共查询到20条相似文献,搜索用时 15 毫秒
1.
Chang Ryul Jung Arunabha Kundu Suk Woo Nam Ho-In Lee 《Applied catalysis. B, Environmental》2008,84(3-4):426-432
Copper oxide–ceria (CuO–CeO2) catalyst for selective oxidation of carbon monoxide (CO) was prepared by co-precipitation and hydrothermal treatment methods and evaluated for catalytic activity in a reformate gas composition which simulated the produced gas from methanol steam reforming. By applying the condition of hydrothermal treatment, the catalytic activity of CuO–CeO2 catalyst was increased and the operating temperature window, in which the concentration of carbon monoxide was lower than 10 ppm, was widened. From the thermogravimetric (TG) results of hydrothermally treated catalyst precursor, CuO–CeO2 catalyst did not show any improvement in physical properties such as Brunauer Emmett Teller (BET) surface area, pore volume and average pore diameter, but the chemical stability might be enhanced by hydrothermal treatment. By hydrothermal treatment, cuprous ion in the CuO–CeO2 catalyst migrated to the surface of catalyst resulting in increased surface concentration of copper and formation of cupric oxide on the surface of catalyst during calcination. While increasing the calcination temperature (i.e. above 800 °C), the phase separation occurred with a part of copper and cupric oxide was formed on the surface of catalyst which was observed in X-ray diffraction (XRD) analysis. 相似文献
2.
Benjaram M. Reddy Seung-Cheol Lee Dae-Soo Han Sang-Eon Park 《Applied catalysis. B, Environmental》2009,87(3-4):230-238
Vanadium oxide and cerium oxide doped titania–zirconia mixed oxides were explored for oxidative dehydrogenation of ethylbenzene to styrene utilizing carbon dioxide as a soft oxidant. The investigated TiO2–ZrO2 mixed oxide support with high specific surface area (207 m2 g−1) was synthesized by a coprecipitation method. Over the calcined support (550 °C), a monolayer equivalent (15 wt.%) of V2O5, CeO2 or a combination of both were deposited by using wet-impregnation or co-impregnation methods to make the V2O5/TiO2–ZrO2, CeO2/TiO2–ZrO2 and V2O5–CeO2/TiO2–ZrO2 combination catalysts, respectively. These catalysts were characterized using X-ray diffraction (XRD), Raman, scanning electron microscopy (SEM), transmission electron microscopy (TEM), temperature preprogrammed reduction (TPR), CO2 temperature preprogrammed desorption (TPD) and BET surface area methods. All characterization studies revealed that the deposited promoter oxides are in a highly dispersed form over the support, and the combined acid–base and redox properties of the catalysts play a major role in this reaction. The V2O5–CeO2/TiO2–ZrO2 catalyst exhibited a better conversion and product selectivity than other combinations. In particular, the addition of CeO2 to V2O5/TiO2–ZrO2 prevented catalyst deactivation and helped to maintain a high and stable catalytic activity. 相似文献
3.
A series of MnOx–CeO2 mixed oxide catalysts with different compositions prepared by sol–gel method were tested for the catalytic combustion of chlorobenzene (CB), as a model of volatile organic compounds of chlorinated aromatics. MnOx–CeO2 catalysts with different ratios of Mn/Ce + Mn were found to possess high catalytic activity in the catalytic combustion of CB, and MnOx(0.86)–CeO2 was identified as the most active catalyst, on which the temperature of complete combustion of CB was 254 °C. Effects of systematic variation of reaction conditions, including space velocity and inlet CB concentration on the catalytic combustion of CB were investigated. Additionally, the stability and deactivation of MnOx–CeO2 catalysts were studied by various characterization methods and other assistant experiments. MnOx–CeO2 catalysts with high Mn/Ce + Mn ratios present a stable high activity, which is related to their high ability to remove the adsorbed Cl species and a large amount of active surface oxygen. 相似文献
4.
CeO2–TiO2 (Ce:Ti = 0.25–9, molar ratio) catalysts were synthesized by a sol–gel method and the catalytic performances were evaluated in the selective synthesis of isobutene and isobutane from CO hydrogenation under the reaction conditions of 673–748 K, 1–5 MPa and 720–3000 h−1. The physical properties, such as specific surface area, cumulative pore volume, average pore diameter, crystal phase and size, of the catalysts were characterized by N2 adsorption/desorption and XRD. All the CeO2–TiO2 composite oxides showed higher surface areas than pure TiO2 and CeO2. No TiO2 phase was detected on the samples of CeO2–TiO2 in which TiO2 contents were in the range of 10–50 mol%. Crystalline Ce2O3 was detected in CeO2–TiO2 (8:2). The reaction conditions, temperature, pressure and space velocity, had obvious influences on the CO conversion and distribution of the products over CeO2–TiO2 (8:2) catalyst. 相似文献
5.
The roles of cationic and nonionic Au species in the water–gas shift (WGS) reaction on Au/CeO2 catalysts were studied by comparing the reaction behavior of a cyanide leached catalyst, after removal of the Au nanoparticles by cyanide leaching, with that of non-leached catalysts, following the technique introduced by Q. Fu et al. [Science 301 (2003) 935]. Using rate measurements as well as in situ spectroscopic and structure-sensitive techniques, we found that based on the Au mass balance, cyanide leaching removed all Au except for ionic Au3+ species, and that leaching resulted in a pronounced decay of the catalyst mass normalized activity to 1–25% of that of a non-leached catalyst. The extent of the activity loss strongly depended on the post-treatment of the leached catalyst. Both the catalyst treatment after leaching and, in particular, the WGS reaction resulted in considerable reformation of Au0 species by thermal decomposition of Au oxides (Au3+) and subsequent nucleation and growth of very small Au0 aggregates and metallic Au0 nanoparticles, as indicated by Au(4f) signals at 85.9 eV (Au3+), 84.0–84.6 eV (up-shifted signal of small Au0 aggregates), and 84.0 eV (metallic Au0). In this work, correlations between ionic and nonionic Au species and between total WGS activity and activity for the formation/decomposition of bidentate formate species are evaluated, and the role of the respective Au species in the WGS reaction on Au/CeO2 catalysts is discussed. 相似文献
6.
CuO–CeO2 is prepared by coprecipitation and ethanol washing and characterized using BET, HR-TEM, XRD and TPR techniques. The results show that CuO–CeO2 is nanosized (rTEM = 6.5 nm) and possesses high surface area (SBET = 138 m2 g−1). Furthermore, some lattice defects in the surface of CuO–CeO2 are found, which are beneficial to enhance catalytic performance of CuO–CeO2 in preferential oxidation of CO in excess hydrogen (PROX). Consequently, the nanostructured CuO–CeO2 exhibits perfect catalytic performance in PROX. Namely, CO content can be lowered to less than 100 ppm at 150 °C with 100% selectivity of O2 in the presence of 8% CO2 and 20% H2O at . 相似文献
7.
MnOx–CeO2 mixed oxide catalysts prepared by sol–gel method were tested for the catalytic combustion of chlorobenzene (CB), as a model of chlorinated aromatic volatile organic compounds (CVOCs). MnOx–CeO2 catalysts with the different ratio of Mn/Ce + Mn were found to possess high catalytic activity for catalytic combustion of CB, and MnOx(0.86)–CeO2 was the most active catalyst, on which the complete combustion temperature (T90%) of chlorobenzene was 236 °C. The stability of MnOx–CeO2 catalysts in the CB combustion was investigated. MnOx–CeO2 catalysts with high Mn/Ce + Mn ratios present high stable activity, which is related to their high ability to remove Cl species adsorbed and a large amount of active surface oxygen. 相似文献
8.
Jong Wook Bae Suk-Hwan Kang Yun-Jo Lee Ki-Won Jun 《Applied catalysis. B, Environmental》2009,90(3-4):426-435
The catalytic activity on the coprecipitated Cu–ZnO–Al2O3/Zr-ferrierite (CZA–ZrFER) with different Zr content from 0 to 5 wt.% was investigated for the direct synthesis of dimethylether (DME) from H2-deficient and biomass-derived model syngas (H2/CO molar ratio = 0.93). The catalytic functionalities, such as CO conversion and DME selectivity, showed their maxima on the bifunctional catalyst with 3 wt.% Zr-modified ferrierite. Detailed characterization studies were conducted on the catalysts to measure their properties such as surface area, acidity by temperature-programmed desorption of ammonia (NH3-TPD), reducibility of Cu oxide by temperature-programmed reduction (TPR), copper surface area measurements by N2O titration method, electronic states of copper by IR analysis and particle size measurement by XRD and TEM analysis. The number of acid sites measured by NH3-TPD on the bifunctional catalysts decreased monotonously with the increase of Zr content, meanwhile, the acidic strength is found to be minimal on the catalyst showing best performance. The reducibility of copper oxide and the surface area of metallic copper also exhibited their maximum values at the same Zr composition indicating that these are responsible for the optimum functionality of the bifunctional CZA–ZrFER catalyst. The role of easily reducible copper species with small particle size and the suppressed strong acidic sites is also emphasized in the consecutive reaction from syngas to DME on the bifunctional catalyst. The different behavior of intrinsic rate of the bifunctional catalysts is also well correlated with the metallic surface area of copper and the amount of acidic sites with their acidic strength. 相似文献
9.
Huifang Wang Yixin Lian Yinong Li Weiping Fang Yiquan Yang 《Catalysis communications》2009,10(14):1864-1867
The effects of incorporating tungsten into the traditional Co–Mo–K/γ–Al2O3 catalysts on the catalytic performances for water–gas shift reaction were investigated. Activity tests showed that W-promoted Co–Mo–K/γ–Al2O3 catalysts exhibited higher activity than W-free Co–Mo–K/γ–Al2O3 catalyst. Raman and H2-TPR studies indicated that part of the octahedrally coordinated Mo–O species on Co–Mo–K catalysts transformed into tetrahedrally coordinated Mo–O species in the presence of W promoter. 相似文献
10.
A series of samples of La–Cr–O– perovskites were designed as catalysts for diesel soot combustion. They were prepared by using co-precipitation method, at ambient temperature using ammonia followed by a hydrothermal treatment (T = 200 °C, P = 20 atm, t = 24 h). All the chromium-containing precursors were then calcined at high temperature to develop the oxide catalyst. Two phase composition 86%LaCrO3–(14%) La2CrO6 or 94%LaCrO3–6%La2O3 were formed depending on the atmosphere of calcination (oxygen or hydrogen respectively) used. Their respective BET surface areas were 1.1 and 6.5 m2 g−1. Highly crystalline, pure phase of LaCrO3 and La2CrO6 powders were also prepared, with BET area of 4 and 3 m2 g−1, respectively. The crystalline structure and properties of all samples were characterised by X-ray diffraction (XRD), using Rietveld refinement, and temperature-programmed reduction (TPR) techniques. O2-TPD measurements performed on all samples showed the presence of suprafacial, weakly chemisorbed oxygen only for LaCrO3, which contributes actively to soot combustion. TPR study performed on all catalysts showed that while pure LaCrO3 and La2O3 samples did not reduce, the biphasic catalysts showed the presence of oxygen depletion peaks characteristic of lattice oxygen mobility in the samples at ca. 665 °C. Catalytic combustion of diesel soot was studied over all catalysts. The results showed that pure LaCrO3 exhibited significant catalytic activity which was sensitively affected by the modifier La2CrO6 or La2O3. 相似文献
11.
Jianlin Li Heesung Yoon Tak-Keun Oh Eric D. Wachsman 《Applied catalysis. B, Environmental》2009,92(3-4):234-239
The water–gas shift (WGS) reaction is used to shift the CO/H2 ratio prior to Fischer–Tropsch synthesis and/or to increase H2 yield. A WGS membrane reactor was developed using a mixed protonic–electronic conducting SrCe0.9Eu0.1O3−δ membrane coated on a Ni–SrCeO3−δ support. The membrane reactor overcomes the thermodynamic equilibrium limitations. A 46% increase in CO conversion and total H2 yield was achieved at 900 °C under 3% CO and 6% H2O, resulting in a 92% single pass H2 production yield and 32% single pass yield of pure permeated H2. 相似文献
12.
Khampol Sirichaiprasert Sangobtip Pongstabodee Apanee Luengnaruemitchai 《Journal of the Chinese Institute of Chemical Engineers》2008,39(6):597-607
Single- and double-stage catalytic preferential CO oxidation (CO-PrOx) over-Fe2O3-promoted CuO–CeO2 in a H2-rich stream has been investigated in this work. The catalyst was prepared by the urea-nitrate combustion method and was characterized by X-ray diffractometer (XRD), X-ray fluorescence (XRF), Brunauer–Emmet–Teller (BET), transmission electron microscope (TEM), and scanning electron microscope (SEM). The catalytic activity tests were carried out in the temperature range of 50–225 °C under atmospheric pressure. The results of the single-stage reaction indicated that complete CO oxidation was obtained when operating at a O2/CO ratio of 1.5, W/F ratio of 0.36 g s/cm3, and at a reaction temperature of 175 °C. At these conditions, H2 consumption in the oxidation was estimated at 58.4%. Applying the same conditions to the double-stage reaction, complete CO oxidation was found and H2 consumption in the oxidation was reduced about 4.9%. When decreasing the double-stage reaction temperature to 150 °C, the results elucidated that CO could be converted to CO2 completely while H2 consumption in the oxidation was further reduced to 33.5%. A temperature blocking 22 factorial design has been used to describe the importance of the factors influencing the catalytic activity. The factorial design was according to the experimental results. When adding CO2 and H2O in feed, reduction of CO conversion for single- and double-stage reaction is obtained due to a blocking of CO2 and H2O at a catalytic active site. Comparing CO conversion obtained when operating with/without CO2 and H2O in feed for single- and double-stage reaction, less reduction is achieved when operating in double-stage reaction. 相似文献
13.
Dongzhi Zhang Hengbo Yin Chen Ge Jinjuan Xue Tingshun Jiang Longbao Yu Yutang Shen 《Journal of Industrial and Engineering Chemistry》2009,15(4):537-543
A series of Cu–Zn–Zr catalysts were prepared by a coprecipitation method and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, temperature programmed reduction, and N2 adsorption. The catalytic activity of the Cu–Zn–Zr catalyst in the hydrogenation of maleic anhydride using ethanol as a solvent was studied at 220–280 °C and 1 MPa. Maleic anhydride was mainly hydrogenated to γ-butyrolactone and tetrahydrofuran while ethanol dehydrogenated to ethyl acetate. After reduction, CuO species present in the calcined Cu–Zn–Zr catalysts were converted to metallic copper (Cu0). The presence of ZrO2 favored the deep hydrogenation of γ-butyrolactone to tetrahydrofuran while the presence of ZnO was beneficial to the formation of the intermediate product γ-butyrolactone. The molar ratios of the hydrogen produced in ethanol dehydrogenation to the hydrogen consumed in maleic anhydride hydrogenation increased with the increase of the reaction temperature. 相似文献
14.
Yafen Zhou Haiyan Fu Xiaojuan Zheng Ruixiang Li Hua Chen Xianjun Li 《Catalysis communications》2009,11(2):137-141
A ruthenium–platinum bimetallic catalyst supported on boehmite was prepared by co-impregnation and hydrothermal reduction and characterized by XRD, TEM and TG–DTG. Reduction time of the catalyst affected the conversion of γ-Al2O3 to boehmite and the specific surface area of the catalyst, and consequently influenced the catalytic performance of the catalyst. Under the same conditions, the Ru–Pt/AlOOH catalyst showed much higher activity and selectivity than the Ru–Pt/γ-Al2O3 in aqueous hydrogenation of methyl propionate. The selectivity to 1-propanol of 97.8% could be obtained at methyl propionate conversion of 89.1% over Ru–Pt/AlOOH at 453 K under 5 MPa of H2 for 6 h. It is postulated that the high performance of this novel catalyst is related to the cooperation of the hydroxyl groups of support surface and water solvent. 相似文献
15.
Kazufumi Nishida Dalin Li Yingying Zhan Tetsuya Shishido Yasunori Oumi Tsuneji Sano Katsuomi Takehira 《Applied Clay Science》2009,44(3-4):211-217
Trace amounts of MgO were doped on Cu/ZnO/Al2O3 catalysts with the Cu/Zn/Al molar ratio of 45/45/10 and tested for the water–gas shift (WGS) reaction. A mixture of Zn(Cu)–Al hydrotalcite (HT) and Cu/Zn aurichalcite was prepared by co-precipitation (cp) of the metal nitrates and calcined at 300 °C to form the catalyst precursor. When the precursor was dispersed in an aqueous solution of Mg(II) nitrate, HT was reconstituted by the “memory effect.” During this procedure, the catalyst particle surface was modified by MgO-doping, leading to a high sustainability. Contrarily, cp-Mg/Cu/Zn/Al prepared by Mg2+, Cu2+, Zn2+ and Al3+ co-precipitation as a control exhibited high activity but low sustainability. Mg2+ ions were enriched in the surface layer of m-Mg–Cu/Zn/Al, whereas Mg2+ ions were homogeneously distributed throughout the particles of cp-Mg/Cu/Zn/Al. CuO particles were significantly sintered on the m-catalyst during the dispersion, whereas CuO particles were highly dispersed on the cp-catalyst. However, the m-catalyst was more sustainable against sintering than the cp-catalyst. Judging from TOF, the surface doping of MgO more efficiently enhanced an intrinsic activity of the m-catalyst than the cp-catalyst. Trace amounts of MgO on the catalyst surface were enough to enhance both activity and sustainability of the m-catalyst by accelerating the reduction–oxidation between Cu0 and Cu+ and by suppressing Cu0 (or Cu+) oxidation to Cu2+. 相似文献
16.
The MOx–CeO2/CuO (M = Co, Mn, Sn and Zn) catalysts were synthesized by the hydrothermal method and characterized by XRD, BET, SEM, H2-TPR and HRTEM techniques. It is found that the MnO2–CeO2/CuO catalyst exhibits the best activity from 75 °C to 115 °C, suggesting that the addition of Mn is the most effective for improving low-temperature activity. The reasons are that MnO2 improves the dispersion of CeO2 and the textural property of CeO2/CuO catalyst. Moreover, the presence of MnO2 is favorable for preventing the reduction of CuO, and MnO2 also enhances the interaction between CeO2 and CuO. 相似文献
17.
P. Yaseneva S. Pavlova V. Sadykov E. Moroz E. Burgina L. Dovlitova V. Rogov S. Badmaev S. Belochapkin J. Ross 《Catalysis Today》2008,138(3-4):175
Active and selective Cux(CeZrY)1−xOy catalysts (pure and with addition of Al2O3 and Cr) for the steam reforming of methanol were synthesized via the urea–nitrate combustion method. Structural, surface and redox characteristics of these catalysts were investigated by XRD, BET, IR spectroscopy, differential dissolution (DD), H2-TPR and XPS methods. It was shown that addition of alumina and Cr leads to the steep increase in H2 production due to appearance of highly dispersed copper species and stabilizes their activity. The parallel change of SRM rate constants and maximal rates of reduction with hydrogen characterizing mobility of lattice oxygen at variation of the catalyst composition was revealed that shows the importance of lattice oxygen mobility for steam reforming of methanol. 相似文献
18.
Keita Watanabe Toshihiro Miyao Kazutoshi Higashiyama Hisao Yamashita Masahiro Watanabe 《Catalysis communications》2009,10(14):1952-1955
The effect of Fe content in Ni–Fe–Al oxide nano-composites prepared by the solution-spray plasma technique on their catalytic activity for the high temperature water–gas shift reaction was investigated. The composites showed a hollow sphere structure, with highly dispersed Fe–Ni particles supported on the outer surface of the spheres. When the water–gas shift reaction was performed over an Ni–Al oxide composite catalyst without Fe, undesired CO methanation took place predominantly compared to the water–gas shift reaction, and significant amounts of hydrogen were consumed. When appropriate amounts of Fe were added to the Ni–Al oxide composite catalyst during the plasma process, methanation was suppressed remarkably, without serious loss of activity for the water–gas shift reaction. The catalyst was characterized by STEM, XRD and H2 chemisorption measurements. 相似文献
19.
The rate of Fischer–Tropsch synthesis over an industrial well-characterized Co–Ru/γ-Al2O3 catalyst was studied in a laboratory well mixed, continuous flow, slurry reactor under the conditions relevant to industrial operations as follows: temperature of 200–240 °C, pressure of 20–35 bar, H2/CO feed ratio of 1.0–2.5, gas hourly space velocity of 500–1500 N cm3 gcat− 1 h− 1 and conversions of 10–84% of carbon monoxide and 13–89% of hydrogen. The ranges of partial pressures of CO and H2 have been chosen as 5–15 and 10–25 bar respectively. Five kinetic models are considered: one empirical power law model and four variations of the Langmuir–Hinshelwood–Hougen–Watson representation. All models considered incorporate a strong inhibition due to CO adsorption. The data of this study are fitted fairly well by a simple LHHW form − RH2 + CO = apH20.988pCO0.508 / (1 + bpCO0.508)2 in comparison to fits of the same data by several other representative LHHW rate forms proposed in other works. The apparent activation energy was 94–103 kJ/mol. Kinetic parameters are determined using the genetic algorithm approach (GA), followed by the Levenberg–Marquardt (LM) method to make refined optimization, and are validated by means of statistical analysis. Also, the performance of the catalyst for Fischer–Tropsch synthesis and the hydrocarbon product distributions were investigated under different reaction conditions. 相似文献
20.
Marta Boaro Michela Vicario Jordi Llorca Carla de Leitenburg Giuliano Dolcetti Alessandro Trovarelli 《Applied catalysis. B, Environmental》2009,88(3-4):272-282
In this study platinum- and gold-based catalysts supported on ZrO2 and ceria–zirconia solid solution have been characterized by several techniques (TPR, XRD, BET, HRTEM) and tested in the water gas shift (WGS) reaction under feed conditions typical of an autothermal reformer outlet. Platinum and gold catalysts behave differently especially in the range of 423–513 K, with gold being superior than platinum. The possibility of modifying the redox and structural characteristics of zirconia with the insertion of ceria allowed us to conclude that the bulk redox properties of the support play a secondary role, while the key parameter for an active WGS catalyst is the nature of metal support interface. This, in turn, depends on the metal particle distribution and on the structural and morphological properties of support. It has been found that the synergism between precious metals and support can be designed with an appropriate choice of the parameters of synthesis and the characteristics of support. 相似文献