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1.
The H 2-TPR (temperature-programmed reduction) study was performed for supported copper oxide catalysts with low loading (0.5 wt% as copper). Among the various kinds of support materials (γ-Al 2O 3, TiO 2, ZrO 2, SiO 2, ZSM-5), alumina-supported copper oxide indicated a one-electron reduction behavior of Cu 2+ into Cu + ions in the presence of H 2. The reduction of the isolated Cu 2+ species in a tetragonally distorted octahedral symmetry into the low coordinated Cu + ions was identified by means of X-ray absorption spectroscopy (XANES and EXAFS). The isolated Cu + ions hosted by γ-Al 2O 3 surface were prevented from further reduction into metallic Cu 0 state under reducing condition with H 2 at 773 K. Less dispersed supported copper oxide species were easily reduced to Cu 0 metal particles with H 2 at 573 K regardless of the kinds of support materials. It is suggested that the one-electron redox behavior of the isolated copper oxide species over γ-Al 2O 3 promotes the catalytic reduction of NO with CO in the presence of oxygen on the basis of redox-type mechanism between Cu 2+ and Cu + in atomically dispersed state. 相似文献
2.
采用共沉淀法和沉淀浸渍法制备了纳米氧化铈-二氧化硅(CeO 2-SiO 2)介孔材料吸附剂,主要考察了其对水中铜离子(Cu 2+)的吸附行为。通过X射线衍射(XRD)、扫描电镜(SEM)和氮吸附(BET)等手段对合成的介孔材料进行了性能表征,并通过静态吸附实验分析了溶液pH、溶液初始金属离子质量浓度、吸附剂用量、吸附时间等条件对介孔材料吸附Cu 2+性能的影响。结果表明:共沉淀法制备的纳米CeO 2-SiO 2介孔材料对Cu 2+的去除效果较沉淀浸渍法要好;当溶液pH=7.0时CeO 2-SiO 2介孔材料对Cu 2+的吸附效果最好,20 min时基本达到吸附平衡;溶液初始Cu 2+浓度增大Cu 2+去除率降低,Cu 2+累计吸附量增大;随着吸附剂用量增加Cu 2+去除率增大,当CeO 2-SiO 2吸附剂用量为0.15 g/L时对Cu 2+的去除率趋于稳定;CeO 2-SiO 2吸附剂对不同金属离子吸附性能由大到小的顺序为Cu 2+、Fe 2+、Mn 2+,该吸附过程均符合准二级动力学模型。 相似文献
3.
The catalytic decomposition of acrylonitrile (AN) over Cu-ZSM-5 prepared with various Cu loadings was investigated. AN conversion, during which the nitrogen atoms in AN were mainly converted to N 2, increased as Cu loading increased. N 2 selectivities as high as 90–95% were attained. X-ray diffraction measurements (XRD) and temperature-programmed reduction by H 2 (H 2-TPR) showed the existence of bulk CuO in Cu-ZSM-5 with a Cu loading of 6.4 wt% and the existence of highly dispersed CuO in Cu-ZSM-5 with a Cu loading of 3.3 wt%. Electron spin resonance measurements revealed that Cu-ZSM-5 contains three forms of isolated Cu 2+ ions (square-planar, square-pyramidal, and distorted square-pyramidal). The H 2-TPR results suggested that in Cu-ZSM-5 with a Cu loading of 2.9 wt% and below, Cu + existed even after oxidizing pretreatment. The activity of AN decomposition over Cu/SiO 2 suggested that CuO could form N 2, but, independent of the CuO dispersion, nitrogen oxides (NO x) were formed above 350 °C. Cu + and the square-pyramidal and distorted square-pyramidal forms of Cu 2+ showed low activity for AN decomposition. Temperature-programmed desorption of NH 3 suggested that N 2 formation from NH 3 proceeded on Cu 2+, resulting in the formation of Cu +. The Cu + ions were oxidized to Cu 2+ at around 300 °C. Thus, high N 2 selectivity over Cu-ZSM-5 with a wide range of temperature was probably attained by the reaction over the square-planar Cu 2+, which can be reversibly reduced and oxidized. 相似文献
4.
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
5.
Cu 2+ ion-exchanged pillared clays are substantially more active than Cu 2+-ZSM-5 for selective catalytic reduction (SCR) of NO by hydrocarbons. More importantly, H 2O (or SO 2) has only mild effects on their activities. First results on Cu 2+-exchanged TiO 2-pillared montmorillonite were reported by this laboratory (Yang and Li, Ref. [1]), that showed overall activities two to four times higher than Cu 2+-ZSM-5. A delaminated pillared clay was subjected to Cu2+ ion-exchange and studied for SCR by C2H4 in this work. The Cu2+ ion-exchanged delaminated Al2O3-pillared clay yielded substantially higher SCR rates than both Cu2+-exchanged TiO2-pillared clay and Cu2+-ZSM-5 at temperatures above 400°C. The peak NO conversion was 90% at 550°C and at a space velocity of 15,000 h−1 (with O2 = 2%). The peak temperature decreased as the concentration of O2 was increased. The macroporosity in the delaminated pillared clay was partially responsible for its higher peak temperatures (than that for laminated pillared clays). At 1000 ppm each for NO and C2H4, the NO conversion peaked at 2% O2 for all temperatures. H2O and SO2 caused only mild deactivation, likely due to competitive adsorption (of SO2 on Cu2+ sites and H2O on acid sites). The high activity of Cu2+-exchanged Al2O3-pillared clay was due to a unique combination of the redox property of the Cu2+ sites and the strong Lewis acidity of the pillared clay. The suggested mechanism involved NO chemisorption (in the presence of O2) on Cu2+OAl3+-on the pillars, and C2H4 activation on the Lewis acid sites to form an oxygenated species. 相似文献
6.
采用简单的一步电沉积方法制备了Cu 2+掺杂的MnO 2材料。通过XRD、SEM、TEM等方法对材料进行了表征,结果表明其具有蓬松多孔的纳米结构,作为电池正极材料时有利于Zn 2+的存储,具有较高的电池容量。与未掺杂样品相比Cu 2+掺杂的MnO 2材料有更好的电化学性能,在电流密度为200 mA/g时,比容量达到235 mAh/g,增加了47.8%,阻抗也由997.3 Ω降到了564.3 Ω。 相似文献
7.
近年来,钙钛矿因其特殊的结构受到广泛的关注。其中,全无机钙钛矿量子点作为下一代发光材料更因其优异的发光性能得到了广泛的研究和关注。但是因为其本身的铅(Pb)元素带来的毒性和较差的稳定性,钙钛矿量子点在生产和应用方面依然面临着诸多阻碍。为了解决这些难题,介绍了一种铜离子(Cu 2+)B位掺杂CsPbCl 3钙钛矿量子点。采用了热注射的方法成功地将Cu 2+引入CsPbCl 3钙钛矿量子点中。研究发现,Cu 2+掺杂CsPbCl 3量子点能够保持初始四方晶体结构。由于Cu 2+的掺杂,有效地消除了CsPbCl 3量子点的表面缺陷,从而通过辐射途径促进了激子复合,提高了CsPbCl 3量子点的发光性质。通过稳定性对比测试发现,一段时间内,Cu 2+掺杂CsPbCl 3量子点在水中的发光强度明显高于CsPbCl 3量子点。 相似文献
8.
ZSM-5 zeolites modified with Cu + ions were prepared either by the high-temperature chemical reaction of hydrogen form with CuCl vapour or by the wet ion exchange with subsequent reduction of the modified samples in CO at 873 K. Adsorption of H 2, N 2 or C 2H 6 by Cu + ions was studied by DRIFTS and by volumetric technique. The conclusions about the structure of adsorption complexes were supported by the DFT cluster quantum chemical calculations. The obtained results indicated that in addition to the previously reported strong adsorption of nitrogen, the univalent copper also unusually strongly adsorbs molecular hydrogen and ethane. Adsorption of hydrogen is the most amazing since the observed low-frequency shifts of the HH stretching vibrations were as high as about 1000 cm −1. This is quite different from much weaker H 2 perturbation by Cu 2+ cations. Adsorption of ethane by Cu + ions also resulted in the low-frequency shifts of some of CH IR stretching bands up to 400 cm −1. The DFT cluster modelling indicated that both adsorption of hydrogen and ethane could be explained by interaction with the isolated Cu + ions localized at the sites of the ZSM-5 framework. Quantum chemical calculations indicated the important role in the bonding of adsorbed hydrogen and ethane of electron back donation from d π-orbitals of Cu + ions to the σ *HH or CH orbitals. The overall yield of Cu + sites of the strong H 2 or N 2 adsorption is about twice lower than the total copper content. 相似文献
9.
通过对b-环糊精(b-CD)改性制备了阴离子b-环糊精/Fe 3O 4磁性微球(b-CDM),并研究了b-CDM对Cu 2+吸附的热力学、动力学及循环使用性能,借助数学拟合的方法得到了吸附热力学和动力学参数,探讨其吸附机理。研究表明,b-CDM对Cu 2+的吸附是一个自发的放热过程,Langmuir与Freundlich等温吸附模型均适用于b-CDM对Cu 2+的吸附研究,b-CDM对Cu 2+的吸附经历颗粒外部扩散-孔隙扩散-吸附反应3个阶段,该吸附过程既存在物理吸附,又有化学吸附,在吸附温度298、308、318 K下得到的吸附速率常数分别为0.0906、0.1161、0.1674 g·mmol -1·min -1,吸附表观活化能为24.12 kJ·mol -1,且随着介质中Cu 2+平衡吸附量的增大,b-CDM对Cu 2+的吸附驱动力由焓变转变为熵变。b-CDM重复利用8次后,对Cu 2+的除去率由首次使用时的95.20%下降至88.21%。 相似文献
10.
Single crystals of Lithium Ammonium Sulphate doped with Cu 2+ ions were grown by slow evaporation technique. Electronic absorption spectra have been recorded at room and liquid nitrogen temperatures on Cary-2390 spectrophotometer. The spectrum is characteristic of a Cu 2+ ion in octahedral symmetry. From the magnitude and and relative position of the bands a successful interpretation of all the observed bands has been made. The crystal field and tetragonal field parameters are derived. The observed and calculated energies are in good agreement. 相似文献
11.
Among various Cu/ZnO/ZrO 2 catalysts with the Cu/Zn ratio of 3/7, the one with 15 wt.% of ZrO 2 obtains the best activity for methanol synthesis by hydrogenation of CO. The TPR, TPO and XPS analyses reveal that a new copper oxide phase is formed in the calcined Cu/ZnO/ZrO 2 catalysts by the dissolution of zirconium ions in copper oxide. In addition, the Cu/ZnO/ZrO 2 catalyst with 15 wt.% of ZrO 2 turns out to contain the largest amount of the new copper oxide phase. When the Cu/ZnO/ZrO 2 catalysts is reduced, the Cu 2+ species present in the ZrO 2 lattice is transformed to Cu + species. This leads to the speculation that the addition of ZrO 2 to Cu/ZnO catalysts gives rise to the formation of Cu + species, which is related to the methanol synthesis activity of Cu/ZnO/ZrO 2 catalyst in addition to Cu metal particles. Consequently, the ratio of Cu +/Cu 0 is an important factor for the specific activity of Cu/ZnO/ZrO 2 catalyst for methanol synthesis. 相似文献
12.
This paper deals with the redox properties of Cu ions implanted in ZSM-5 and supported on Al 2O 3, catalysts active in the selective reduction of NO by hydrocarbons such as propane. Data on the reducibility of the Cu systems in various atmospheres (vacuum, CO, H 2, O 2) and on their DeNO x activity are presented. The methods used to obtain informations on the surface and bulk transformations (and their link with catalytic behaviour) are complementary: UV–visible diffuse reflectance spectroscopy being useful to detect the presence of Cu 2+ and Cu 0, while Cu + is detected indirectly by the analysis of the IR spectrum of CO bound selectively to this cation. The main contributions to the previous knowledge are the following: it is possible to distinguish CO bound to isolated and non-isolated Cu+ ions; the isolated Cu2+ ions are reducible under vacuum without participation of organic impurities; the more active solids for the NO reduction into N2 are characterized by the presence of isolated Cun+ ions beside the additional influence of the zeolitic framework; after the formation of Cu+ ions the redox cycles are reversible but, after the formation of Cu0, the reversibility or irreversibility of the redox cycles and the restoration of the SCR activity are function of the copper content; the activity decreases after agglomeration into bulk oxides; there is no formation of bulk CuO during the reaction and, with reducing and moderate oxidizing mixtures, part of the copper remains as cuprous ions. 相似文献
13.
为了考察羧甲基纤维素钠(CMC)对重金属离子 的螯合能力,利用紫外分光光度法测定了不同c(Cu 2+)/c(-COO -)浓度比下CMC与 形成螯合物的吸收光谱,探讨了螯合物的组成,并计算其稳定常数。结果表明:CMC对 有螯合作用,当c(Cu 2+)/c(-COO -)小于0.6,螯合物在237 nm处出现最大吸收峰,-COO -为主要配体,与 按物质的量比为2:1进行螯合,此时,螯合物稳定常数为1.88×10 10;c(Cu 2+)/c(-COO -)为0.6~1.0时,214、237 nm处出现最大吸收峰,-COO -、-OH都参与螯合反应并形成新的螯合物;c(Cu 2+)/ c(-COO -)大于1.0时,214 nm存在最大吸收峰,-OH为主要配体。考察了利用CMC螯合去除溶液中 的效果,实验表明,CMC-Cu螯合物可在溶液中直接析出,析出物为絮状沉淀。当c(Cu 2+)/c(-COO -)等于0.5时为最佳CMC用量,此时上清液中 去除率可以达到96%以上。 相似文献
14.
Electrochemical technologies for the on-site treatment of spent acid etchant have received great attention due their ease of operation and economic benefits. On the other hand, a large amount of Cl 2 is generated during the electrolysis process, which leads to potential environmental risks. In the present work, a novel threecompartment ceramic membrane flow reactor, including a cathode chamber, an anode chamber, and a gas absorption chamber was developed. The three chambers were divided by an Al 2O 3 ceramic membrane and a breathable hydrophobic anode diffusion electrode (ADE). The Cl 2 evolution onset potential of the ADE was increased to 1.19 V from 1.05 V of the graphite felt, effectively inhibiting the chlorine evolution reaction (CER). The anode-generated Cl 2 diffused into the gas absorption chamber through the ADE and was eventually consumed by the H 2O 2 adsorbent. Cu could be recovered without emitting chlorine due to the special structure of reactor. The current efficiency of copper precipitation and cathode reduction from Cu 2+ to Cu + reached 97.7% at a working current of 150 mA. These results indicated that the novel membrane reactor had high potential for application in the copper recovery industry. 相似文献
15.
Methyl methacrylate was polymerized in aqueous medium initiated by a copper(II)-ascorbic acidoxygen system at 40°C and a kinetic study of the reaction is presented. The rate of polymerization, Rp showed an increase, constancy and then a decrease with increase in the [Cu 2+]. The order with respect to [Cu 2+] was 0.5 in the rate increase region. The order in monomer concentration changed gradually from 1.0 to 2.0 with increase in [Cu 2+]. Rp became independent of ascorbic acid (AA) concentration and oxygen concentration at high concentrations. These results indicate that termination by mutual interaction of chain radicals predominates at low [Cu 2+] while termination was exclusively by metal ions at high [Cu 2+]. Rp was also observed to increase with temperature and ionic strength and to Kp/ Kt1/2 value was calculated and compared with literature values. Chain lengths were determined by viscometry for the polymers obtained under various experimental conditions. 相似文献
16.
The adsorption of N 2 on a copper ion-exchanged ZSM-5 sample (CuZSM-5) prepared by ion exchange using an aqueous solution of copper propionate, Cu(C 2H 5COO) 2, was examined at room temperature by measuring the FT-IR spectra, adsorption isotherms and heat of adsorption. This sample was found to be extremely efficient in terms of N 2 adsorption with regard to both the amount and the energy (i.e., heat) of adsorption, compared with samples prepared by a conventional ion-exchange method using an aqueous solution involving Cu 2+ and simple counter ions, Cl − or NO 3−. To clarify the specificity of the newly-prepared sample, the ion-exchange of ZSM-5 with Cu 2+ was carried out by employing aqueous solutions involving Cu 2+ and various types of counter ions [propionate (C 2H 5COO −), acetate (CH 3COO −), formate (HCOO −), chloride (Cl −) and nitrate (NO 3−) ions]. When the ion exchange was performed by using a Cu(C 2H 5COO) 2 or Cu(CH 3COO) 2 solution, the Cu 2+ species with propionate or acetate ligand (in the monomer state) were ion-exchanged in ZSM-5, as confirmed by the DR, EPR and FT-IR spectra for CuZSM-5. In contrast, Cu 2+ species were present in the form of aquo-complexes in samples prepared with other solutions. This distinct difference can be ascribed to the difference in the p Ka values of the counter ions; carboxylate ions, with a high p Ka value, are inclined to form a complex with Cu 2+. Using this newly applied Cu(C 2H 5COO) 2 solution, the present ion-exchange method has the potential to develop new effective materials that possess the specific adsorption and catalytic properties of CuZSM-5. 相似文献
17.
The redox behavior and states of Cu ions in Cu ion-exchanged MFI (Cu( n)-MFI, n: exchange level) have been investigated by means of temperature-programmed desorption (TPD) of oxygen, diffuse reflectance (DR) UV–VIS spectroscopy and Cu + photoluminescence (PL) spectroscopy. TPD chromatograms of oxygen from Cu(n)-MFI were characterized by the appearance of three desorption peaks: (below 200°C), β (300–500°C) and γ (above 500°C). It has been suggested that and β oxygen are extra-lattice oxygen adsorbed on Cu ions, while γ oxygen is lattice oxygen coordinated to Cu ions. The Cu + emission was tremendously reduced once the catalyst contacted with O 2 and NO at elevated temperatures such as 500°C, and it was almost invisible under the working state of the catalyst, suggesting that PL-active Cu + ions are not real active sites under the working state. The desorption of β oxygen was intimately related to the creation of active centers for the NO decomposition reaction. DR measurements showed that the desorption of β oxygen caused tetragonal Cu 2+ to decrease and trigonal Cu 2+ to increase simultaneously. It has been proposed that both Cu 2+ and Cu + are involved in the NO decomposition catalysis over Cu-MFI under the working state. 相似文献
18.
Copper ion-exchanged zeolites ZSM5 with SiO 2:Al 2O 3 molar ratios 33 and 53 have been subjected to activity tests for direct decomposition of NO (2000 ppm, GHSV 560–5400 h −1). In situ infrared measurements were used to follow the reaction and surface and gas phase compositions. IR studies were also done in excess oxygen with rapid NO 2 formation in the gas phase. A high level of overexchange of copper in the zeolite in combination with a low concentration of acid sites, concurrent with a high SiO2:Al2O3 ratio, enhances the conversion of NO. A vibrational band at 1631 cm−1 is observed below the light-off temperature and interpreted as a bridged nitrato group bound to Cu2+–O–Cu2+ dimers. This band disappears above the light-off temperature but the intensity below this temperature correlates with the catalytic activity. We interpret that these bridge bound nitrato groups act as siteblockers on the active sites for NO conversion and that a tentative reaction intermediate, N2O3, also binds in a bridge configuration to the same Cu2+–O–Cu2+ dimers. A second nitrato group with unidentate coordination and vibrational bands at 1598/1575 cm−1 probes isolated copper ions. A third infrared band at 2130 cm−1 confirms previous observations of
-ions bound to the zeolite. We conclude that these species are coordinated to deprotonated and negatively charged sites on the zeolite and that these sites for
adsorption are blocked by Cu2+ ion-exchange. The 2130 cm−1 species appear to have no role in direct NO decomposition but the adsorption sites are crucial for the stability of the zeolite and intimately related to ion mobility in the lattice. Prolonged immersion of the zeolite in dilute solutions of copper ions improves the catalyst performance by copper hydroxylation leading to enhanced formation of the above dimers. A high SiO2:Al2O3 ratio leads to more stable catalysts, particularly in combination with a modest overexchange of copper ions. Excessive amounts of copper escalates the deactivation of the Cu-ZSM5 catalyst through the migration and sintering of cupric oxide crystallites. 相似文献
19.
为探索阳离子对水热制备脱硫石膏晶须结晶调控的影响,本文以预处理后的脱硫石膏为原料,NaCl、Cu Cl 2、Al Cl 3为添加剂采用水热法制备脱硫石膏晶须,重点研究Cl -存在条件下阳离子对脱硫石膏晶须结晶的影响及其作用机理。结果表明,Na +、Cu 2+、Al 3+对脱硫石膏晶须的显微结构、长径比和品质均有一定的影响,其中Cu 2+影响最为显著。Cu 2+可在晶须的(200)、(400)和(020)晶面发生化学吸附形成Cu SO 4膜层,使其径向生长受阻;同时,少量Cu 2+可取代Ca 2+,促进Ca 2+的去溶剂化,使晶须长径比增大至200。Na +和Al 3+均通过物理吸附作用于脱硫石膏晶须(200)、(400)和(020)晶面而阻碍其径向生长。此外,Al 3+与溶液中的OH 相似文献
20.
TM/TiO 2/SiO 2 photocatalysts were prepared by the photodeposition method using transition metal salts (TM=Fe 3+, Co 2+, Ni 2+ and Cu 2+) as precursors and the surface bond-conjugated TiO 2/SiO 2 as supporter in N 2 atmosphere, and were characterized by XRD, XPS, UV-Vis diffuse reflection and zeta-potential. Their photocatalytic activities were evaluated using reactive brilliant red K-2G (K-2G) and cationic blue X-GRL (CBX) showing different adsorption behavior on the oxides. Fe, Cu supported TiO 2/SiO 2 can efficiently extend the light absorption to the visible region. XPS analysis verified that the introduction of transition metal lead to the changes of the electronic environmental of Ti cations and the zeta-potential of oxides. As a result, K-2G has higher adsorption on the modified TiO 2/SiO 2 than that on the baked one, while the adsorption of CBX has a little change on the both oxides. At the same time, for the photodegradation of K-2G, Fe 3+, Co 2+, Ni 2+-modified catalysts show that their photoactivities are 3.3–2.2 times higher than the bare one. On the contrast, all transition-metal-supported catalysts have no significant activity improvement except that Fe/TiO 2/SiO 2 shows 1.68 times higher activity for the photodegradation of CBX. The results indicate that the photoactivity could be increased in photodegradation of dyes by changing the performances of adsorption to dyes and absorption to light of photocatalyst. 相似文献
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