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1.
Comparison is made between Cu–ZnO and alumina-supported Cu–ZnO as catalysts for the reverse water-gas shift (RWGS) reaction. For both types of catalyst the Cu/Zn ratio has been varied between Cu-rich and Zn-rich compositions. By applying X-ray diffractometry, X-ray line broadening, optical reflectance spectroscopy and other techniques the effects on the structural and physical properties of the hydroxycarbonate precursors, the calcined products and the ultimately derived catalysts are determined. The presence of alumina decreases the crystallite size of the CuO and ZnO particles produced on calcination and at high Cu/Zn ratios increases the dispersion of copper in the final catalyst. The activities of the catalysts for the RWGS reaction at 513K are compared and the most active are shown to be those which are Cu rich (Cu/Zn > 3) and contain alumina as support. The activities of all the catalysts can be rationalized by referring the activity to unit surface area of copper metal. 相似文献
2.
Ruichao Zhang Hengbo Yin Dongzhi Zhang Lin Qi Huihong Lu Yutang Shen Tingshun Jiang 《Chemical engineering journal (Lausanne, Switzerland : 1996)》2008,140(1-3):488-496
Cu/ZnO/TiO2 catalysts were prepared via the coprecipitation method. The catalysts were characterized by X-ray diffraction, X-ray photoelectron spectrometry, temperature programmed reduction, and N2 adsorption. The catalytic activity of Cu/ZnO/TiO2 catalyst in gas phase hydrogenation of maleic anhydride in the presence of n-butanol was studied at 235–280 °C and 1 MPa. The conversion of maleic anhydride was more than 95.7% and the selectivity of tetrahydrofuran was up to 92.7%. At the same time, n-butanol was converted to butyraldehyde and butyl butyrate via reactions, namely, dehydrogenation, disproportionation, and esterification. There were two kinds of CuO species present in the calcined Cu/ZnO/TiO2 catalysts. At a lower copper content, the CuO species strongly interacted with ZnO and TiO2; at a higher copper content, both the surface-anchored and bulk CuO species were present. The metallic copper (CuO) produced by the reduction of the surface-anchored CuO species favored the deep hydrogenation of maleic anhydride to tetrahydrofuran. The deep hydrogenation activity of Cu/ZnO/TiO2 catalyst increased with the decrease of crystallite sizes of CuO and the increase of microstrain values. Compensations of reaction heat and H2 in the coupling reaction of maleic anhydride hydrogenation and n-butanol dehydrogenation were distinct. 相似文献
3.
Implication of the microstructure of binary Cu/ZnO catalysts for their catalytic activity in methanol synthesis 总被引:2,自引:0,他引:2
M.M. Günter T. Ressler B. Bems C. Büscher T. Genger O. Hinrichsen M. Muhler R. Schlögl 《Catalysis Letters》2001,71(1-2):37-44
Binary Cu/ZnO catalysts with varying molar ratios (90/10 through 10/90) were studied under methanol synthesis conditions at 493 K and at atmospheric pressure. The methanol synthesis activity of the catalysts was correlated to their specific Cu surface area (N2O reactive frontal chromatography, N2O RFC) after reduction in 2 vol% H2 at 513 K. Activity data were supplemented with a detailed analysis of the microstructure, i.e., crystallite size and strain of the reduced Cu and the ZnO phases after reduction using X-ray diffraction line profile analysis. The estimated copper surface area based on a spherical shape of the copper crystallites is in good agreement with data determined by N2O RFC. A positive correlation of the turnover frequency for methanol production with the observed microstrain of copper in the Cu/ZnO system was found. The results indicate a mutual structural interaction of both components (copper and zinc oxide) in the sense that strained copper particles are stabilized by the unstrained state of the zinc oxide microcrystallites. The observed structural deformation of ZnO in samples with higher Cu loading can originate, for instance, from epitaxial bonding of the oxide lattice to the copper metal, insufficient reduction or residual carbonate due to incomplete thermal decomposition during reduction. Additional EXAFS measurements at the Cu K and the Zn K edge show that about 5% ZnO are dissolved in the CuO matrix of the calcined precursors. Furthermore, it is shown that the microstructural changes (e.g., size and strain) of copper can be traced back to the phase composition of the corresponding hydroxycarbonate precursors. 相似文献
4.
In this work the results of a TPR and XPS investigation of CoxOy–CuO mixed oxides in the range of composition Co : Cu=100:0–8:92 are reported and compared. The final catalysts were obtained by thermal decomposition in air and N2 at 723 K for 24 h of singlephase cobalt–copper hydroxycarbonates prepared by coprecipitation at constant pH. The Co : Cu=100 : 0 specimen calcined in air formed the Co2+[Co3]2O4 (Co3O4) spinel phase. The coppercontaining catalysts (Co : Cu=85 : 15–8 : 92) showed mainly two phases: (i) spinels, like Co2+[Co3+]2O4, Co
1-x
2+
Cu
x
2+
[Co3+]2O4 and (ii) pure CuO, the relative amount of each phase depending on the Co : Cu atomic ratio. The results of the XPS study are consistent with the bulk findings and revealed the presence of Co2+, Co3+ and Cu2+ species at the catalyst surface. Moreover, the surface quantitative analysis evidenced a cobalt enrichment, in particular for the most diluted cobalt samples. The TPR study showed that the catalyst reduction is affected by a strong mutual influence between cobalt and copper. The reducibility of the mixed oxide catalysts was always promoted with respect to that of the pure Co3O4 and CuO phases and the reduction of cobalt was markedly enhanced by the presence of copper. Cobalt and copper were both reduced to metals regardless of the catalyst composition. On the other hand, the Co : Cu=100 : 0 specimen calcined in N2 formed, as expected, CoO. The initial addition of copper resulted in the formation of the Cu+Co3+O2 compound, besides CoO, up to a Co/Cu=1 atomic ratio at which the CuCoO2 phase was the main component. A further addition of copper led to the formation of CuCoO2 and CuO phases. The XPS results were in good agreement with these findings and the surface quantitative analysis revealed a less enrichment of cobalt with respect to the catalysts calcined in air. The TPR analysis confirmed that the reduction of the N2calcined catalysts was also remarkably promoted by the presence of copper. Also in this case cobalt and copper metal were the final products of reduction. 相似文献
5.
Isothermal hydrogen interaction with unsupported CuO and 15%CuO/ZnO at about 419–427 K has been followed by in-situ X-ray diffraction as monoclinic CuO is replaced by zero-valent Cu° without direct evidence of formation of intermediate Cu2O. Surprisingly, less than half of the copper phases within such samples is X-ray detectable. X-ray analysis indicates that reduction of crystalline CuO in CuO/ZnO catalysts may not be retarded by ZnO, but TPR-TGA suggests that reduction of more amorphous CuO may be so retarded. 相似文献
6.
Linear potential sweep voltammetry was used to characterize the copper oxides grown on a metal substrate when exposed to a low pressure inductively coupled oxygen plasma. This study confirms the formation of a precursor oxide CuxO (x > 4), two copper(i) oxides Cu2-xO and Cu3O2 and copper(ii) oxide CuO. The electrochemical reduction curve of CuxO is characterized in aqueous solution (pH 9.2) by a minor peak near –0.5V vs SCE while the two Cu(i) oxides present one reduction peak at –0.8 VvsSCE and cannot be electrochemically separated; CuO is reduced to Cu(i) at –0.65V vs SCE. The reduction potentials of the copper(i) and copper(ii) oxides vary with the oxide layer thickness which increases with the time of exposure to the plasma and the injected electric power and decreases as the distance between the sample and the 1st coil increases for given treatment parameters. In addition, a mechanism is proposed for the reduction of thin films containing the copper(i) and copper(ii) oxides formed after plasma treatment. 相似文献
7.
8.
《Catalysis communications》2007,8(2):193-199
Cu–Zn–Ti catalysts were prepared by coprecipitation method. The calcined and reduced Cu–Zn–Ti catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), and N2 adsorption. The calcined Cu–Zn–Ti catalysts were composed of CuO, ZnO, and amorphous TiO2. There were two kinds of CuO species present in the calcined Cu–Zn–Ti catalyst. At a lower copper content, CuO species interacted with ZnO and TiO2; at a higher copper content, both the surface-anchored and bulk CuO species were present. After reduction, metallic copper (Cuo) appeared in all Cu–Zn–Ti catalysts. Cuo produced by reduction of the surface-anchored CuO favored the deep hydrogenation of maleic anhydride. ZnO and TiO2 had synergistic effect on the catalytic activity of Cu–Zn–Ti catalysts in hydrogenation of maleic anhydride. 相似文献
9.
For the dehydrogenation of cyclohexanol a series of Cu–ZnO/SiO2 catalysts with various Cu to ZnO molar ratios was prepared using the impregnation method, with the loading of copper fixed at 9.5 at.%. The catalysts were characterized by XPS, H2–N2O titration, BET, H2-TPR, NH3-TPD and XRD techniques. The results indicate that the addition of ZnO can improve the dispersion of copper species on reduced Cu–ZnO/SiO2 (CZS) catalysts. Cu0 and Cu+ species were found on the reduced CZS catalysts surface, and the amount of Cu+ increased with the content of ZnO increasing. The addition of ZnO increased the acidity of the CZS catalysts. However, only Cu0 species can be found on the reduced Cu/SiO2 (CS) catalyst surface. According to the reaction results, we found that the selectivity to phenol was related to the amount of Cu+ species, the Cu+ species should be the active sites for the production of phenol, the Cu0 is responsible for cyclohexanol dehydrogenation to cyclohexanone. 相似文献
10.
Lianjun Liu Bin Liu Lihui Dong Jie Zhu Haiqin Wan Keqin Sun Bin Zhao Haiyang Zhu Lin Dong Yi Chen 《Applied catalysis. B, Environmental》2009,90(3-4):578-586
In situ FT-IR was employed to investigate CO or/and NO interaction with CuO supported on Ce0.67Zr0.33O2 (hereafter denoted as CZ) catalysts. The physicochemical properties of CuO–CZ were also studied by combination of XRD, TPR and NO + CO activity tests. The results indicated that the dispersed CuO species were the main active components for this reaction. The catalysts showed different activities and selectivities at low and high temperatures, which should be resulted from the reduction of dispersed copper oxide species. This reaction went through different mechanisms at low and high temperatures due to the change of active species. FT-IR results suggested: (1) CO was activated by oxygen originating from CZ support, which led to surface carbonates formation, and partial dispersed CuO was reduced to Cu+ species above 150 °C; (2) NO interacted with the dispersed CuO and formed several types of nitrite/nitrate species, whereas crystalline CuO made little contribution to the formation of new NO adsorbates; (3) NO was preferentially adsorbed on CuO–CZ catalysts compared with CO in the reactants mixture. These adsorbed nitrite/nitrate species exhibited different thermal stability and reacted with CO at 250 °C. As a result, a possible mechanism was tentatively proposed to approach NO reduction by CO over CuO–CZ catalyst. 相似文献
11.
《Journal of Industrial and Engineering Chemistry》2014,20(3):925-929
Nanostructure CuO/ZnO mixed oxide was systematically prepared via the sol–gel route using zinc and copper carbonates as precursors (molar ratio of 2:1) under thermal decomposition. The zinc and copper carbonates precursors have been synthesized by a simple chemical reaction in high yield and characterized by its melting point, FT-IR and thermal analysis (TG/DTG). The TG/DTG analysis proved that the thermal decomposition of zinc and copper carbonates precursors at 255 °C and 289 °C respectively. Thermo-gravimetric analysis (TG-DTG), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and diffuse reflectance spectroscopy (DRS) studies were undertaken to investigate the thermal properties and electronic structure of the CuO/ZnO mixed oxide catalysts. XRD data of the samples proved the formation of the nano-crystalline CuO/ZnO mixed oxide. Scanning electron microscopy (SEM) showed that the spherical-like particles have a diameter in the range 35–45 nm. Optical spectra of the nanostructure show a band peaked at 1.35 eV which is associated to near band gap transitions of CuO and a band centered at about 3.00 eV related to band gap transitions of ZnO nanostructures. 相似文献
12.
以氧化铝为载体,采用浸渍法制备了负载型CuO-ZnO/Al2O3催化剂,通过XRD、XPS、TPR手段表征催化剂上CuO和ZnO的分布和化学形态。结果表明,CuO-ZnO/Al2O3催化剂催化甘油氢解反应中,CuO是活性组分,ZnO的引入可以降低CuO与载体氧化铝的相互作用强度,有利于CuO的还原,提高催化剂甘油氢解活性;催化剂表面呈缺电子状态的Cu物种是甘油氢解的活性中心。当活性组分CuO质量分数为12%,n(Cu)∶n(Zn)=1∶1.5时,CuO-ZnO/Al2O3催化剂催化甘油氢解活性最高,甘油转化率可达97.82%,对1,2-丙二醇选择性达94%。 相似文献
13.
Aritomo Yamaguchi Takafumi Shido Yasuhiro Inada Toshihiro Kogure Kiyotaka Asakura Masaharu Nomura Yasuhiro Iwasawa 《Catalysis Letters》2000,68(3-4):139-145
The time-resolved reduction process of copper cations in/on ZSM-5 during temperature-programmed reduction (300–700 K) was studied by energy-dispersive X-ray absorption fine structure (DXAFS) as well as transmission electron microscopy (TEM). Two Cu-ZSM-5 samples with different Cu loadings were prepared by an ion-exchange method. The Cu K-edge DXAFS spectra for isolated Cu2+ species in the channels of ZSM-5 and CuO particles on the outer surfaces of ZSM-5 were recorded at an interval of 1 s during the reduction. The curve fitting analysis of the EXAFS data and the XANES analysis revealed that the isolated Cu2+ species in the channels were reduced stepwise. They were reduced to isolated Cu+ species at 400–450 K and the Cu+ species to Cu0 metallic clusters at 550–650 K. Small clusters like Cu4 were initially formed, followed by particle growth. A small part of them went out to the outer surfaces of ZSM-5 during the reduction. In contrast, CuO particles on the outer surfaces were reduced directly to Cu0 metallic particles around 450 K. 相似文献
14.
B. Montanari A. Vaccari M. Gazzano P. Kßner H. Papp J. Pasel R. Dziembaj W. Makowski T. Lojewski 《Applied catalysis. B, Environmental》1997,13(3-4):205-217
Cu/Mg/Al mixed oxides (CuO = 4.0–12.5 wt%), obtained by calcination of hydrotalcite-type (HT) anionic clays, were investigated in the selective catalytic reduction (SCR) of NO by NH3, either in the absence or presence of oxygen, and their behaviours were compared with that of a CuO-supported catalyst (CuO = 10.0 wt%), prepared by incipient wetness impregnation of a Mg/Al mixed oxide also obtained by calcination of an HT precursor. XRD analysis, UV-visible-NIR diffuse reflectance spectra and temperature-programmed reduction analyses showed the formation, in the mixed oxide catalysts obtained from HT precursors, mainly of octahedrally coordinated Cu2+ ions, more strongly stabilized than Cu-containing species in the supported catalyst, although the latter showed a lower percentage of reduction. The presence of well dispersed Cu2+ ions improved the catalytic performances, although similar behaviours were observed for all catalysts in the absence of oxygen. On the contrary, when the mixture with excess oxygen was fed, very interesting catalytic performances were obtained for the catalyst richest in copper (CuO = 12.5 wt%). This catalyst exhibited a behaviour comparable to that of a commercial V2O5–WO3TiO2 catalyst, without any deactivation phenomena after four consecutive cycles and following 8 h of time-on-stream at 653 K. Decreasing the copper content or increasing the calcination time and temperature led to considerably poorer performances and catalytic behaviours similar to that of the CuO-supported catalyst, due to the side-reaction of NH3 combustion on the free Mg/Al mixed oxide surface. 相似文献
15.
The electrochemical behaviour of Cu–Zn–Al oxide catalysts in a high-temperature solvent, dimethylsulphone (DMSO2), at 150°C has been investigated. It has been shown that CuO electroreduction becomes easier and/or deeper in the Cu–Zn–Al oxide catalysts than in CuO alone. This electroreduction occurs at higher potentials, and the overall faradic yield decreases when CO2 in dissolved in DMSO2 on account of a strong interaction between the reduced species formed during the electronic transfer and CO2. These results are consistent with the characterizations of the physical and chemical properties of these catalysts. They confirm that electrochemistry is a suitable method to determine the redox states of some copper industrial catalysts used in methanol synthesis. 相似文献
16.
Nachal Devi Subramanian G. Balaji Challa S.S.R. Kumar James J. Spivey 《Catalysis Today》2009,147(2):100
The synthesis of higher alcohols from syngas has been studied over different types of Cu-based catalysts. In order to provide control over the catalyst composition at the scale of a few nanometers, we have synthesized two sets of Co–Cu nanoparticles with novel structures by wet chemical methods, namely, (a) cobalt core–copper shell (Co@Cu) and (b) cobalt–copper mixed (synthesized by simultaneous reduction of metal precursors) nanoparticles. These catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and temperature programmed reduction (TPR). The catalysts were tested for CO hydrogenation at temperatures ranging from 230 °C to 300 °C, 20 bar and 18,000 scc/(hr.gcat). It was observed that the Co–Cu mixed nanoparticles with higher Cu concentration exhibit a greater selectivity towards ethanol and C2+ oxygenates. The highest ethanol selectivity achieved was 11.4% with corresponding methane selectivity of 17.2% at 270 °C and 20 bar. 相似文献
17.
A palladium–copper–zinc catalyst (PdO:CuO:ZnO=2:28:70), prepared by sequential precipitation of the respective cations, was tested in the hydrogenation of CO2 at high pressure (conditions: 60 bar, CO2:H2=1:3 (molar), W/F=0.0675 kg h/m3, 453-513 K). The methanol yield was improved on using this Pd-containing catalyst at all temperatures with respect to the reference copper–zinc catalyst (CuO:ZnO=30:70). This improvement was not due to an additional effect in which palladium was acting as an independent catalytic site but was caused by a synergetic effect of Pd on the active Cu sites. This effect was explained in terms of hydrogen spillover and an increased stability against CO2 oxidation of the surface copper. Therefore, the present contribution not only supports previous literature findings concerning the hydrogen spillover mechanism but also resulted in a complementary view regarding the role of palladium in Pd-modified CuO-ZnO-based catalysts. 相似文献
18.
M. W. E. van den Berg S. Polarz O. P. Tkachenko K. Kähler M. Muhler W. Grünert 《Catalysis Letters》2009,128(1-2):49-56
A systematic series of model methanol synthesis catalysts was prepared by sequential impregnation of a mesoporous silica material (5 nm average pore size) with an organometallic ZnO precursor which is liquid at room temperature, followed by the infiltration with an aqueous Cu nitrate solution. These catalysts, which contained 14–20 wt.% Cu and 1–5 wt.% Zn, were characterized by N2O reactive chemisorption, by EXAFS and by measuring their methanol synthesis activities. It was observed that the formation of confined, nanocrystalline ZnO prior to copper infiltration is of major importance for the development of catalyst activity. Severe reduction of properly prepared catalysts (10% CO/H2, 673 K, 15 min) leads to the emergence of a new feature in the ZnK EXAFS spectrum which was assigned to a Cu neighbour by combined evidence from the ZnK EXAFS and XANES regions. The zinc oxide component was partially reduced as well, but Zn(0) was not formed to any significant extent. Catalysts which developed this Cu–Zn2+ interaction under severe reduction were superior in terms of methanol synthesis rate per m2 Cu surface area to a sample which did not exhibit this feature. 相似文献
19.
The synthesis of methanol on a Cu(100) single crystal surface was studied between 500–550 K and at pressures between 44–102 kPa using a gas mixture of CO2/CO/H2 = 1/2/12. The specific reaction rates found for methanol synthesis were approximately an order of magnitude lower than those rates previously reported for silica supported, Cu-based catalysts. Furthermore the rates observed for the Cu(100) catalyst are estimated to be several orders of magnitude smaller than those rates found for ZnO supported Cu catalysts at comparable reaction conditions. The very low concentration of ionic copper species on the surface is thought to be responsible for the low activity of the Cu(100) catalyst. 相似文献
20.
In this paper, the microstructure of a 1 wt.% Cu/γ-Al2O3 catalyst that was reduced in a 4% hydrogen/argon atmosphere at temperatures of 523, 773 and 1073 K, is studied by Z-contrast imaging and electron energy-loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM). Results show that the copper species are well dispersed when the catalyst is reduced below 523 K. At 773 K, separated Cu(I) and Cu(0) species are found existing as ring-like and bulk-like particles. This appears to indicate that the copper has not been reduced to its metallic form due to the interaction between the copper oxide and the support. Large spherical particles having core-shell structures with Cu(I) in the shells and Cu(0) in the cores are generated when the catalyst is reduced at 1073 K. The formation of partially oxidized copper species upon reduction at 1073 K is attributed to the metallic copper interaction with the alumina support. This study also demonstrates that high-spatial resolution Z-contrast imaging and EELS performed simultaneously can provide unique information on the morphology and chemistry of metal species in supported metal catalysts. 相似文献