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1.
We prepared Pt catalysts supported on various metal oxides, viz., ZrO2, CeO2, TiO2, yttria-stabilized zirconia (YSZ), SiO2, SiO2–Al2O3, and γ-Al2O3, using an incipient wetness method and applied them to propane combustion. In the cases of ZrO2-, CeO2-, and TiO2-supported Pt catalysts, supports with different surface areas were also used. The Pt dispersion in Pt catalysts supported on metal oxides increased with increasing surface area of the support for the same metal oxide. Pt catalysts on supports with lower surface areas (ZrO2, CeO2, and TiO2) showed higher catalytic activities for propane combustion than did Pt catalysts on supports with higher surface areas. The catalytic activity decreased in the following order: Pt/ZrO2 (2) > Pt/CeO2 (9) > Pt/TiO2 (1) = Pt/SiO2 (350) > Pt/ZrO2 (18) = Pt/YSZ > Pt/TiO2 (330) > Pt/SiO2–Al2O3 (350) > Pt/ZrO2 (73) > Pt/γ-Al2O3 (180) > Pt/CeO2 (160). The catalytic activity is inversely proportional to the amount of O2 chemisorbed up to the reaction temperature. It can be concluded that metallic Pt is essential for propane combustion and is maintained for the Pt catalysts with large Pt metal particles, which can be prepared by using a support with a low surface area.  相似文献   

2.
СоМоS/Sup catalysts were prepared from 12-molybdophosphoric heteropoly acid and cobalt citrate, with Al2O3, SiO2, TiO2, and ZrO2 used as supports (Sup). The synthesized catalysts were studied by low-temperature nitrogen adsorption, X-ray diffraction, temperature-programmed ammonia desorption, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. The catalytic properties of the catalysts were studied in a flow-through installation at 260 and 340°С, pressure of 3.0 MPa, feed space velocity of 80 h–1, and Н2/feed ratio of 500 Ln.c. L–1. The guaiacol hydrodeoxygenation rate increases with a decrease in the mean length of the active phase particles, irrespective of the kind of the oxide support. As for the support effect, the catalyst activity decreases in the order SiO2 > Al2O3 > ZrO2 ~ TiO2. On the other hand, the catalysts supported on ZrO2 and Al2O3 exhibit the highest stability. The causes of the observed trends and the possible relationships between the characteristics of the catalysts and active phase nanoparticles are discussed.  相似文献   

3.
The solid acids such as ZrO2, Al2O3 and ZrO2-Al2O3 containing different ZrO2 loadings (10–80 mol%) were prepared by solution combustion method (SCM) and characterized for their total surface acidity by NH3-TPD/n-butylamine back titration method and crystallinity by powder X-ray diffraction (PXRD) technique. These solid acids were evaluated for their catalytic activity in the synthesis of novel O-acetylated products from substituted phenols, pyridine alcohols and aryl alcohols with acetic anhydride (AA) as an acetylating agent. The reaction conditions were optimized by varying the catalyst, molar ratio of the reactants, reaction temperature and amount of the catalyst. All the solid acids used in this study exhibited good catalytic activity in the reaction. In particular, ZrO2-Al2O3 containing 80 mol% of ZrO2 was found to be highly active in the acetylation reaction with high yield of acetylated products. Triangular correlation between the surface acidity, crystallinity and catalytic activity of solid acids was observed. These solid acids were found to be reactivable and reusable.  相似文献   

4.
The structure, texture, and acid properties of platinum catalysts on oxide (Al2O3, ZrO2, ZrO2–Al2O3) and borate-containing supports (B2O3–Al2O3, B2O3–ZrO2) are studied. The catalysts are tested in the process of hydrocracking sunflower-seed oil at 380°C, 4.0 MPa, and a weight stock feed rate of 1.0 h–1. It has been found that aluminum oxide (A) contains the γ-Al2O3 phase, zirconium dioxide (Z) includes 85 and 15 rel. % of the monoclinic (M) and tetragonal (T) phases, respectively, while zirconium dioxide with the addition of 2.5 wt % Al2O3 (ZA) comprises 14 and 86 rel. % of the M–ZrO2 and T–ZrO2 phases, respectively. The B2O3–Al2O3 (BA) and B2O3–ZrO2 (BZ) systems modified with boron oxide (20 wt %) are X-ray amorphous. A Pt/BA catalyst differs from a Pt/A catalyst, while a Pt/BZ catalyst has a larger specific surface area and acidity than Pt/Z and Pt/ZA catalysts and contains Bronsted acidic centers (BACs) along with Lewis acidic centers (LACs). Only LACs are present on the surface of Pt/A, Pt/Z, and Pt/ZA catalysts. The LAC/BAC ratio in Pt/BA and Pt/BZ catalysts is 0.3 and 1.0, respectively. All the catalysts provide complete oil conversion to give C5+ hydrocarbons with a yield of 81.7–87.3 wt %. Pt/A catalyzes mainly decarboxylation and hydrogenation–dehydration reactions, while Pt/Z and Pt/ZA provide decarboxylation. The yield of diesel fraction reaches 71.8–73.9 wt % with an n-alkane content of 94.0–95.9 wt %. One-stage oil hydrocracking with the prevalence of hydrodecarbonylation and hydrogenation–dehydration reactions occurs on Pt/BA and Pt/BZ catalysts for 20 h to give the yield of the diesel fraction of at least 81.4 and 74.4 wt % and the total content of iso-alkanes and cycloalkanes of at least 28.3 and 60.7 wt %, respectively.  相似文献   

5.
Solid-acid catalytic materials such as ZrO2-Al2O3 containing 80?mol% of ZrO2 were prepared by the solution combustion method (SCM) using different fuels such as urea, hexamethylene tetramine, glycine, and sucrose. All the prepared solid acid catalytic materials were characterized for their physico-chemical properties like crystalinity, acidity, functionality and morphology. These materials were evaluated for their catalytic activity in the synthesis of a series of novel substituted benzimidazoles. The reaction conditions were optimized by varying the solvents, reaction temperature, weight of solid acid catalyst, molar ratio of the reactants, and reaction time. The ZrO2-Al2O3 solid acid catalytic material prepared by urea as a fuel was found to be highly active, recyclable, and reusable in the synthesis of benzimidazoles. A possible reaction mechanism for the synthesis of benzimidazoles is also proposed.  相似文献   

6.
The catalytic activity of the CuO/ZrO2, CoO/ZrO2, Fe2O3/ZrO2, and CuO/(CoO, Fe2O3)/ZrO2 systems in the reaction of selective CO oxidation in the presence of hydrogen was studied at 20–450°C over the oxide concentration range of 2.5–10 wt % on the surface of ZrO2. The conversion of CO on the CoO/ZrO2 systems was almost independent of the concentration of CoO: 88 or 90% for 2.5 or 10% CoO, respectively. TPR data allowed us to relate the catalytic activity of CoO/ZrO2 to Co-O-Zr clusters, the amount of which was almost constant over the test range of CoO concentrations. The conversion of CO on 2.5% CuO/ZrO2 was 32% (190°C) or 62–66% on 5–10% CuO/ZrO2 (170°C). According to TPR data, clusters like Cu-O-Zr occurred on the surface of ZrO2, and the amount of these clusters reached a maximum upon supporting 5% CuO. The catalytic properties of 5% CuO/5% CoO/ZrO2 and 5% CoO/5% CuO/ZrO2 samples were identical to those of 5% CuO/ZrO2 samples. It is likely that the formation of active reaction sites upon consecutively supporting the oxides occurred on the same surface sites of ZrO2. In this case, Co and Cu oxides competed for cluster formation, and the copper cation can displace the cobalt cation from the formed clusters. The Fe2O3 samples were inactive; a maximum conversion of 34% (290°C) was observed on 10% Fe2O3/ZrO2. The catalytic properties of CuO/Fe2O3/ZrO2 were also identical to those of CuO/ZrO2, and they depended on the presence of Cu-O-Zr clusters on the surface.  相似文献   

7.
In order to obtain a catalyst support with a high surface area, ZrO2 and ZrO2-Y2O3 were prepared by the hydrolytic decomposition of the corresponding isopropoxide dissolved in benzene. The hydrolysis was carried out at 80°C using an excess amount of distilled water in flowing dry nitrogen. The precipitates thus obtained were dried at 100°C followed by calcination at 500°C in air or nitrogen for 1 h. The specific surface areas for both of the ZrO2 and ZrO2-Y2O3 increased with increasing amount of water added for hydrolysis, and the surface areas for ZrO2-Y2O3 increased with increasing yttrium content. A ZrO2 having a surface area of 130 m2/g was produced, and a stabilized tetragonal ZrO2 with 15 mol% Y3+ having a surface area of 200 m2/g was produced. Furthermore, despite the difference in the ZrO2 and ZrO2-Y2O3 crystal structures, the lattice-strain of ZrO2 has been unequivocally related to the surface area.  相似文献   

8.
The catalytic combustion of particulate material was studied on cobalt catalysts promoted with potassium using different supports for its preparation. Silica, aluminium oxides and hydroxides, zirconium oxide and hydroxide were used as supports. The catalytic activity for combustion depends on the type of support used, the higher activity corresponding to the supported catalyst on zirconium oxide. TPR studies indicate that the interaction metal/support allows to explain the higher activity of the CoK/SiO2 catalyst with respect to the CoK/Al2O3 but the high activity found in CoK/ZrO2is not explained by this interaction. In all cases the Co and K improved the performance of the catalysts.  相似文献   

9.
This review paper reports the recent progress concerning the application of nickel–alumina–zirconia based catalysts to the ethanol steam reforming for hydrogen production. Several series of mesoporous nickel–alumina–zirconia based catalysts were prepared by an epoxide-initiated sol–gel method. The first series comprised Ni–Al2O3–ZrO2 xerogel catalysts with diverse Zr/Al molar ratios. Chemical species maintained a well-dispersed state, while catalyst acidity decreased with increasing Zr/Al molar ratio. An optimal amount of Zr (Zr/Al molar ratio of 0.2) was required to achieve the highest hydrogen yield. In the second series, Ni–Al2O3–ZrO2 xerogel catalysts with different Ni content were examined. Reducibility and nickel surface area of the catalysts could be modulated by changing nickel content. Ni–Al2O3–ZrO2 catalyst with 15 wt% of nickel content showed the highest nickel surface area and the best catalytic performance. In the catalysts where copper was introduced as an additive (Cu–Ni–Al2O3–ZrO2), it was found that nickel dispersion, nickel surface area, and ethanol adsorption capacity were enhanced at an appropriate amount of copper introduction, leading to a promising catalytic activity. Ni–Sr–Al2O3–ZrO2 catalysts prepared by changing drying method were tested as well. Textural properties of Ni–Sr–Al2O3–ZrO2 aerogel catalyst produced from supercritical drying were enhanced when compared to those of xerogel catalyst produced from conventional drying. Nickel dispersion and nickel surface area were higher on Ni–Sr–Al2O3–ZrO2 aerogel catalyst, which led to higher hydrogen yield and catalyst stability over Ni–Sr–Al2O3–ZrO2 aerogel catalyst.  相似文献   

10.
A series of MoO3/ZrO2–Al2O3 catalysts was prepared and investigated in the sulfur-resistant methanation aimed at production of synthetic natural gas. Different methods including impregnation, deposition precipitation, and co-precipitation were used for preparing ZrO2–Al2O3 composite supports. These composite supports and their corresponding Mo-based catalysts were investigated in the sulfur-resistant methanation, and characterized by N2 adsorption–desorption, XRD and H2-TPR. The results indicated that adding ZrO2 promoted MoO3dispersion and decreased the interaction between Mo species and support in the MoO3/ZrO2–Al2O3 catalysts. The co-precipitation method was favorable for obtaining smaller ZrO2 particle size and improving textural properties of support, such as better MoO3 dispersion and increased concentration of Mo6+ species in octahedral coordination to oxygen. It was found that the MoO3/ZrO2–Al2O3 catalyst with ZrO2Al2O3 composite support prepared by co-precipitation method exhibited the best catalytic activity. The ZrO2 content in the ZrO2Al2O3 composite support was further optimized. The MoO3/ZrO2–Al2O3 with 15 wt % ZrO2 loading exhibited the highest sulfur-resistant CO methanation activity, and excess ZrO2 reduced the specific surface area and enhanced the interaction between Mo species and support. The N2 adsorption-desorption results indicated that the presence of ZrO2 in excessive amounts decreased the specific surface area since some amounts of ZrO2 form aggregates on the surface of the support. The XRD and H2-TPR results showed that with the increasing ZrO2 content, ZrO2 particle size increased. These led to the formation of coordinated tetrahedrally Mo6+(T) species and crystalline MoO3, and this development was unfavorable for improving the sulfur-resistant methanation performance of MoO3/ZrO2–Al2O3 catalyst.  相似文献   

11.
Various compositions of the ZrO2/Nb2O5 system were synthesized and the experimental conditions for obtaining reproducible results were established. The gel was precipitated at constant pH = 10, aged at room temperature for 18 h and, after filtration, dried at 110 °C for 24 h. The phase diagram of the ZrO2/Nb2O5 system was established between 600 and 1300 °C. Phase transitions of ZrO2 and Nb2O5 were observed with XRD; and two ternary compounds, 6 ZrO2 · Nb2O5 and 12 Nb2O5 · ZrO2, were identified. The samples with a Nb2O5 content between approximately 10 and 40 mole% showed the greatest specific area and are thus best for use as catalyst supports.  相似文献   

12.
采用浸渍法制备了单一载体(Al2O3、ZrO2、CeO2)和ZrO2、CeO2改性的Al2O3复合载体的Ni催化剂,考察了在甲烷部分氧化制备合成气反应中的催化性能。通过N2-物理吸附、H2程序升温还原、X射线衍射、NH3程序升温脱附和程序升温氧化等技术对催化剂进行了表征。结果表明,在单一载体催化剂中,Ni/Al2O3具有较大的比表面积,其初始反应活性较高,但该催化剂表面易形成大量的积炭而快速失活。Ni/ZrO2和Ni/CeO2催化剂比表面积较小,活性金属Ni在其表面分散性差,催化剂具有较低的CH4转化率。而CeO2和ZrO2改性的Al2O3复合载体催化剂,具有较大的比表面积,反应活性明显高于单一载体催化剂。CeO2-Al2O3复合载体催化剂具有最高的反应活性和较好的反应稳定性。同时表明,含CeO2催化剂反应后表面积炭较少,CeO2的储放氧功能增强了催化剂对O2的活化,提高催化剂活性的同时,可以抑制积炭的生成。  相似文献   

13.
没食子酸铋锆的制备、表征及其燃烧催化作用   总被引:2,自引:0,他引:2  
以没食子酸、硝酸铋和硝酸氧锆为原料, 首次合成出了双金属有机盐——没食子酸铋锆, 采用有机元素分析、X射线荧光(XRF)光谱和傅里叶变换红外(FTIR)光谱对其进行了表征. 在程序升温条件下, 利用热重(TG)分析、差示扫描量热法(DSC)、固相原位反应池/FTIR 联用技术, 研究了没食子酸铋锆的热行为和热分解机理,描述了没食子酸铋锆的热分解过程, 分析得出其最终分解产物为Bi2O3、ZrO2和C. 利用螺压工艺制备了含没食子酸铋锆的推进剂样品, 研究了没食子酸铋锆对双基(DB)推进剂燃烧性能的影响, 分析了其燃烧催化作用. 结果表明, 没食子酸铋锆对双基推进剂的燃烧具有良好的催化作用, 是一种高效的燃烧催化剂; 没食子酸铋锆热分解的最终产物是催化燃烧的主要物质, 锆和碳则起辅助催化的作用.  相似文献   

14.
Palladium supported on γ-Al2O3 has been demonstrated as most active catalyst for catalytic combustion of methane. However, the sintering of support and PdO seriously affects its activity. We prepared a composite Pd/hexaaluminate/Al2O3 catalyst and compared its catalytic activity as well as sintering behavior with Pd/Al2O3. This composite catalyst exhibits higher activity and better resistance to sintering. The effect of water vapor presented in feed has also been investigated.  相似文献   

15.
It was found that only bridging and bidentate nitrate complexes were formed on the surface of Pt,Cu/ZrO2-pillared interlayered clay (ZrO2-PILC) upon the interaction with a flow of the (0.2% NO + 2.5% O2)/N2 mixture, whereas monodentate and nitrosyl complexes were not detected. The concentration of nitrate complexes on Pt,CU/ZrO2-PILC was higher and the strength of their bond to the surface was weaker than those on unmodified ZrO2-PILC. Isopropoxide and acetate complexes and coordinatively bound acetone were formed on the surface in the interaction of Pt,Cu/ZrO2-PILC with a flow of the (0.2% C3H6 + 2.5% O2)/N2 mixture. The supporting of Pt and Cu onto zirconium dioxide pillars resulted in considerable changes in the concentration and the temperature region of the existence of hydrocarbon surface compounds, as compared with ZrO2-PILC. Under reaction conditions at relatively low temperatures, isopropoxide and nitrate intermediates on the surface of Pt,Cu/ZrO2-PILC formed a complex structurally similar to adsorbed dinitropropane. At elevated temperatures, a surface nitromethane complex was formed in the interaction of the acetate complex with nitrate species. The spectrokinetic measurements demonstrated that the apparent rate constants of consumption of nitrate and nitroorganic complexes considerably increased on going from ZrO2-PILC to Pt,Cu/ZrO2-PILC. Moreover, the constants of consumption of nitroorganic and nitrate complexes were similar for both of the catalysts. This fact suggests that, on the test catalysts, nitroorganic complexes were reaction intermediates in the selective catalytic reduction of NOx (NOx SCR) with hydrocarbons. The found differences in the activation species and thermal stabilities of reactants can explain different activities of ZrO2-PILC and Pt,Cu/ZrO2-PILC in the SCR reaction of NOx with propylene in an excess of oxygen.  相似文献   

16.
Strategies for countering the solubility of LiMn2O4 (spinel) electrodes at 50 °C and for suppressing the reactivity of layered LiMO2 (M=Co, Ni, Mn, Li) electrodes at high potentials are discussed. Surface treatment of LiMn2O4 with colloidal zirconia (ZrO2) dramatically improves the cycling stability of the spinel electrode at 50 °C in Li/LiMn2O4 cells. ZrO2-coated LiMn0.5Ni0.5O2 electrodes provide a superior capacity and cycling stability to uncoated electrodes when charged to a high potential (4.6 V vs Li0). The use of Li2ZrO3, which is structurally more compatible with spinel and layered electrodes than ZrO2 and which can act as a Li+-ion conductor, has been evaluated in composite 0.03Li2ZrO3 · 0.97LiMn0.5Ni0.5O2 electrodes; glassy LixZrO2 + x/2 (0<x⩽2) products can be produced from colloidal ZrO2 for surface coatings.  相似文献   

17.
We studied on the function of the metal in the sulfated zirconia(SO42–/ZrO2) catalyst for the isomerization reaction of light paraffins. The addition of Pt to the SO42–/ZrO2 carrier could keep the high catalytic activity. The improvement in this isomerization activity is because Pt promotes removal of the coke precursor deposited on the catalyst surface. Though this catalytic function was observed in other transition metals, such as Pd, Ru, Ni, Rh and W, Pt exhibited the highest effect among them. It was further found that the Pd/SO42–/ZrO2–Al2O3 catalyst possessed a catalytic function for desulfurization of sulfur-containing light naphtha in addition to the skeletal isomerization. The sulfur tolerance of catalyst depended on the method of adding Pd, and the catalyst prepared by impregnation of the SO42–/ZrO2–Al2O3 with an aqueous solution of Pd exhibited the highest sulfur tolerance.Further, we investigated the improvement in sulfur tolerance of the Pt/SO42–/ZrO2–Al2O3 catalyst by impregnation of Pd. The results of EPMA analysis indicated that this catalyst was a hybrid-type one (Pt/SO42–/ZrO2–Pd/Al2O3) in which Pt/SO42–/ZrO2 particles and Pd/Al2O3 particles adjoined closely. This hybrid catalyst possessed a very high sulfur tolerance to the raw light naphtha that was obtained from the atmospheric distillation apparatus, although this light naphtha contained much sulfur. We assume that such a high sulfur tolerance in the hybrid catalyst is brought about by the isomerization function of Pt/SO42–/ZrO2 particles and the hydrodesulfurization function of Pd/Al2O3 particles. Besides, since the hybrid catalyst also provides high catalytic activity in the isomerization of HDS light naphtha, we suggest that the Pd/Al2O3 particles supply atomic hydrogen to the Pt/SO42–/ZrO2 particles by homolytic dissociation of gaseous hydrogen and also enhance the sulfur tolerance of Pt/SO42–/ZrO2 particles. Finally, we also propose the most suitable location of Pd and Pt in the metal-supported SO42–/ZrO2–Al2O3 catalyst.  相似文献   

18.
Nd_2Zr_2O_7–ZrO_2 nanocomposites were prepared via a facile process with propylene glycol as novel connecting agent and benzene tricarboxylic acid as a new complexing agent. The as-obtained Nd_2Zr_2O_7–ZrO_2 nanocomposites were characterized by transmission electron microscopy(TEM), UV–vis diffuse reflectance spectroscopy, energy dispersive X-ray microanalysis(EDX), Fourier transform infrared(FT-IR)spectroscopy, field emission scanning electron microscopy(FESEM), and X-ray diffraction(XRD). According to the morphological studies of the as-synthesized nanocomposites, it was found that the shape and particle size of Nd_2Zr_2O_7–ZrO_2 nanocomposites depended on the space-filling template type, dosage of space-filling template and tricarboxylic acid as complexing agent. Nd_2Zr_2O_7–ZrO_2 nanocomposites with different shapes and grain sizes have been synthesized. The photocatalytic behavior of as-produced Nd_2Zr_2O_7–ZrO_2 nanocomposites was also investigated through photodegradation of methylene blue dye and 2-naphthol as water pollutants.  相似文献   

19.
Ni catalysts were tested in the catalytic pyrolysis of biomass. The influence of Ni loading and various catalytic supports (ZrO2, Al2O3, ZrO2 + Al2O3, CeO2, SiO2) was studied. Although the gas phase was the main object of this study, solid and liquid residues were tested as well (mainly by TOC and GC-MS methods). Activity tests were performed in a batch reactor with mechanical stirring, equipped with on-line GC. Reaction was conducted at 700°C, with ??-cellulose as a biomass model and with waste paper as an example of raw lignocellulosic material. Reactions in the presence of a catalyst gave a higher hydrogen yield. The most promising results were obtained with Ni/ZrO2.  相似文献   

20.
Sulfur‐resistant methanation of syngas was studied over MoO3–ZrO2 catalysts at 400°C. The MoO3–ZrO2 solid‐solution catalysts were prepared using the solution combustion method by varying MoO3 content and temperature. The 15MoO3–ZrO2 catalyst achieved the highest methanation performance with CO conversion up to 80% at 400°C. The structure of ZrO2 and dispersed MoO3 species was characterized using X‐ray diffraction and transmission electron microscopy. The energy‐dispersive spectrum of the 15MoO3–ZrO2 catalyst showed that the solution combustion method gave well‐dispersed MoO3 particles on the surface of ZrO2. The structure of the catalysts depends on the Mo surface density. It was observed that in the 15MoO3–ZrO2 catalyst the Mo surface density of 4.2 Mo atoms nm?2 approaches the theoretical monolayer capacity of 5 Mo atoms nm?2. The addition of a small amount of MoO3 to ZrO2 led to higher tetragonal content of ZrO2 along with a reduction of particle size. This leads to an efficient catalyst for the low‐temperature CO methanation process.  相似文献   

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