2 compositions of 10–35% and 8–30%, respectively. Rate–temperature data were also obtained over alumina-supported monometallic catalysts, Pt and NiO. The bimetallic Pt–NiO system has a lower activation energy (80.8 kJ mol −1) than either Pt (86.45 kJ mol −1) and NiO (103.73 kJ mol −1). The superior performance of the bimetallic catalyst was attributed to chemical synergy. The reaction rate over the Pt–NiO catalyst increased monotonically with CH 4 partial pressure but was inhibited by O 2. At low partial pressures (<30 kPa), H 2O has a detrimental effect on CH 4 conversion, whilst above 30 kPa, the rate increased dramatically with water content. 相似文献
2.
Two vinyl ether monomers with alkoxybiphenyl groups, 2-(4′-ethoxy-4-biphenyloxy)ethyl vinyl ether (EtOVE) and 2-(4′-hexyloxy-4-biphenyloxy)ethyl vinyl ether (HexOVE), were polymerized by living cationic polymerization reactions using either the hydrogen iodide/iodine (HI/I 2) or the hydrogen iodide/zinc iodide (HI/ZnI 2) initiator systems, or both. These initiators yield polymers with narrow molecular weight distributions (MWDs) and for comparison broad MWD polymers were also prepared by using the BF 3OEt 2 initiator. The thermal properties and phase transitions of these polymers were determined by differential scanning calorimetry, by visual observations of samples on a hot stage on a polarizing microscope, by polarized light transmission intensity measurements and by wide angle X-ray diffraction analysis. The polymer from EtOVE, P(EtOVE), with a weight average molecular weight,
, of less than about 8000 formed both smectic and nematic liquid crystalline, LC, phases after one heating cycle. In contrast, the polymer from this monomer which had an
of more than about 8000 exhibited only a nematic LC phase. For the polymer from HexOVE, P(HexOVE), both the narrow and broad MWD samples showed only a nematic LC phase over the
range from 2600 to 7300. The phase transitions of both types of polymers are discussed in relation to the molecular weight and MWD of the samples. The effect of the terminal group attached to the biphenyl group in the polymer is considered in relation to its possible steric effects. 相似文献
3.
A series of CuO–ZnO/Al 2O 3 solids were prepared by wet impregnation using Al(OH) 3 solid and zinc and copper nitrate solutions. The amounts of copper and zinc oxides were varied between 10.3 and 16.0 wt% CuO and between 0.83 and 7.71 wt% ZnO. The prepared solids were subjected to thermal treatment at 400–1000°C. The solid–solid interactions between the different constituents of the prepared solids were studied using XRD analysis of different calcined solids. The surface characteristics of various calcined adsorbents were investigated using nitrogen adsorption at −196°C and their catalytic activities were determined using CO-oxidation by O 2 at temperatures ranged between 125°C and 200°C. The results showed that CuO interacts with Al2O3 to produce copper aluminate at ≥600°C and the completion of this reaction requires heating at 1000°C. ZnO hinders the formation of CuAl2O4 at 600°C while stimulates its production at 800°C. The treatment of CuO/Al2O3 solids with different amounts of ZnO increases their specific surface area and total pore volume and hinders their sintering (the activation energy of sintering increases from 30 to 58 kJ mol−1 in presence of 7.71 wt% ZnO). This treatment resulted in a progressive decrease in the catalytic activities of the investigated solids but increased their catalytic durability. Zinc and copper oxides present did not modify the mechanism of the catalyzed reaction but changed the concentration of catalytically active constituents (surface CuO crystallites) without changing their energetic nature. 相似文献
4.
Novel Ir-substituted hexaaluminate catalysts were developed for the first time and used for catalytic decomposition of high concentration of N 2O. The catalysts were prepared by one-pot precipitation and characterized by X-ray diffraction (XRD), N 2-adsorption, scanning electronic microscopy (SEM) and temperature-programmed reduction (H 2-TPR). The XRD results showed that only a limited amount of iridium was incorporated into the hexaaluminate lattice by substituting Al 3+ to form BaIr xFe 1−xAl 11O 19 after being calcined at 1200 °C, while the other part of iridium existed as IrO 2 phase. The activity tests for high concentration (30%, v/v) of N 2O decomposition demonstrated that the BaIr xFe 1−xAl 11O 19 hexaaluminates exhibited much higher activities and stabilities than the Ir/Al 2O 3-1200, and the pre-reduction with H 2 was essential for activating the catalysts. By comparing BaIr xFe 1−xAl 11O 19 with BaIr xAl 12−xO 19 ( x = 0–0.8), it was found that iridium was the active component in the N 2O decomposition and the framework iridium was more active than the large IrO 2 particles. On the other hand, Fe facilitated the formation of hexaaluminate as well as the incorporation of iridium into the framework. 相似文献
5.
Two types of new chiral methacrylates, cinchoninyl(2-methacryloyloxyethyl)carbamate (CIMOC) and cinchonidinyl(2-methacryloyloxy-ethyl)carbamate (CDMOC) were synthesized from 2-methacryloyloxyethyl isocyanate (MOI) and cinchona alkaloid such as cinchonine and cinchonidine, respectively. Radical polymerizations of CIMOC and CDMOC were performed under several conditions to obtain the corresponding polymers whose specific optical rotations ([ ] 43525) were 84.0–89.0° and 0.39–0.72°, respectively. From the results of radical copolymerizations of RMOC (CIMOC and CDMOC, M1) with styrene (ST, M2) or methyl methacrylate (MMA, M2), monomer reactivity ratios ( r1, r2) and Alfrey–Price Q– e were determined: r1=0.18, r2=0.48, Q1=0.53, e1=0.92 for the CIMOC–ST system; r1=0.53, r2=0.26, Q1=4.91, e1=1.80 for the CIMOC–MMA system r1=0.59, r2=0.47, Q1=0.86, e1=0.33 for the CDMOC–ST system; r1=0.28, r2=0.59, Q1=2.15, e1=1.74 for the CDMOC–MMA system. The chiroptical properties of the copolymers were strongly influenced by co-units. Poly(RMOC)-bonded-silica gel as chiral stationary phase (CSP) was prepared for high performance liquid chromatography (HPLC). The CSPs resolved some racemates such as mandelic acid and trans-2-dibenzyl-4,5-di( o-hydroxyphenyl)-1,3-dioxolane by HPLC. The chiral recognition ability of poly(RMOC) may be due to the interaction between some cinchona alkaloid units and the racemates and/or to secondary and higher-ordered structures of the polymer. 相似文献
6.
Ammonia adsorption on Brønsted acid sites of WO 3 cluster supported on metal oxide supports: SnO 2, ZrO 2, and TiO 2, is analyzed by PIO analysis. We employed (HO)(WO 3) 4(H) and (HO)(WO 3) 9(H) on (SnO 2) 12, (ZrO 2) 12, and (TiO 2) 12, respectively, as supported Brønsted acid models and examined two types of Brønsted acid sites, an edge type and a face type. We estimated ammonia adsorption strength by total overlap population (∑OP) of all PIOs between the Brønsted acid site and NH 3. The order of acidity (∑OP) of each model is as follows: edge type: SnO 2, 0.0096 > ZrO 2, 0.0048 > TiO 2, −0.0001 face type: ZrO 2, −0.0759 > TiO 2, −0.0761 > SnO 2, −0.0867. The edge type adsorption is far stronger than the face type one. This order in the edge type coincides with the experimental results. The reason of these results is explained by the difference of the influence of oxygen atoms sitting near the N atom of NH 3. 相似文献
7.
Layered Li[Ni (1−x)/3Mn (1−x)/3Co (1−x)/3Cr x]O 2 materials with x = 0, 0.01, 0.02, 0.03, 0.05 are prepared by a solid-state pyrolysis method. The oxide compounds were calcined with various Cr-doped contents, which result in greater difference in morphological (shape, particle size and specific surface area) and the electrochemical (first charge profile, reversible capacity and rate capability) differences. The Li[Ni (1−x)/3Mn (1−x)/3Co (1−x)/3Cr x]O 2 powders were characterized by means of X-ray diffraction (XRD), charge/discharge cycling, cyclic voltammetry, and SEM. XRD experiment revealed that the Li[Ni (1−x)/3Mn (1−x)/3Co (1−x)/3Cr x]O 2 ( x = 0, 0.01, 0.02, 0.03, 0.05) were crystallized to well layered -NaFeO 2 structure. The first specific discharge capacity and coulombic efficiency of the electrode of Cr-doped materials were higher than that of pristine material. When x = 0.02, the sample showed the highest first discharge capacity of 241.9 mAh g −1 at a current density of 30 mA g −1 in the voltage range 2.3–4.6 V, and the Cr-doped samples exhibited higher discharge capacity and better cycleability under medium and high current densities at room temperature. 相似文献
9.
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% CO 2, 22% H 2O, 37.3% H 2, 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[H 2O] 1.0[CO 2] −0.1[H 2] −0.5, kf is the forward rate constant, β = ([CO 2][H 2])/( Keq[CO][H 2O]) 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 CO 2 and H 2. 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 H 2 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
10.
Gold loaded on TiO 2 (Au/TiO 2) catalysts were prepared using Au(I)–thiosulfate complex (Au(S 2O 3) 23−) as the gold precursor for the first time. The samples were characterized by UV–vis diffuse reflectance spectra, X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic absorption flame emission spectroscopy (AAS), and X-ray photoelectron spectroscopy (XPS) methods. Using Au(S 2O 3) 23− as gold precursor, ultra-fine gold nanoparticles with a highly disperse state can be successfully formed on the surface of TiO 2. The diameter of Au nanoparticles increases from 1.8 to 3.0 nm with increasing the nominal Au loading from 1% to 8%. The photocatalytic activity of Au/TiO 2 catalysts was evaluated from the analysis of the photodegradation of methyl orange (MO). With the similar Au loading, the catalysts prepared with Au(S 2O 3) 23− precursor exhibit higher photocatalytic activity for methyl orange degradation when compared with the Au/TiO 2 catalysts prepared with the methods of deposition–precipitation (DP) and impregnation (IMP). The preparation method has decisive influences on the morphology, size and number of Au nanoparticles loaded on the surface of TiO 2 and further affects the photocatalytic activity of the obtained catalysts. 相似文献
11.
The polymerization of racemic propylene oxide was performed using a chiral initiator obtained from the reaction of diethylzinc with (?) 3,3-dimethyl-1,2-butanediol. With this initiator R(+) enantiomer is preferentially incorporated into the polymer with a stereoelectivity ratio r equal to 1.8, the r value remaining constant during the polymerization. The polymer was fractionated into a crystalline isotactic part and an amorphous heterotactic part, both optically active. Partial stereoelectivities were determined for both fractions and found to be equal to 2.6 and 1.6 respectively for polymerization at 80°C. Two types of sites, stereospecific and non-stereospecific, formed in the first reaction between monomer and initiator are both active for the stereoelective polymerization. The stereospecificity of the monomer-initiator system increased at low temperatures, but the overall stereoelectivity remained constant and seemed to be an intrinsic property of the system. 相似文献
12.
Nanoparticles of Ce xZr 1−xO 2 ( x = 0.75, 0.62) were prepared by the oxidation-coprecipitation method using H 2O 2 as an oxidant, and characterized by N 2 adsorption, XRD and H 2-TPR. Ce xZr 1−xO 2 prepared had single fluorite cubic structure, good thermal stability and reduction property. With the increasing of Ce/Zr ratio, the surface area of Ce xZr 1−xO 2 increased, but thermal stability of Ce xZr 1−xO 2 decreased. The surface area of Ce 0.62Zr 0.38O 2 was 41.2 m 2/g after calcination in air at 900 °C for 6 h. TPR results showed the formation of solid solution promoted the reduction of CeO 2, and the reduction properties of Ce xZr 1−xO 2 were enhanced by the cycle of TPR-reoxidation. The Pd-only three-way catalysts (TWC) were prepared by the impregnation method, in which Ce 0.75Zr 0.25O 2 was used as the active washcoat and Pd loading was 0.7 g/L. In the test of Air/Fuel, the conversion of C 3H 8 was close to 100% and NO was completely converted at λ < 1.025. The high conversion of C 3H 8 was induced by the steam reform and dissociation adsorption reaction of C 3H 8. Pd-only catalyst using Ce 0.75Zr 0.25O 2 as active washcoat showed high light off activity, the reaction temperatures ( T50) of 50% conversion of CO, C 3H 8 and NO were 180, 200 and 205 °C, respectively. However, the conversions of C 3H 8 and NO showed oscillation with continuously increasing the reaction temperature. The presence of La 2O 3 in washcoat decreased the light off activity and suppressed the oscillation of C 3H 8 and NO conversion. After being aged at 900 °C for 4 h, the operation windows of catalysts shifted slightly to rich burn. The presence of La 2O 3 in active washcoat can enhance the thermal stability of catalyst significantly. 相似文献
13.
The effect of oxygen concentration on the pulse and steady-state selective catalytic reduction (SCR) of NO with C 3H 6 over CuO/γ-Al 2O 3 has been studied by infrared spectroscopy (IR) coupled with mass spectroscopy studies. IR studies revealed that the pulse SCR occurred via (i) the oxidation of Cu 0/Cu + to Cu 2+ by NO and O 2, (ii) the co-adsorption of NO/NO 2/O 2 to produce Cu 2+(NO 3−) 2, and (iii) the reaction of Cu 2+(NO 3−) 2 with C 3H 6 to produce N 2, CO 2, and H 2O. Increasing the O 2/NO ratio from 25.0 to 83.4 promotes the formation of NO 2 from gas phase oxidation of NO, resulting in a reactant mixture of NO/NO 2/O 2. This reactant mixture allows the formation of Cu 2+(NO 3−) 2 and its reaction with the C 3H 6 to occur at a higher rate with a higher selectivity toward N 2 than the low O 2/NO flow. Both the high and low O 2/NO steady-state SCR reactions follow the same pathway, proceeding via adsorbed C 3H 7---NO 2, C 3H 7---ONO, CH 3COO −, Cu 0---CN, and Cu +---NCO intermediates toward N 2, CO 2, and H 2O products. High O 2 concentration in the high O 2/NO SCR accelerates both the formation and destruction of adsorbates, resulting in their intensities similar to the low O 2/NO SCR at 523–698 K. High O 2 concentration in the reactant mixture resulted in a higher rate of destruction of the intermediates than low O 2 concentration at temperatures above 723 K. 相似文献
14.
Rate data have been obtained for CO hydrogenation on a well-characterized 11.7% Co/TiO 2 catalyst in a differential fixed bed reactor at 20 atm, 180–240°C, and 5% conversion over a range of reactant partial pressures. The resulting kinetic parameters can be used to model precisely and accurately the kinetics of this reaction within this range of conditions. Turnover frequencies and rate constants determined from this study are in very good to excellent agreement with those obtained in previous studies of other cobalt catalysts, when the data are normalized to the same conditions of temperature and partial pressures of the reactants. Based on this comparison CO conversion and the partial pressure of product water apparently have little effect on specific rate per catalytic site. The data of this study are fitted fairly well by a simple power law expression of the form − rCO= kPH20.74PCO−0.24, where k=5.1×10 −3 s −1 at 200°C, P=10 atm, and H 2/CO=2/1; however, they are best fitted by a simple Langmuir–Hinshelwood (LH) rate form − rCO= aPH20.74PCO/(1+ bPCO) 2 similar to that proposed by Yates and Satterfield. 相似文献
15.
A single-step complex decomposition method for the synthesis of bulk and alumina-supported γ-Mo 2N catalysts is described. The complex precursor (HMT) 2(NH 4) 4Mo 7O 24·2H 2O (HMT: hexamethylenetetramine) is converted to γ-Mo 2N under a flow of Ar in a temperature range of 823–1023 K. Furthermore, decomposition of the precursor in a NH 3 flow forms γ-Mo 2N in a temperature range of 723–923 K. Compared with direct decomposition of the precursor in Ar, the reaction in NH 3 shows obvious advantages that the nitride forms at a lower temperature. In addition, alumina-supported γ-Mo 2N catalysts with different nitride loadings can be prepared from the alumina-supported complex precursor in the Ar or NH 3 flow. The resultant catalysts exhibit good dibenzothiophene HDS activities, which are similar to the γ-Mo 2N/γ-Al 2O 3 prepared by traditional TPR method. The catalyst prepared by decomposition in an Ar flow exhibits highest activity. It proves that such a single-step complex decomposition method possesses the potential to be a general route for the preparation of molybdenum nitride catalysts. 相似文献
16.
The phase diagram of the Al 2O 3–ZrO 2–Nd 2O 3 system was constructed in the temperature range 1250–2800 °C. The liquidus surface of the phase diagram reflects the preferentially eutectic interaction in the system. Two new ternary and one new binary eutectics were found. The minimum melting temperature is 1675 °C and it corresponds to the ternary eutectic Nd 2O 3·11Al 2O 3 + F-ZrO 2 + NdAlO 3. The solidus surface projection and the schematic of the alloy crystallization path confirm the preferentially congruent character of phase interaction in the ternary system. The polythermal sections present the complete phase diagram of the Al 2O 3–ZrO 2–Nd 2O 3 system. No ternary compounds or regions of remarkable solid solution were found in the components or binaries in this ternary system. 相似文献
17.
The kinetics of the selective catalytic reduction (SCR) of NO by NH 3 in the presence of O 2 has been studied on a 5.5% Cu-faujasite (Cu-FAU) catalyst. Cu-FAU was composed of cationic and oxocationic Cu species. The SCR was studied in a gas phase-flowing reactor operating at atmospheric pressure. The reaction conditions explored were: 458< TR<513 K, 250 3 (ppm) < 4000, 12 (%) < 4. The kinetic orders were 0.8–1 with respect to NO, 0.5–1 with respect to O2, and essentially 0 with respect to NH3. Based on these kinetic partial orders of reactions and elementary chemistry, a wide variety of mechanisms were explored, and different rate laws were derived. The best fit between the measured and calculated rates for the SCR of NO by NH3 was obtained with a rate law derived from a redox Mars and van Krevelen mechanism. The catalytic cycle is described by a sequence of three reactions: (i) CuI is oxidized by O2 to “CuII-oxo”, (ii) “CuII-oxo” reacts with NO to yield “CuII-NxOy”, and (iii) finally “CuII-NxOy” is reduced by NH3 to give N2, H2O, and the regeneration of CuI (closing of the catalytic cycle). The rate constants of the three steps have been determined at 458, 483, and 513 K. It is shown that CuI or “CuII-oxo” species constitute the rate-determining active center. 相似文献
18.
Layered -titanate materials, Na xM x/2Ti 1−x/2O 2 (M=Co, Ni and Fe, x=0.2–0.4), were synthesized by flux reactions, and electrical properties of polycrystalline products were measured at 300–800 °C. After sintering at 1250 °C in Ar, all products show n-type thermoelectric behavior. The values of both d.c. conductivity and Seebeck coefficient of polycrystalline Na 0.4Ni 0.2Ti 0.8O 2 were ca. 7×10 3 S/m and ca. −193 μV/K around 700 °C, respectively. The measured thermal conductivity of layered -titanate materials has lower value than conductive oxide materials. It was ca. 1.5 Wm −1 K −1 at 800 °C. The estimated thermoelectric figure-of-merit, Z, of Na 0.4Ni 0.2Ti 0.8O 2 and Na 0.4Co 0.2Ti 0.8O 2 was about 1.9×10 −4 and 1.2×10 −4 K −1 around 700 °C, respectively. 相似文献
19.
A new class of polymer electrolytes, based on the interpenetrating polymer network approach, was obtained starting from functionalised macromers, of poly-ether nature, in the presence of a lithium salt (LiBF 4, LiClO 4, LiCF 3SO 3) and propylene carbonate (PC) or tetraethyleneglycol dimethylether (TGME), as plasticizers. The macromers were synthesised by living polymerisation employing a HI/I2 system as the initiator. The macromer has a polymerisable end group, which can undergo radical polymerisation, attached to a monodisperse poly-vinylether, containing suitable ethylene oxide groups for ion coordination. Monomers and macromers were characterised by FTi.r., u.v.–vis, 1H- and 13C-n.m.r. Self-consistent and easily handled membranes were obtained as thin films by a dry procedure using u.v. radiation to polymerise and crosslink the network precursors, directly on suitable substrates, in the presence of the plasticizer and the lithium salt. The electrolytic membranes were studied by complex impedance and their thermal properties determined by differential scanning calorimetry analysis. Ionic conductivities (σ) were measured for PC and TGME-based membranes at various plasticizer and salt contents as a function of T (60 to −20°C). LiClO4/PC/PE electrolytes, with 3.8% (w/w) salt and 63% PC, have the highest σ (1.15×10−3 and 3.54×10−4 S cm−1 at 20°C and −20°C, respectively). One order of magnitude lower conductivities are achieved with TGME; samples with 6% (w/w) LiClO4 and 45% (w/w) TGME exhibit σ values of 2.7×10−4 and 2.45×10−5 S cm−1 at 20°C and −20°C. 相似文献
20.
Selective catalytic reduction (SCR) activity for NO conversion to N 2 over γ-alumina, vanadia/alumina and molybdena/alumina catalysts has been investigated with methanol (MeOH) and dimethyl ether (DME) as reductants under lean conditions. Molybdena/alumina catalysts showed high efficiency for NO reduction with either reductant, especially at low temperature, which may involve surface formyl produced by oxidative dehydrogenation. Sulphated γ-alumina remains active for NO reduction with MeOH, while sulphated 5 wt.% MoO 3/Al 2O 3 remains active with both MeOH and DME over a broad temperature range. 相似文献
|