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1.
The effect of the amount of precipitant ammonia on the Cu0/Cu+ratio of Cu/Si O2 prepared by the deposition–precipitation method is investigated. Species at different preparation stages, resulted from the amount of ammonia used, are identified by the XRD and FTIR techniques. Chrysocolla together with either copper nitrate hydroxide or copper hydroxide coexist in the uncalcined catalysts. Upon calcination, the latter two species are converted to Cu O particles while chrysocolla remains. Following reduction, Cu O is transformed to metallic Cu and chrysocolla is converted to Cu2 O. The value of Cu0/Cu+ratio can be evaluated using the peak areas in their TPR profiles. Hydrogenation of dimethyl oxalate(DMO) to ethylene glycol(EG) shows that the selectivity of EG depends on the Cu0/Cu+ratio. Catalyst prepared with the addition of ammonia solution at n(NH3)/n(Cu2+) = 0.9 for precipitation–deposition gains a more suitable Cu0/Cu+ratio upon reduction and thus has a higher selectivity for EG.  相似文献   

2.
采用蒸氨法制备出不同Cu负载量的xCu/SiO_2-AE催化剂,并将其用于二甲醚水蒸气重整制氢反应。当Cu负载量为30%(w)时,30Cu/SiO_2-AE催化剂表现出最佳的催化性能。结果显示,该方法制备的催化剂表面具有高度分散的CuO和层状硅酸铜物相,经还原后分别形成Cu~0和Cu~+物种。与常规浸渍法制备的30Cu/SiO_2-IM催化剂相比,蒸氨法制备的30Cu/SiO_2-AE催化剂具有优异的催化稳定性和活性,这与其独特的层状结构和表面Cu~0与Cu~+之间的协同作用相关。  相似文献   

3.
采用蒸氨法制备的xGa-Cu/SiO_2催化剂可以同时产生Cu~0和Cu~+物种,加入Ga后催化剂的二甲醚水蒸气重整反应活性和选择性都有很大程度的提高,其中5Ga-Cu/SiO_2催化剂在380°C时的二甲醚转化率为99.8%,CO选择性为4.8%。通过透射电子显微镜(TEM),氢气-程序升温还原(H_2-TPR),N_2O滴定和X射线光电子能谱(XPS)结果发现,Ga与Cu物种之间的相互作用,一方面可以提高Cu物种的分散度,另一方面可以促进Cu~+的形成。通过改变Ga负载量可以调变Cu~+/(Cu~0+Cu~+)的比例,氢气的时空收率结果表明,Ga通过调变Cu~+/(Cu~0+Cu~+)影响催化活性,并且当Cu~+/(Cu~0+Cu~+)=0.5时,氢气时空收率达到最大值为5.02mol·g~(-1)·h~(-1)。程序升温表面反应(TPSR)结果表明,Ga通过促进水气变换反应提高反应产物CO_2选择性。  相似文献   

4.
采用尿素水解法制备了Cu/SiO2催化剂, 探究其用于乙酸甲酯(MA)加氢制取乙醇的催化性能, 并通过N2物理吸附、X射线衍射(XRD)、程序升温还原(TPR)、透射电子显微镜(TEM)和X射线光电子能谱(XPS)等表征方法分析了催化剂的物理化学特性, 探究了铜负载量和还原温度等对催化剂结构的影响, 以及与催化活性之间的关系. 发现在铜负载量分别为10%、20%和30% (质量分数, w)的催化剂中, 铜负载量为20%的催化剂因具有较多且分散均匀的活性组分而表现出最佳的加氢效果. 接着在铜负载量为20%的催化剂上研究了还原温度(270, 350, 450 ℃)对催化性能的影响, 发现在350 ℃下还原的催化剂活性最高, 在最佳的反应条件下, 乙酸甲酯转化率达到97.8%, 乙醇选择性达到64.9% (理论最大值为66.6%), 主要归属于它具有较高的铜物种分散度, 最合适的Cu0/(Cu0+Cu+)摩尔比例, 同时实现了解离氢气和活化乙酸甲酯的功能.  相似文献   

5.
Direct transformation of ethanol to ethyl acetate was investigated on a series of Cu(ZrO2)/SiO2 catalysts. Inductively coupled plasma(ICP), surface area analysis, X-ray diffraction(XRD), H2-temperature programmed reduction(H2-TPR), X-ray photoelectron spectroscopy(XPS), NH3-temperature programmed desorption(NH3-TPD) and Fourier transform-infrared spectroscopy(FTIR) techniques were used to characterize the catalysts. The results reveal that ZrO2 can improve the dispersion of copper species and increase the acidity of the Cu(ZrO2)/SiO2 catalysts. The Cu0 is responsible for ethanol dehydrogenation to acetaldehyde, and both the Lewis acid and Brønsted acid sites were in favor of the selectivity to ethyl acetate. The synergistic effect of Cu0 and an appropriate amount of acidic sites played an important role in the production of ethyl acetate.  相似文献   

6.
采用共沉淀法分别制备了不同F-T组分(Fe、Co、Ni)改性的KCuZrO_2催化剂,并用于催化CO加氢合成异丁醇。通过BET、XRD、TEM、XPS、H_2-TPR、CO-TPD以及in-situ DRIFTS对催化剂进行了表征。结果显示,F-T组分的加入促进了乙醇和丙醇的形成,但是对异丁醇选择性影响不同。结果表明,Fe促进了催化剂中各组分的分散,活性组分Cu在催化剂表面发生了富集,提高了H_2/CO活化吸附;另外,KFeCuZrO_2的催化剂表面含有较多的C_1物种,有利于乙醇和丙醇进一步发生β-加成反应得到异丁醇,而Co和Ni改性的催化剂上缺少足够的C_1物种,因此,异丁醇的选择性并未明显增加。Co的引入对催化剂结构以及Cu的分散影响不大,但是Co改性后催化剂性能有所下降,其原因是催化剂发生了失活;Ni添加后催化剂比表面积有所减小,且催化剂表面Cu/Zr物质的量比也降低到0.19,催化剂粒径增大,Cu-Zr之间相互作用减弱,异丁醇选择性降低。  相似文献   

7.
Micron-sized silica gel particles were chemically modified on their surfaces with the coupling agent, γ-methacryloxypropyl trimethoxysilane (MPS), double bond was introduced onto the surfaces of silica gel particles, and the modified particles MPS–SiO2 were obtained. Then, poly(4-vinylpyridine) (P4VP) was grafted from the silica gel surfaces, and grafting particles P4VP/SiO2 was prepared. Finally, the coordination between grafted P4VP and cupric ions Cu2+ was performed, and the supported complex Cu(II)–P4VP/SiO2 was obtained. The grafting particles P4VP/SiO2 and the supported complex Cu(II)–P4VP/SiO2 were characterized with infrared spectra (FTIR), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). Cu(II)–P4VP/SiO2 was used as a catalyst for the oxidation of ethyl benzene into acetophenone with molecular oxygen under ordinary pressure. The experimental results show that the supported complex Cu(II)–P4VP/SiO2 can be successfully prepared via grafting polymerization of 4VP and coordination between the grafted P4VP and cupric ions Cu2+. In oxidation of ethyl benzene into acetophenone by molecular oxygen under ordinary pressure, the supported complex Cu(II)–P4VP/SiO2 displayed high catalytic activity and excellent catalytic selectivity up to more than 98% for the transformation of ethyl benzene to acetophenone.  相似文献   

8.
Cu-ZnO is broadly used as a catalyst in CO2 reduction to produce methanol, but fabricating small-sized Cu-ZnO catalysts with strong Cu-ZnO interactions remains a challenge. In this work, a simple, low-cost method is proposed to synthesize small-sized Cu-ZnO/SiO2 with high activity and controllable Cu-ZnO interactions derived from copper silicate nanotubes. A series of Cu-ZnO/SiO2 samples with different amounts of ZnO were prepared. The activities of the as-prepared catalysts for methanol synthesis were tested, and the results revealed a volcano relationship with the weight fraction of ZnO. At 523 K, the methanol selectivity increased from 20% to 67% when 14% ZnO was added to the Cu/SiO2 catalyst, while the conversion of CO2 increased first and then decreased with the addition of ZnO. The optimum space time yield (STY) of 244 g·kg-1·h-1 was obtained on C-SiO2-7%ZnO at 543 K under 4.5 MPa H2/CO2. Furthermore, the synergistic effect of Cu and ZnO was studied by high resolution transmission electron microscopy (HRTEM), powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), in situ diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS), and temperature-programmed reduction (TPR) analyses. The HRTEM images showed that the Cu particles come in contact with ZnO more frequently with increased addition of ZnO, indicating that the catalysts with higher ZnO contents have a greater probability of formation of the Cu-ZnO interface, which promotes the catalytical activity of Cu-ZnO/SiO2. Meanwhile, the HRTEM images, XRD patterns, and TPR results showed that the addition of excess ZnO leads to an increase in the size of the Cu particles, which in turn decreases the total number of active sites and further degrades the activity of the catalysts. The activation energy (Ea) for methanol synthesis and reverse water gas shift (RWGS) was calculated based on the results of the catalytical test. With the addition of ZnO, Ea for methanol synthesis decreased from 72.5 to 34.8 kJ·mol-1, while that for RWGS increased from 61.3 to 102.7 kJ·mol-1, illustrating that ZnO promotes the synergistic effect of Cu-ZnO. The results of XPS and in situ DRIFTS showed that the amount of Cu+ species decreases with the addition of ZnO, indicating that the Cu-ZnO interface serves as the active site. The Cu surface area and the turnover frequency (TOF) of methanol were calculated based on the H2-TPR curves. The TOF of methanol on the Cu-ZnO/SiO2 catalysts at 543 K increased from 1.5 × 10-3 to 3.9 × 10-3 s-1 with the addition of ZnO, which further confirmed the promotion effect of the Cu-ZnO interface on the methanol synthesis. This study provides a method to construct Cu-ZnO interfaces based on copper silicate and to investigate the influence of ZnO on Cu-ZnO/SiO2 catalysts.  相似文献   

9.
Highly active and selective Cu/SiO2 catalysts for hydrogenation of dimethyl oxalate(DMO) to ethylene glycol(EG) were successfully prepared by means of a convenient one-pot synthetic method with tetraethoxysilane( TEOS) as the source of silica. XRD, H2-TPR, SEM, TEM, XRF and N2 physisorption measurements were performed to characterize the texture and structure of Cu/SiO2 catalysts with different copper loadings. The active components were highly dispersed on SiO2 supports. Furthermore, the coexistence of Cu0 and Cu+ contributed a lot to the excellent performance of Cu-TEOS catalysts. The DMO conversion reached 100% and the EG selectivity reached 95% at 498 K and 2 MPa with a high liquid hourly space velocity over the 27-Cu-TEOS catalyst with an actual copper loading of 19.0%(mass fraction).  相似文献   

10.
以NH4Y分子筛为载体、 乙酰丙酮铜为铜源, 采用固相反应法制备了无氯CuY催化剂, 并用于催化甲醇氧化羰基化合成碳酸二甲酯(DMC). 结合不同反应时间催化剂的X射线衍射(XRD)、 N2吸附-脱附、 热重(TG)、 程序升温脱附/还原(NH3-TPD/H2-TPR)、 透射电子显微镜(TEM)和X射线光电子能谱(XPS)等表征结果, 分析了反应过程中Cu物种演变对其催化活性的影响. 结果表明, 新鲜催化剂中铜物种主要以Cu+形式存在, 占铜物种的48%; 随着反应的进行, 活性中心Cu+逐渐被氧化为Cu2+, 进而生成CuO物种, 部分CuO逐渐迁移至催化剂外表面. 在反应100 h内, Cu+含量逐渐减小至36.7%, CuO含量增加, 导致DMC的时空收率及选择性不断下降, 副产物二甲氧基甲烷(DMM)和甲酸甲酯(MF)的选择性逐渐提高. 当反应时间延长至190 h时, Cu+含量为33.6%, 略有下降, DMC的时空收率和选择性趋于平稳. 继续延长反应时间至300 h, 催化剂中铜物种状态基本不变, 催化剂催化性能保持稳定.  相似文献   

11.
采用浸渍法制备了系列铜锰复合氧化物分子筛催化剂(Cu-Mn/SAPO-34),在固定床反应器上考察不同Cu/Mn质量比对分子筛催化剂选择催化还原NO的影响,利用XRD、NH_3-TPD、H_2-TPR、XPS等手段对催化剂进行了表征分析。结果表明,双金属改性的Cu-Mn/SAPO-34催化剂在NH_3-SCR反应中表现出较为优异的催化活性,具有较宽的活性温度窗口。当Cu/Mn质量比为1∶4时,催化剂具有最宽的活性温度窗口,NO_x转化率在250℃已达到85.39%,在300-400℃转化率均达到96%以上,450℃时仍能达到90%。铜和锰物种高度分散于催化剂表面,未改变SAPO-34的晶体结构,且构成协同作用。Cu-Mn共同负载促进了Cu~(2+)向Cu~+的转变,增加了高价态Mn~(4+)和Mn~(3+)的比例,有利于提高低温活性,促进催化反应的进行。Cu-Mn/SAPO-34/1∶4具备丰富的酸性位、良好的氧化还原性能和抗SO_2/H_2O性能,该配比有助于催化剂的催化活性和稳定性的提高。  相似文献   

12.
采用浸渍法制备系列铜铈复合氧化物分子筛催化剂(Cu-Ce/SAPO-34),探讨了Ce负载量对Cu/SAPO-34催化剂的水热稳定性的影响,通过XRD、SEM、H2-TPR、XPS和NH3-TPD等表征手段分析不同催化剂活性和稳定性差异的原因。研究表明,750℃水热老化未造成Cu-Ce/SAPO-34催化剂菱沸石(chabazite,CHA)骨架坍塌,但破坏了部分孔结构和酸性位点,使催化剂表面结晶度下降。水热老化促使催化剂晶格发生拉伸畸变,使Cu2+迁移到催化剂表面,Cu2+和Ce4+团簇形成CuO和CeO2,造成催化剂的Cu活性物种减少和氧空穴浓度降低,所以Cu-Ce/SAPO-34的NH3选择性催化还原(NH3-Selective Catalytic Reduction,NH3-SCR)性能下降。掺杂Ce能提高Cu/SAPO-34催化剂表面的Cu2+和Cu+活性物种量,减少Cu物种团簇形成CuO,改善催化剂表面活性Cu物种分布性。提高Ce的负载量能稳固Cu-Ce/SAPO-34催化剂的结构,使中、弱强度酸位点得以维持,从而提高其水热稳定性。结果表明,在研究的系列Cu-Ce/SAPO-34催化剂中,Cu/Ce质量比为4:5时具有最佳的水热稳定性。  相似文献   

13.
选用不同种类的铵盐和调变Cu2+离子交换时间制备不同铜交换量的Cu-SAPO-34催化剂。并考察了铜交换量对催化剂在氨选择性催化还原(NH3-SCR)NOx反应中的催化性能和高温水热稳定性的影响。结果表明,Cu2+是Cu-SAPO-34催化剂在NH3-SCR反应中的主要活性中心,随着Cu交换量的增加催化剂的低温SCR活性先升高后降低。铜交换量为2.37%时,Cu-SAPO-34催化剂的低温活性最好,NOx转化率在185℃时即可达到80.0%,且最高达98.7%。ICP、H2-TPR、FT-IR和NH3-TPD等表征结果显示,Cu引入不但产生了新的氨吸附位点,增加了Lewis酸量,而且略微降低了SAPO-34上氨的吸附强度。继续增加Cu交换量反而导致催化剂的SCR活性下降,这是由于大量的Cu2+取代了桥式羟基Si-OH-Al中的H,抑制了SCR反应中NH3在催化剂表面的吸附、储存与迁移。此外,较高Cu交换量也不利于改善Cu-SAPO-34的高温水热稳定性。  相似文献   

14.
The effect of potassium(K) promoter on the catalytic performance of activated carbon(AC) supported Wacker-type catalysts(Pd Cl2–Cu Cl2/AC) for the synthesis of dimethyl carbonate(DMC) from CO and methyl nitrite(MN) was investigated by means of N2 adsorption, H2-temperature-programmed reduction(H2-TPR), and X-ray photoelectron spectroscopy(XPS). The experimental results showed that the space time yield of DMC on Wacker-type catalysts with different K promoters ranked in the following order: KCl KOH CH3 COOK K2CO3. Especially, the addition of KCl significantly improved the catalytic activities of Pd Cl2–Cu Cl2/AC catalyst for DMC synthesis from CO and MN. N2 adsorption data indicated that the addition of K promoters did not change the textural properties of Wacker-type catalysts greatly. H2-TPR and XPS results demonstrated that the existence of KCl promoted the reducibility of Cu2+species and increased the proportion of Cu2+species on catalyst surface, which is favorable for oxidizing Pd0 to active Pd2+. Further, the addition of KCl benefited the reactivity of Pd Cl2–Cu Cl2/AC catalyst for DMC synthesis from CO and MN.  相似文献   

15.
分别以Al2O3, SiO2和C3N4为载体, 通过简单浸渍法制备了3种负载型Pd-Cu催化剂(PC-Al2O3, PC-SiO2, PC-C3N4), 考察了其在室温下富氢气氛中CO优先氧化反应性能. 采用X射线衍射(XRD)、 傅里叶变换红外光谱(FTIR)、 氮气物理吸附仪(N2-physisorption)、 氢气程序升温还原(H2-TPR)、 二氧化碳程序升温脱附(CO2-TPD)、 X射线光电子能谱(XPS)和原位漫反射傅里叶变换红外光谱(In situ DRIFTS)等手段对其进行了表征. 结果表明, 与PC-SiO2和PC-C3N4相比, PC-Al2O3具有更高的CO优先氧化性能. 这是由于PC-Al2O3上形成了大量与Pd物种具有强相互作用的Cu2Cl(OH)3物种; 而PC-SiO2中仅有少量的Cu2Cl(OH)3, 且与Pd物种相互作用较弱; PC-C3N4中Cu物种则更易与C3N4基质配位, 由此削弱了Pd, Cu之间的相互作用. 在反应气氛下PC-Al2O3表面还易形成具有更强CO活化能力的Pd+物种, 通过与大量Cu+物种紧密相互作用, 在一定程度上抑制Pd+被过度还原为Pd0, 从而维持了其催化活性. 与SiO2和C3N4相比, Al2O3更适合负载Pd-Cu用于富氢气氛下CO优先氧化反应.  相似文献   

16.
龚文朋  陈丹  杨水金 《应用化学》2017,34(11):1321-1328
以2-氨基对苯二甲酸、4,4'-联吡啶配体和硝酸铜为原料,在溶剂热的条件下,合成了一种的阴离子型三维金属有机框架(MOF)材料Cu(BDC-NH_2)(4,4'-Bipy)_(0.5)(BDC=对苯二甲酸根,Bipy=联吡啶)。通过IR、XRD、SEM、TG、N_2吸附法测比表面积等技术手段表征材料的结构和性能。研究了Cu(BDC-NH_2)(4,4'-Bipy)_(0.5)材料对甲基紫的吸附性能,探讨了甲基紫溶液的初始p H值和初始浓度以及不同吸附温度对吸附量的影响。结果表明,等温吸附模型符合Langmuir等温吸附模型,动力学符合拟二级动力学。热力学参数ΔG0、ΔΗ0和ΔS0,表明Cu(BDC-NH_2)(4,4'-Bipy)_(0.5)对甲基紫的吸附是自发和放热的,在溶液p H=9,温度为20℃条件下,Cu(BDC-NH_2)(4,4'-Bipy)_(0.5)对甲基紫的吸附量为60.09 mg/g,说明Cu(BDC)(4,4'-Bipy)_(0.5)材料可以通过氨基改性,提高其对染料的吸附能力。  相似文献   

17.
Electronic chemiluminescence from the reaction of selected ground state (2S1/2) or metastable (2D5/2, 2D3/2) copper atoms with fluorine has been studied using a hollow cathode-flowing afterglow reactor. The observed signal related to the Cu(2S) and Cu*(2D) atom densities, indicate that the chemiluminescence cross-section for Cu*(2D) atoms is about 104 times larger than for Cu(2S) atoms. This strong propensity is explained in terms of a direct reaction, initiated by a harpooning process, during which the Cu+ ion core of the reactant (3d10 for Cu(2S) and 3d94s for Cu*(2D)) is conserved in the products (ionic structure Cu+(3d10)F for the CuF ground state and Cu+(3d94s)F for the CuF*(a, A, B, C, D) chemiluminescent states).  相似文献   

18.
Silver nanoplates as novel optical sensors for Cu^2+ detection have been demonstrated.Silver nanoplates are synthesized via previous H_2O_2-NaBH_4 cyclic oxidation-reduction reactions.With introduction of ascorbate as mild reductants,Cu^2+ ions are reduced into Cu~+ and the Cu^+ is further reduced to Cu,which is deposited on the surface of the silver nanoplates.The deposition of the Cu on the surface of the silver nanoplates allows a significant red-shift of their plasmon absorption.Therefore,trace Cu^2+ can be detected.The shift of the plasmon absorption wavelength of silver nanoplates is proportional to the Cu^2+concentration over a range of 40-340 μmol L~(-1) with a limit of detection of 9.0 μmol L~(-1).Moreover,such silver nanoplate-based optical sensors provide good selectivity for Cu^2+ detection,and most other metal ions do not disturb its detection.Moreover,the practicality of the proposed sensor was tested.This Cu^2+assay is advantageous in its simplicity,selectivity,and cost-effectiveness.  相似文献   

19.
A novel magnetic weak acid resin NDMC-1 was prepared in the presence of methyl acrylate(MA),divinylbenzene(DVB) and titanate coupling agent(TCA) coated 7-Fe2O3 particles.To evaluate the adsorption of Cu2+ on the obtained resin NDMC-1,another two magnetic resins NDMC-0(the precursor of NDMC-1 without hydrolyzation) and NDMO-l(the synthesized weak acid resin using oleic acid coatedγ-Fe2O3) were chosen for comparison.The results showed that the carboxyl groups were formed after hydrolyzation,and NDMC-1 exhibited a greater adsorption capacity to Cu2+.The desorption experiment demonstrated that the desorption ratio at pH 2(95.14%) was greatly higher than pH 3(25.97%).Moreover,the magnetic resin NDMC-1 was proved to be stable at pH 2,extending the application of magnetic materials which were always considered to be acid-nonresistant.  相似文献   

20.
通过在锐钛矿TiO_2载体表面上负载Cu-BTC(BTC,1,3,5-苯甲酸)前驱体,还原处理制备光催化剂CuO-Ti~(3+)/TiO_2(Cu-TiMB),对其在可见光条件下气相甲苯净化催化性能进行了研究。结果表明,该改良方法制备的CuO-Ti~(3+)/TiO_2(CuTiM B)催化剂的活性是浸渍法所得催化剂CuO-TiO_2(Cu-TiD)的2.68倍。CuO-Ti~(3+)/TiO_2(Cu-TiMB)具有更大的比表面积(147 m2/g)和较小的颗粒粒径(0.45μm),呈现多孔状,CuO的分散度较高;催化剂表面Ti~(3+)提供了大量的氧缺位,在400-800 nm波段的光响应能力显著增强。CuO-Ti~(3+)/TiO_2(Cu-TiMB)催化剂中Cu~(2+)、Cu~+与Ti~(3+)形成的异质结构进一步增多了氧缺位数量,延缓e--h+的复合时间;氧缺陷增强了捕获吸附氧能力,通过金属氧化物价态变化增强化学吸附能力,提高了光催化性能。  相似文献   

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