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1.
Surface nickel (NiO
x
) species, surface NiAl
x
O
y
compound, and NiO crystallites are present on the Ni/Al 2O 3 catalysts, and the ratio of these nickel species is dependent on the nickel loading. Surface nickel interacts with the TiO 2 support to form a surface nickel titanate compound (NiTiO
x
) which has a lower reducibility. The weak interaction between the surface nickel and the silica support results in the formation of NiO crystallites on the SiO 2 surface. The Ni/Al 2O 3 and Ni/TiO 2 catalysts contain new surface Lewis acid sites and the amount of surface Lewis acid sites increases with increasing nickel concentration. The Ni/SiO 2 catalysts have no sign of the presence of the surface Lewis acid sites. Only the Ni/Al 2O 3 catalysts have shown the ammonia adsorption at temperature of 200°C. Supported nickel on alumina catalysts possess the highest amination conversion, and the amine yield increases with increasing nickel loading up to 15% and starts to level off. By comparing amination catalysis with quantitatively TPR studies of the H 2 consumed of the Ni/Al 2O 3 catalysts, it appears that the dispersed nickel species are the active sites for amination. In addition, the amination product is mainly the secondary amine due to the presence of water. 相似文献
2.
A series of solid-acid catalysts comprised of γ-alumina and modified γ-alumina with different of silica were prepared by co-precipitation method. The catalysts were characterized using XRD, TGA, NH 3-TPD and BET techniques. Dehydration of methanol to dimethyl ether (DME) on solid-acid catalysts was studied in a fixed-bed reactor at the same operating conditions ( T = 300 °C, P = 16 bar, WHSV = 26.07 h − 1). According to the experimental results, silica-modified catalysts have shown better performance compared to the pure γ-alumina. It was found that surface areas increase with increasing silica loading. The results of NH 3-TPD analysis showed that the surface acidity of aluminosilicate catalysts increases with increase in SiO 2/Al 2O 3 molar ratio. Also, it was found that the catalysts with highest portion of weak and/or moderate acid sites exhibit the best catalytic performance and stability. The sample with 3 wt.% silica loading has exhibited the best activity for methanol conversion. 相似文献
3.
We investigated the influence of the calcination temperature on the structural properties of Al 2O 3 and how the resultant Al 2O 3 support affects the characteristics of Pd/Al 2O 3 catalysts. Al 2O 3 pretreated at different calcination temperatures ranging from 500 °C to 1,150 °C, was used as catalyst supports. The Pd/Al 2O 3 catalysts were prepared by a deposition-precipitation method using a pH 7.5 precursor solution. Characterization of the prepared Pd/Al 2O 3 catalysts was performed by X-ray diffraction (XRD), N 2-physisorption, CO 2-temperature programmed desorption (TPD), CO-chemisorption, and field emission-transmission electron microscopic (FE-TEM) analyses. The CO-chemisorption results showed that the Pd catalyst with the Al 2O 3 support calcined at 900 °C, Pd/Al 2O 3 (900), had the highest and most uniformly dispersed Pd particles, with a Pd dispersion of 29.8%. The results suggest that the particle size and distribution of Pd are related to the phase transition of Al 2O 3 and the ratio of isolated tetrahedral to condensed octahedral coordination sites (i.e., functional groups), where the tetrahedral sites coordinate more favorably with Pd. 相似文献
4.
Hydrotreatment catalysts (Co–Mo/Al 2O 3, Ni–Mo/Al 2O 3 and Ni–W/Al 2O 3) were prepared by an impregnation method using an aqueous solution containing a chelating agent (nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA) or trans-1,2-cyclohexanediamine- N, N, N′, N′-tetraacetic acid (CyDTA)). Co–Mo/Al 2O 3 and Ni–W/Al 2O 3 prepared with the chelating agents showed higher hydrodesulfurization (HDS) activity as well as hydrogenation (HYD) activity under high pressure (5.1 MPa) than those prepared without the chelating agents. Co–Mo/Al 2O 3 prepared with CyDTA showed ca. 70% higher HDS activity for benzothiophene (BT) than that prepared without it. HYD activity of Ni–W/Al 2O 3 for o-xylene was promoted about 65% by the addition of CyDTA. FT-IR of nitric oxide (NO) adsorbed on the sulfided Co–Mo/Al 2O 3's suggested that Co was highly dispersed over the catalyst surface when the catalysts were prepared with the chelating agents. 相似文献
5.
Poly(trimethylene terephthalate) (PTT) is an excellent fiber materials. Although it was synthesized as early as 1940s, obtaining high‐molecular weight PTT suitable for spinning is not easy due to no evident breakthrough in the catalysts for PTT synthesis. Patents and literatures disclosed a lot of the catalysts of preparing PTT, but which are more or less disadvantageous. Based on acid catalytic mechanism of PTT preparation, a series of solid acid as x% MoO 3/(50% Al 2O 3 ? 50% TiO 2) (briefly written as xM/(A ? T), x = 0, 10, 15, 20 by weight) were prepared by sol–gel coprecipitation and wetting impregnation methods, and first used for PTT synthesis in this work. When 50% Al 2O 3 ? 50% TiO 2 (briefly written as A ? T) was supported by MoO 3 using wetting impregnation technique of (NH 4) 6Mo 7O 24.4H 2O aqueous solution, a lot of Brφnsted acid and Lewis acid sites were formed on xM/(A ? T) catalyst surfaces, which was confirmed by the characteristics of their NH 3‐TPD (temperature programmed desorption). All the prepared catalysts were highly active ones toward synthesis of PTT. PTT with high‐intrinsic viscosity (IV) was obtained in the presence of trace amount of the catalysts. IV ranging of the PTT synthesized from 0.66 to 0.95 dL g ?1 corresponds to weight average molecular weight from 49,197 to 73,004. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献
6.
The role of the Al 2O 3 support on the activity of supported Ag catalyst towards the selective catalytic reduction (SCR) of NO with decane is elucidated.
A series of Ag/Al 2O 3 catalysts were prepared by impregnation method and characterized by N 2 pore size distribution, XRD, UV–Vis, in-situ FT-IR and acidity measurement by NH 3 and pyridine adsorption. The catalytic activity differences of Ag/Al 2O 3 are correlated with different properties of Al 2O 3 supports and the active Ag species formed. 4wt% Ag supported on sol-gel prepared Al 2O 3 (Ag/Al 2O 3 (SG), showed higher NO
x
conversion (65% at 400 °C), compared with the respective catalysts made from commercial Al 2O 3 (Ag/Al 2O 3 (GB), Ag/Al 2O 3 (ALO), (∼26 and 7% at 400 °C). The higher surface area, acidity and pore size distribution in sol–gel prepared Al 2O 3 (SG) results in higher NO and hydrocarbon conversion. Based on the UV–vis characterization, the activity of NO reduction
is correlated to the presence of Ag nδ+ clusters and acidity of Al 2O 3 support was found to be one of the important parameter in promoting the formation and stabilization of Ag nδ+ clusters. Furthermore from pyridine adsorption results, presence of more number of Bronsted acid sites in Ag/Al 2O 3 (SG) is confirmed, which could also contribute to low temperature hydrocarbon activation and improve NO conversion. In situ FT-IR measurements revealed the higher rate of –CN and –NCO intermediate species formation over 4wt% Ag/Al 2O 3 (SG). We conclude that the physico–chemical properties of Al 2O 3 play a crucial role in NO
x
conversion over Ag/Al 2O 3 catalysts. Thus, the activity of the Ag/Al 2O 3 catalyst can be tailored by using a proper type of Al 2O 3 support. 相似文献
7.
This work is aimed at evaluating the performance of several catalysts in the partial hydrogenation of sunflower oil. The catalysts are composed of noble (Pd and Pt) and base metals (Ni, Co and Cu), supported on both silica and alumina. The following order can be proposed for the effect of the metal on the hydrogenation activity: Pd > Pt > Ni > Co > Cu. At a target iodine value of 70 (a typical value for oleomargarine), the production of trans isomers is minimum for supported nickel catalysts (25.7–32.4 %, depending on the operating conditions). Regarding the effect of the support, Al 2O 3 allows for more active catalysts based on noble metals (Pd and Pt) and Co, the effect being much more pronounced for Pt. Binary mixtures of catalysts have been studied, in order to strike a balance between catalyst activity and product distribution. The results evidence that Pd/Al 2O 3–Co/SiO 2 mixture has a good balance between activity and selectivity, and leads to a very low production of trans isomers (11.8 %) and a moderate amount of saturated stearic acid (13.5 %). Consequently, the utilization of cobalt‐based catalysts (or the addition of cobalt to other metallic catalysts) could be considered a promising alternative for the hydrogenation of edible oil. 相似文献
8.
The amount of basic sites of A1PO 4-Al 2O 3 (APA1-A, 5–15 wt% Al 2O 3) catalysts at two basic strengths was measured by studying the liquid-phase adsorption of two acidic molecules (benzoic acid (BA, p K = 4.2) and phenol (PH, p Ka = 9.9) from cyclohexane solutions, through the application of a spectrophotometric method. The data obtained follow the Langmuir adsorption isotherm and the monolayer coverage at equilibrium (at 298 K), X
m, is assumed as the amount of basic sites corresponding to the specific p K of the acid used as titrant. The amount of basic sites of any AlPO 4-Al 2O 3 catalyst is higher than that of AlPO 4, but lower than that of Al 2O 3. Besides, an increase in the Al 2O 3 content from 10 wt% gradually increases the basicity of the APA1-A catalyst. Moreover, calcination at increasing temperatures does not practically affect the surface basicity of APAl-A-5 and APAl-A-10 catalysts. However, for AlPO 4 content higher than 10 wt% we observe a decrease in surface basicity, this decrease depends on alumina content, i.e. it is higher as the amount of alumina increases. The basic sites of APAl-A systems catalyze the Knoevenagel condensation of p-methoxybenzaldehyde and malononitrile at room temperature and in the absence of solvent. 相似文献
9.
A novel gel-network-coprecipitation process has been developed to prepare ultrafine Cu/ZnO/Al 2O 3 catalysts for methanol synthesis from CO 2 hydrogenation. It is demonstrated that the gel-network-coprecipitation method can allow the preparation of the ultrafine Cu/ZnO/Al 2O 3 catalysts by homogeneous coprecipitation of the metal nitrate salts in the gel network formed by gelatin solution, which makes the metallic copper in the reduced catalyst exist in much smaller crystallite size and exhibit a much higher metallic copper-specific surface area. The effect of the gel concentration of gelatin on the structure, morphology and catalytic properties of the Cu/ZnO/Al 2O 3 catalysts for methanol synthesis from hydrogenation of carbon dioxide was investigated. The Cu/ZnO/Al 2O 3 catalysts prepared by the gel-network-coprecipitation method exhibit a high catalytic activity and selectivity in CO 2 hydrogenation to methanol. 相似文献
10.
Transient experiments were performed to study sulfur deactivation and regeneration of Pt/BaO/Al 2O 3 and Pt/SrO/Al 2O 3 NO
x
storage catalysts. It was found that the strontium-based catalysts are more easily regenerated than the barium-based catalysts
and that a higher fraction of the NO
x
storage sites are regenerated when H 2 is used in combination with CO 2 compared to H 2 only. 相似文献
11.
Ag/Al 2O 3 catalysts with 1 wt% SiO 2 or TiO 2 doping in alumina support have been prepared by wet impregnation method and tested for sulphur tolerance during the selective catalytic reduction (SCR) of NO x using propene under lean conditions. Ag/Al 2O 3 showed 44% NO x conversion at 623 K, which was drastically reduced to 21% when exposed to 20 ppm SO 2. When Al 2O 3 support in Ag/Al 2O 3 was doped with 1 wt% SiO 2 or TiO 2 the NO x conversion remained constant in presence of SO 2 showing the improved sulphur tolerance of these catalysts. Subsequent water addition does not induce significant deactivation. On the contrary, a slight promotional effect on the activity of NO conversion to nitrogen is observed after Si and Ti incorporation. FTIR study showed the sulphation of silver and aluminum sites of Ag/Al 2O 3 catalysts resulting in the decrease in the formation of reactive intermediate species such as –NCO, which in turn decreases NO x conversion to N 2. In the case of Ag/Al 2O 3 doped with SiO 2 or TiO 2, formation of silver sulphate and aluminum sulphate was drastically reduced, which was evident in FTIR resulting in remarkable improvement in the sulphur tolerance of Ag/Al 2O 3 catalyst. These catalysts before and after the reaction have been characterized with various techniques (XRD, BET surface area, transmittance FTIR and pyridine adsorption) for physico-chemical properties. 相似文献
12.
An investigation was conducted of noble metal and metal oxide catalysts deposited on Al2O3. The noble metals Pt, Pd, Rh the metal oxides CuO, SnO2, CoO, Ag2O, In2O3, catalysts were examined. Also investigated were noble metal Pt, Pd, Rh-doped In2O3/Al2O3 catalysts prepared by single sol–gel method. Both were studied for their capability to reduce NO by propene under lean conditions. In order to improve the catalytic activity and the temperature window, the intermediate addition propene between a Pt/Al2O3 oxidation and metal oxide combined catalyst system was also studied. Pt/Al2O3 and In2O3/Al2O3 combined catalyst showed high NO reduction activity in a wider temperature window, and more than 60% NO conversion was observed in the temperature range of 300–550 °C. 相似文献
13.
The solid base catalysts of MgO covered with SiO 2, Al 2O 3, TiO 2, and ZrO 2 were prepared by decomposition of the corresponding alkoxide over an Mg(OH) 2 surface in ethyl acetate solution followed by thermal decomposition. The acid-base properties of the prepared catalysts were estimated using 2-propanol decomposition activity and selectivity. The stability of catalysts for the aldol reaction of acetone against H 2O was examined. The acid sites were generated on the MgO surface by covering with metal oxides. Base sites were formed when the MgO was covered with Al 2O 3. Catalysts made of MgO covered with more than 7 mol% Al 2O 3 showed sufficient stability against H 2O as well as reusability. 相似文献
14.
Effect of additives, Ce and Mn, on the catalytic performance of Sn/Al 2O 3 catalyst prepared by sol–gel method for the selective reduction of NO x with propene under lean conditions was studied. Sn–Ce/Al 2O 3 catalysts exhibited higher activity than Sn/Al 2O 3 catalyst and the optimum Ce loading is 0.5–1%. The promoting effect of Ce is to enhance the oxidation of NO to NO 2 and facilitate the activation of propene, both of which are important steps for the NO x reduction. The presence of oxygen contributes to the oxidation of NO and shows a promoting effect. 相似文献
15.
An investigation was conducted of noble metal and metal oxide catalysts deposited on Al 2O 3. The noble metals Pt, Pd, Rh the metal oxides CuO, SnO 2, CoO, Ag 2O, In 2O 3, catalysts were examined. Also investigated were noble metal Pt, Pd, Rh-doped In 2O 3/Al 2O 3 catalysts prepared by single sol–gel method. Both were studied for their capability to reduce NO by propene under lean conditions. In order to improve the catalytic activity and the temperature window, the intermediate addition propene between a Pt/Al 2O 3 oxidation and metal oxide combined catalyst system was also studied. Pt/Al 2O 3 and In 2O 3/Al 2O 3 combined catalyst showed high NO reduction activity in a wider temperature window, and more than 60% NO conversion was observed in the temperature range of 300–550 °C. 相似文献
16.
Autothermal reforming (ATR) of methane was carried out over nanocrystalline Al 2O 3‐supported Ni catalysts with various Ni loadings. Mesoporous nanocrystalline γ‐Al 2O 3 powder with high specific surface area was prepared by the sol‐gel method and employed as support for the nickel catalysts. The prepared samples were characterized by X‐ray diffraction, Brunauer‐Emmett‐Teller, temperature‐programmed reduction, temperature‐programmed hydrogenation, and scanning electron microscopy techniques. It is demonstrated that the methane conversion increased with increasing in Ni content and that the catalyst with 25 wt % Ni exhibited the highest activity and a stable catalytic performance in the ATR process, with a low degree of carbon formation. Furthermore, the effects of the reaction temperature, the calcination temperature, the steam/CH 4 and O 2/CH 4 ratios, and the gas hourly space velocity on the catalytic performance of the 25 % Ni/Al 2O 3 catalyst were investigated. 相似文献
17.
A series of Al 2O 3–ZrO 2 composite supported NiMo catalysts with various ZrO 2 contents were prepared. Several techniques including XRD, SEM, N 2 physisorption, H 2-TPR, and UV–vis DRS were used for typical physico-chemical properties characterization of the ZrO 2–Al 2O 3 composite supports and their NiMo/ZrO 2–Al 2O 3 catalysts. The test results showed that the composite supports prepared by the chemical precipitation method existed as amorphous phase in the samples with insufficient contents of ZrO 2, and the incorporation of ZrO 2 into supports provided a better dispersion of NiMo species, which made their reductions become easier. The pyridine-adsorbed FT-IR results indicated that the Lewis acid sites of catalysts increased significantly by the introduction of ZrO 2 into the supports. The activities of these catalysts for diesel oil hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) were evaluated in a high pressure micro-reactor system. The results showed that the ZrO 2–Al 2O 3-supported NiMo catalysts with suitable ZrO 2 contents exhibited much higher catalytic activities than that of Al 2O 3-supported one, and when the ZrO 2 contents were 15% and 5%, the NiMo/Al 2O 3–ZrO 2 catalysts presented the highest HDS and HDN activities, respectively. 相似文献
18.
A novel catalyst Ir–FeO
x
/Al 2O 3 designed for the preferential oxidation (PROX) of CO under excess hydrogen was developed in this work. To clarify the promoting
role of Fe species, three different impregnation sequences were employed, and the resultant catalysts were characterized by
various techniques. The results showed that the Ir–FeO
x
/Al 2O 3 catalyst, which was prepared by the co-impregnation procedure, exhibited the best performance for the PROX. The partially
exposed and highly dispersed Ir sites and the FeO
x
sites allowed good adsorption for both CO and O 2 over the Ir–FeO
x
/Al 2O 3, which was believed to be responsible for the enhanced activity. 相似文献
19.
The effect of coexisting SO 2 on the catalytic activity of Ga 2O 3–Al 2O 3 prepared by impregnation, coprecipitation and sol–gel method for NO reduction by propene in the presence of oxygen was studied. Although the activity of Al 2O 3 and Ga 2O 3–Al 2O 3 prepared by impregnation (Ga 2O 3/Al 2O 3(I)) and coprecipitation (Ga 2O 3–Al 2O 3(CP)) was depressed considerably by the presence of SO 2, NO conversion on Ga 2O 3–Al 2O 3 prepared by sol–gel method (Ga 2O 3–Al 2O 3(S)) was not decreased but increased slightly by SO 2 at temperatures below 723 K. From catalyst characterization, SO 2 treatment was found to cause two important effects on the surface properties: one is the creation of Brønsted acid sites on which propene activation is promoted (positive effect), and the other is the poisoning of NO x adsorption sites on which NO reduction proceeds (negative effect). It was presumed that the influence of SO 2 treatment on the catalytic activity is strongly related to the balance between the negative and positive. The activity enhancement of Ga 2O 3–Al 2O 3(S) by SO 2 was accounted for by the following consideration: (1) increase of the propene activation ability by SO 2, (2) incomplete inhibition of NO x adsorption sites by SO 2. 相似文献
20.
The promotional effect of Ni on the hydrodeoxygenation (HDO) of benzofuran (BF) over reduced Ni–Mo/γ-Al 2O 3 catalysts was studied. The adsorption characteristics of Al 2O 3 support, mono-metallic Mo, and bi-metallic Ni–Mo catalysts that were pre-reduced were investigated using the feed molecule (BF) and a probe molecule (NO) as adsorbates. NO was used to probe the coordinatively unsaturated sites (CUS). Three adsorption modes for benzofuran over reduced Al 2O 3 support, Mo, and Ni–Mo catalysts were proposed that involved OH groups, Brønsted acid sites, and CUS, respectively. Benzofuran molecule adsorbed more strongly on B acid sites and CUS than on OH groups and was activated with weakening of the C–O bond. With increasing catalytic hydrogenation activity (increasing CUS) and/or decreasing hydrogenolysis activity (decreasing acidity), the reaction pathway for benzofuran HDO changes from a hydrogenolysis route to a route that involves saturation of the benzene ring before any heteroatom removal takes place. 相似文献
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