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1.
The catalytic performance of mono- and bimetallic Pd (0.6, 1.0 wt.%)–Pt (0.3 wt.%) catalysts supported on ZrO 2 (70, 85 wt.%)–Al 2O 3 (15, 0 wt.%)–WO x (15 wt.%) prepared by sol–gel was studied in the hydroisomerization of n-hexane. The catalysts were characterized by N 2 physisorption, XRD, TPR, XPS, Raman, NMR, and FT-IR of adsorbed pyridine. The preparation of ZrW and ZrAlW mixed oxides by sol–gel favored the high dispersion of WO x and the stabilization of zirconia in the tetragonal phase. The Al incorporation avoided the formation of monoclinic-WO 3 bulk phase. The catalysts increased their SBET for about 15% promoted by Al 2O 3 addition. Various oxidation states of WO x species coexist on the surface of the catalysts after calcination. The structure of the highly dispersed surface WO x species is constituted mainly of isolated monotungstate and two-dimensional mono-oxotungstate species in tetrahedral coordination. The activity of Pd/ZrW catalysts in the hydroisomerization of n-hexane is promoted both with the addition of Al to the ZrW mixed oxide and the addition of Pt to Pd/ZrAlW catalysts. The improvement in the activity of Pd/ZrAlW catalysts is ascribed to a moderated acid strength and acidity, which can be correlated to the coexistence of W 6+ and reduced-state WO x species (either W 4+ or W 0). The addition of Pt to the Pd/ZrAlW catalyst does not modify significantly its acidic character. Selectivity results showed that the catalyst produced 2MP, 3MP and the high octane 2,3-dimethylbutane (2,3-DMB) and 2,2-dimethylbutane (2,2-DMB) isomers. 相似文献
2.
ZrO 2-doped CuZnO catalyst prepared by successive-precipitation method was investigated by ICP-AES, BET, TEM, XRD, EXAFS, H 2-TPR and CO/CO 2 hydrogenation. The active phase of copper in CuZnO catalyst prepared by co-precipitation method was well-crystallized. The presence of ZrO 2 led to a high copper dispersion, which was distinctive from CuZnO. Though the activity for carbon monoxide hydrogenation was little lower than that of CuZnO catalyst, ZrO 2-doped CuZnO catalyst showed much higher activity and selectivity towards methanol synthesis from carbon dioxide hydrogenation. Moreover, ZrO 2-doped CuZnO catalyst showed high performance for methanol synthesis from CO 2-rich syngas. 相似文献
3.
Cu/ZrO 2 catalysts for methanol synthesis from CO 2/H 2 were respectively prepared by deposition coprecipitation (DP) and solid state reaction (SR) methods. There is an intimate interaction between copper and zirconia, which strongly affects the reduction property and catalytic performance of the catalysts. The stronger the interaction, the lower the reduction temperature and the better the performance of the catalysts. Surface area, pore structure and crystal structure of the catalysts are mainly controlled by preparation methods and alkalinity of synthesis system. The conversion of CO 2 and selectivity of methanol are higher for DP catalysts than for SP catalysts. 相似文献
4.
CaO–ZrO 2 catalysts were prepared by coprecipitation and their catalytic performances were evaluated in the synthesis of dimethyl carbonate from propylene carbonate and methanol. The characterization by XRD, N 2 adsorption, XPS and CO 2–TPD indicated that Ca 2+ ion substituted for Zr 4+ ions in the host lattice to form homogeneous CaO–ZrO 2 solid solution when Ca/(Ca + Zr) ratio changed from 0.1 to 0.3, and CaO segregated at grain boundaries with Ca/(Ca + Zr) ratio from 0.4 to 0.5. As a result, the catalysts showed different activity and stability towards the transesterification of propylene carbonate and methanol into dimethyl carbonate. The activity of catalysts was improved with increase in Ca content, whereas high stability was shown with Ca/(Ca + Zr) ratio below 0.3. The formation of homogeneous CaO–ZrO 2 solid solution was responsible for the stability of catalysts. 相似文献
5.
The NiSO 4 supported on Fe 2O 3-promoted ZrO 2 catalysts were prepared by the impregnation method. Fe 2O 3-promoted ZrO 2 was prepared by the coprecipitation method using a mixed aqueous solution of zirconium oxychloride and iron nitrate solution followed by adding an aqueous ammonia solution. No diffraction line of nickel sulfate was observed up to 20 wt.%, indicating good dispersion of nickel sulfate on the surface of Fe 2O 3–ZrO 2. The addition of nickel sulfate (or Fe 2O 3) to ZrO 2 shifted the phase transition of ZrO 2 (from amorphous to tetragonal) to higher temperatures because of the interaction between nickel sulfate (or Fe 2O 3) and ZrO 2. 15-NiSO 4/5-Fe 2O 3–ZrO 2 containing 15 wt.% NiSO 4 and 5 mol% Fe 2O 3, and calcined at 500 °C exhibited a maximum catalytic activity for ethylene dimerization. NiSO 4/Fe 2O 3–ZrO 2 catalysts was very effective for ethylene dimerization even at room temperature, but Fe 2O 3–ZrO 2 without NiSO 4 did not exhibit any catalytic activity at all. The catalytic activities were correlated with the acidity of catalysts measured by the ammonia chemisorption method. The addition of Fe 2O 3 up to 5 mol% enhanced the acidity, surface area, thermal property, and catalytic activities of catalysts gradually, due to the interaction between Fe 2O 3 and ZrO 2 and due to consequent formation of Fe–O–Zr bond. 相似文献
6.
采用溶胶-凝胶法以铜、锌、锆硝酸盐和柠檬酸为原料,改变柠檬酸用量,制备出一系列Cu-ZnO-ZrO 2催化剂。通过X射线衍射仪(XRD)、热重分析仪(TG-DTG-DTA)、H 2程序升温还原(H 2-TPR)、CO 2程序升温脱附(CO 2-TPD)、红外光谱仪(FTIR)及BET比表面积等表征手段对干凝胶及催化剂理化性能进行测试,并在催化反应活性评价装置上对催化剂的CO 2加氢合成甲醇反应活性进行评价,研究凝胶过程中Cu 2+、Zn 2+、Zr 4+与柠檬酸结合方式对催化剂性能的影响。结果表明:改变柠檬酸用量可调控Cu 2+、Zn 2+、Zr 4+与羧酸的配位方式,配位能力较强的Cu 2+、Zn 2+在凝胶制备过程中参与三维网络的构筑,而配位能力相对较弱的Zr 4+游离于三维网络之外,从而差异化地调控催化剂中活性组分CuO、ZnO、ZrO 2晶粒尺寸大小。当柠檬酸的摩尔量为金属离子摩尔量的1.5倍时,催化剂中的活性成分CuO、ZnO、ZrO 2晶粒尺寸相互匹配,表现出较好的CO 2加氢合成甲醇催化性能。 相似文献
7.
This work investigates the effects of Au 3+/Au 0 ratio or distribution of gold oxidation states in Au/ZrO 2 catalysts of different gold loadings (0.01–0.76% Au) on CO oxidation and 1,3-butadiene hydrogenation by regulating the temperature of catalyst calcination (393–673 K) and pre-reduction with hydrogen (473–523 K). The catalysts were prepared by deposition–precipitation and were characterized with elemental analysis, nitrogen adsorption/desorption, TEM, XPS and TPR. The catalytic data showed that the exposed metallic Au 0 atoms at the surface of Au particles were not the only catalytic sites for the two reactions, isolated Au 3+ ions at the surface of ZrO 2, such as those in the catalysts containing no more than 0.08% Au were more active by TOF. For 0.76% Au/ZrO 2 catalysts having coexisting Au 3+ and Au 0, the catalytic activity changed differently with varying the Au 3+/Au 0 ratio in the two reactions. The highest activity for the CO oxidation reaction was observed over the catalyst of Au 3+/Au 0 = 0.33. However, catalyst with a higher Au 3+/Au 0 ratio showed always a higher activity for the hydrogenation reaction; co-existance of Au 0 with Au 3+ ions lowered the catalyst activity. Moreover, the coexisting Au particles changed the product selectivity of 1,3-butadiene hydrogenation to favor the formation of more trans-2-butene and butane. It is thus suggested that for better control of the catalytic performance of Au catalyst the effect of Au 3+/Au 0 ratio on catalytic reactions should be investigated in combination with the particle size effect of Au. 相似文献
8.
Promotional effects of chromia on the structure and activity of skeletal copper catalysts for methanol steam reforming and water gas shift have been studied. Catalysts were prepared by leaching CuAl 2 alloy particles in aqueous NaOH solutions containing sodium chromate at various concentrations. XPS spectra showed that the surface of the resulting catalysts mainly consisted of Cr 3+ compounds and Cu 0. Cu + and/or Cu 2+ were not observed by XPS. Increasing the concentration of chromate in the leach liquor resulted in decreases in pore diameter and copper crystallite size but significant enhancement of BET surface area was observed while the total pore volume was maintained. The addition of small amounts of chromate to the leach liquor significantly enhanced the Cu surface area. However, higher concentrations of chromate in the leach liquor decreased the Cu surface areas although the total surface areas increased. The activities of Cr2O3 promoted skeletal copper catalysts for both methanol steam reforming and water gas shift reactions were determined separately. The results indicated that deposition of Cr2O3 on skeletal copper catalysts significantly improved the specific activities for these reactions. Chromia is found to act as a structural and catalytic promoter for these reactions. 相似文献
9.
The local zirconium and iron arrangements of the iron-doped ZrO 2-TiO 2 system, prepared by sol–gel impregnation method, were studied by EXAFS spectroscopy. Only a tetragonal ZrO 2 structure is located on TiO 2 surface. For the iron-doped ZrO 2-TiO 2 system, the presence of the Fe-O-Fe species as well as and Fe-O-Zr species located on the surface/pre-surface region are shown; it seems that iron is heterogeneously distributed, forming small iron oxide nanoclusters and Fe x/ZrO 2 (tetragonal) spots at the catalyst surface. The photocatalytic activity of the un-doped and iron-doped binary system ZrO 2-TiO 2 was investigated in two kind of photoreactions: the salicylic acid photooxidation and the photocatalytic reduction of Cr(VI). Different photocatalytic behaviour has been found for the un-doped and iron-doped ZrO 2-TiO 2 systems which have been explained in terms of the EXAFS study. This study represents an example of attempt to prepare a new potential photoactive mixed oxide system, containing two ions (Ti4+ and Zr4+) with good photocatalytic activity if it is compared with commercial TiO2 (Degusssa P25) calcined at 600 °C. 相似文献
10.
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
11.
This paper presents the results of experiments of the methanol decomposition reaction catalyzed by a commercial Cu/ZnO/Al 2O 3 in the absence and presence of water. Methanol decomposition of 100% in the absence of water was obtained at 290 °C and a space velocity of 2 cm 3/h g cat. At these conditions, the hydrogen yield was 1.9–2.0. Water addition to the feed increased the yield of hydrogen and reduced the formation of: dimethyl ether; methyl formate and methane. The variation of the catalyst’s activity and selectivity with time, temperature and feed composition was consistent with previous studies of methanol–steam reforming and water–gas shift reaction, however, this appears to be the first study over the same catalyst of methanol decomposition and methanol–steam reforming. XPS analysis of used catalyst samples and time on-stream data showed that the Cu 2+ oxidation state of copper favors methanol decomposition, and we propose that the deactivation of the catalyst is mainly caused by the change in the oxidation state of copper. 相似文献
12.
A series of sulphated ZrO 2–TiO 2 mixed oxide with different nominal sulphate loadings in the range of 2–15 wt.% was prepared and characterized for their structural properties, surface acidity and benzene isopropylation activity. The catalyst with 10 wt.% nominal sulphate loading showed highest surface area and uniform pore size distributions. Surface acidity, measured by NH 3–TPD method, showed increase in acidity with sulphate loading and the 10 wt.% sulphate loaded catalyst showed highest acidity. The activities of these catalysts were tested for isopropylation of benzene to cumene using 2-propanol as the alkylating agent. The 10 wt.% sulphate-loaded catalyst also showed highest activity for this reaction with 97% cumene selectivity. The higher activity of this catalyst was attributed to its higher acidity. 相似文献
13.
Surface-phase ZrO 2 on SiO 2 (SZrOs) and surface-phase La 2O 3 on Al 2O 3 (SLaOs) were prepared with various loadings of ZrO 2 and La 2O 3, characterized and used as supports for preparing Pt/SZrOs and Pt/SLaOs catalysts. CH 4/CO 2 reforming over the Pt/SZrOs and Pt/SLaOs catalysts was examined and compared with Pt/Al 2O 3 and Pt/SiO 2 catalysts. CO 2 or CH 4 pulse reaction/adsorption analysis was employed to elucidate the effects of these surface-phase oxides. The zirconia can be homogeneously dispersed on SiO2 to form a stable surface-phase oxide. The lanthana cannot be spread well on Al2O3, but it forms a stable amorphous oxide with Al2O3. The Pt/SZrOs and Pt/SLaOs catalysts showed higher steady activity than did Pt/SiO2 and Pt/Al2O3 by a factor of three to four. The Pt/SZrOs and Pt/SLaOs catalysts were also much more stable than the Pt/SiO2 and Pt/Al2O3 catalysts for long stream time and for reforming temperatures above 700 °C. These findings were attributed to the activation of CO2 adsorbed on the basic sites of SZrOs and SLaOs. 相似文献
14.
The reduction of nitrogen monoxide by propene on V 2O 5/ZrO 2 doped with or without calcium has been studied by FTIR spectroscopy as well as by analysis of the reaction products. Considerable promoting effect of calcium doping on the reduction of nitrogen monoxide by propene was observed on the V 2O 5/ZrO 2 catalysts. For the reaction of a mixture of NO+C 3H 6, carbonyl and carboxylate species were observed above 373 K, although nitrate species formed at room temperature on V 2O 5/ZrO 2 doped with calcium. No bands due to a compound including both carbon and nitrogen atoms were observed. Thus, the redox mechanism, i.e. propene reduces the catalyst and nitrogen monoxide oxidizes the catalyst, is confirmed on V 2O 5/ZrO 2 catalysts doped with or without calcium. The analysis of the V=O band in the region of 1100–900 cm −1 indicates that this promotion is mainly due to new V=O species formed by the addition of calcium onto the catalyst. This species is easily reproduced in comparison with the other V=O species on the surface in the reoxidation process of the catalyst. 相似文献
15.
Zirconia supported on alumina was prepared and characterized by BET surface area, X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), temperature programmed desorption (TPD), and pulse reaction. 0.2% Pd/ZrO 2/Al 2O 3 catalyst were prepared by incipient wetness impregnation of supports with aqueous solution of Pd(NO 3) 2. The effects of support properties on catalytic activity for methane combustion and CO oxidation were investigated. The results show that ZrO 2 is highly dispersed on the surface of Al 2O 3 up to 10 wt.% ZrO 2, beyond this value tetragonal ZrO 2 is formed. The presence of a small amount of ZrO 2 can increase the surface area, pore volume and acidity of support. CO–TPD results show that the increase of CO adsorption capacity and the activation of CO bond after the presence of ZrO 2 lead to the increase of catalytic activity of Pd catalyst for CO oxidation. CO pulse reaction results indicate that the lattice oxygen of support can be activated at lower temperature following the presence of ZrO 2, but it does not accelerate the activity of 0.2% Pd/ZrO 2/Al 2O 3 for methane combustion. 0.2% Pd/ZrO 2/Al 2O 3 dried at 120 °C shows highest activity for CH 4 combustion, and the activity can be further enhanced following the repeat run. The increase of treatment temperature and pre-reduction can decrease the activity of catalyst for CH 4 combustion. 相似文献
16.
A series of CuO/ZnO/Al_2O_3, CuO/ZnO/ZrO_2/Al_2O_3 and CuO/ZnO/CeO_2/Al_2O_3 catalysts were prepared by coprecipitation and characterized by N_2 adsorption, XRD, TPR, N_2O titration and HRTEM. The catalytic performances of these catalysts for the steam reforming of methanol were evaluated in a laboratory-scale fixed-bed reactor at 0.1 MPa and temperatures between 473 and 543 K. The results showed that the catalytic activity depended greatly on the catalyst reducibility and the specific surface area of Cu. An approximate linear correlation between the catalytic activity and the Cu surface area was found for all catalysts investigated in this study.Compared to CuO/ZnO/Al_2O_3, the ZrO_2-doped CuO/ZnO/Al_2O_3 exhibited higher activity and selectivity to CO,while the CeO_2-doped catalyst displayed lower activity and selectivity. Finally, an intrinsic kinetic study was carried out over a screened CuO/ZnO/CeO_2/Al_2O_3 catalyst in the absence of internal and external mass transfer effects. A good agreement was observed between the model-derived effluent concentrations of CO(CO_2) and the experimental data. The activation energies for the reactions of methanol-steam reforming, water-gas shift and methanol decomposition over CuO/ZnO/CeO_2/Al_2O_3 were 93.1, 85.1 and 116.5 k J·mol~(-1), respectively. 相似文献
17.
This study reports new gallium-promoted copper-based catalysts prepared by co-impregnation of methoxide–acetylacetonate (acac) precursors from methanolic solutions onto silica and zinc oxide supports. Catalyst performance in the CO 2 hydrogenation to methanol was investigated at 2 MPa and temperatures between 523 and 543 K. A high activity and selectivity for ZnO-supported catalysts was found, which also showed a high stability in terms of both activity and selectivity. The maximum value for the activity was 378 g MeOH/kg cat h at 543 K, with a selectivity of 88% towards methanol production. The high performance of these materials in the CO 2 hydrogenation is related to the presence of Ga 2O 3 promoter and highly dispersed Cu + species on the surface, determined by XPS and Auger on used catalysts. 相似文献
18.
ZrO 2–TiO 2 mixed oxides, prepared using the sol–gel method, were used as supports for platinum catalysts. The effects of catalyst pre-reduction and surface acidity on the performance of Pt/ZT catalysts for the reduction of NO with CH 4 were studied. The diffuse reflectance infrared Fourier transformed (DRIFT) spectra of CO adsorbed on the Pt/ZT catalysts, and also on the Pt/T and Pt/Z references, pre-reduced at 773 K in hydrogen, revealed that an SMSI state is developed in the Ti-rich oxide-supported platinum catalysts. However, no shift in the binding energy of Pt 4f 7/2 level for Pt/T and Pt deposited on Ti-rich support counterparts pre-reduced at 773 K was found by photoelectron spectroscopy. The DRIFT spectra of the catalysts under the NO+O 2 co-adsorption revealed the appearance of nitrite/nitrate species on the surface of the Zr-containing catalysts, which displayed acidic properties, but were almost absent in the Pt/T catalyst. The intensity of these bands reached a maximum for the Pt/ZT(1:1) catalyst, which in turn exhibited a larger specific area. In the absence of oxygen in the feed stream, the NO+CH 4 reaction showed DRIFT spectra assigned to surface isocyano species. Since the intensity of this band is higher for the Pt/ZT (9:1) catalyst, it seems that such species are developed at the Pt–support interface. 相似文献
19.
Catalytic activity of ZrO 2 supported PdO catalysts for methane combustion has been investigated in comparison with Al 2O 3 supported PdO catalysts. It was found that the drop of catalytic activity owing to decomposition of PdO at a high temperature region (600–900°C) was suppressed by using ZrO 2 support. Temperature-programmed reduction (TPR) measurements of the catalyst with hydrogen revealed that the PdO of PdO/Al 2O 3 catalyst was reduced at the temperature less than 100°C, whereas in PdO/ZrO 2 catalyst the consumption of hydrogen was also observed at 200–300°C. This result indicates that the stable PdO species were present in the PdO/ZrO 2 catalyst. In order to confirm the formation of the solid solution of PdO and ZrO 2, X-ray diffraction (XRD) analyses of the mixtures of ZrO 2 and PdO calcined at 700–900°C in air were carried out. The lattice volume of ZrO 2 in the mixture was larger than that of ZrO 2. Furthermore, the Pd thin film on ZrO 2 substrate was prepared as a model catalyst and the depth profile of the elements in the Pd thin film was measured by Auger electron spectroscopy (AES). It was confirmed that Zr and O as well as Pd were present in the Pd thin film heated at 900°C in air. It was considered that the PdO on ZrO 2 support might be stabilized by the formation of the solid solution of PdO and ZrO 2. 相似文献
20.
The effects of ZrO 2 content on the CO oxidation activity in a series of CuO x/Ce xZr 1−xO 2 ( x = 0, 0.15, 0.5, 0.7 and 1) catalysts were investigated, both in the absence and in the presence of H 2, i.e. preferential CO oxidation—PROX. The investigation was performed under light-off conditions to focus the effects of transients and shut-down/start-up cycles on the performance; such phenomena are expected to affect the activity of PROX catalysts in small/delocalised fuel reformers. Evidence has been obtained for a transition from an “oxidized” towards a “reduced” state of the catalyst under the simulated PROX reaction conditions as a function of the reaction temperature, leading to different active species under the reaction conditions. Both CO oxidation activity and PROX selectivity appear to be affected by this process. IR characterisation of the surface copper species suggests an important role of reduced cerium sites in close contact with copper clusters on the CO oxidation activity at low temperatures. 相似文献
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