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1.
Millimeter size γ‐Al2O3 beads were prepared by alginate assisted sol–gel method and grafting organic groups with propyl sulfonic acid and alkyl groups as functionalized γ‐Al2O3 bead catalysts for fructose dehydration to 5‐hydroxymethylfurfural (5‐HMF). Experiment results showed that the porous structure of γ‐Al2O3 beads was favorable to the loading and dispersion of active components, and had an obvious effect on the properties of the catalyst. The lower calcination temperature of γ‐Al2O3 beads increased the specific surface area, the hydrophobicity and the activity of catalysts. Competition between the reaction of alkyl groups and ‐SH groups with surface hydroxyl during the preparation process of the catalyst influenced greatly the acid site densities, hydrophobic properties and activity of the catalyst. With an increase in the alkyl group chain, the hydrophobicity of catalysts increased obviously and the activity of the catalyst was enhanced. The most hydrophobic catalyst C16‐SO3H‐γ‐Al2O3–650°C exhibited the highest yield of 5‐HMF (84%) under the following reaction conditions: reaction medium of dimethylsulfoxide/H2O (V/V, 4:1), catalyst amount of 30 mg, temperature of 110°C and reaction time of 4 hr.  相似文献   

2.
Pt‐Co/Al2O2 catalyst has been studied for CO2 reforming of CH4 to synthesis gas. It was found that the catalytic performance of me catalyst was sensitive to calcination temperature. When Co/Al2O3 was calcined at 1473 K prior to adding a small amount of Pt to it, the resulting bimetallic catalyst showed high activity, optimal stability and excellent resistance to carbon deposition, which was more effective to the reaction than Co/Al2O3 and Pt/Al2O3 catalysts. At lower metal loading, catalyst activity decreased in the following order: Pt‐Co/ Al2O3 > Pt/Al2O3 > Co/Al2O3. With 9% Co, the Co/Al2O3 calcined at 923 K was also active for CO2 reforming of CH4, however, its carbon formation was much more fast man that of the Pt‐Co/Al2O3 catalyst. The XRD results indicated that Pt species well dispersed over the bimetallic catalyst. Its high dispersion was related to the presence of CoAl2O4, formed during calcining of Co/Al2O3 at high temperature before Pt addition. Promoted by Pt, Co/Al2O4 in the catalyst could be reduced partially even at 923 K, the temperature of pre‐reduction for the reaction, confirmed by TPR. Based on these results, it was considered that the zerovalent platinum with high dispersion over the catalyst surface and the zerovalent cobalt resulting from Co/Al2O4 reduction are responsible for high activity of the Pt‐Co/Al2O3 catalyst, and the remain Co/Al2O4 is beneficial to suppression of carbon deposition over the catalyst.  相似文献   

3.
Supported vanadium oxides are one of the most promising alternative catalysts for propane dehydrogenation (PDH) and efforts have been made to improve its catalytic performance. However, unlike Pt‐based catalysts, the nature of the active site and surface structure of the supported vanadium catalysts under reductive reaction conditions still remain elusive. This paper describes the surface structure and the important role of surface‐bound hydroxyl groups on VOx / γ‐Al2O3 catalysts under reaction conditions employing in situ DRIFTS experiments and DFT calculations. It is shown that hydroxyl groups on the VOx /Al2O3 catalyst (V?OH) are produced under H2 pre‐reduction, and the catalytic performance for PDH is closely connected to the concentration of V?OH species on the catalyst. The hydroxyl groups are found to improve the catalyst that leads to better stability by suppressing the coke deposition.  相似文献   

4.
The effect of manganese on the dispersion, reduction behavior and active states of surface of supported copper oxide catalysts have been investigated by XRD, temperature‐programmed reduction and XPS. The activity of methanol synthesis from CO2/H2 was also investigated. The catalytic activity over CuO‐MnOx/γ‐Al2O3 catalyst for CO2 hydrogenation is higher than that of CuO/γ‐Al2O3. The adding of manganese is beneficial in enhancing the dispersion of the supported copper oxide and make the TPR peak of the CuO‐MnKx/γ‐Al2O3 catalyst different from the individual supported copper and manganese oxide catalysts, which indicates that there exists strong interaction between the copper and manganese oxide. For the CuO/γ‐Al2O3 catalyst there are two reducible copper oxide species; α and β peaks are attributed to the reduction of highly dispersed copper oxide species and bulk CuO species, respectively. For the CuO‐MnOx/γ‐Al2O3 catalyst, four reduction peaks are observed, α peak is attributed to the dispersed copper oxide species; β peak is ascribed to the bulk CuO; γ peak is attributed to the reduction of high dispersed CuO interacting with manganese; δ peak may be the reduction of the manganese oxide interacting with copper oxide. XPS results show that Cu+ mostly existed on the working surface of the Cu‐Mn/γ‐Al2O3 catalysts. The activity was promoted by Cu with positive charge which was formed by means of long path exchange function between Cu? O? Mn. These results indicate that there is synergistic interaction between the copper and manganese oxide, which is responsible for the high activity of CO2 hydrogenation.  相似文献   

5.
It was studied the influence of gold addition on physico-chemical properties and catalytic activity of bimetallic Ni-Au/Al2O3 catalyst in partial oxidation of methane (POM). The reduction behavior in hydrogen, XRD crystal structure, XPS spectra and POM catalytic activity were investigated. The reduction of Ni-Au catalyst is a prerequisite condition to catalyze POM reaction. The formation of Ni-Au alloy during high temperature reduction in hydrogen and also in the conditions of POM reaction was experimentally proved. The addition of gold to Ni/Al2O3 system improves catalyst stability and activity in POM reaction.  相似文献   

6.
Three‐dimensional flower‐like α‐Fe2O3 nanostructures have been successfully synthesized by a simple surfactant‐free environmental friendly solvolthermal process. The as‐prepared products were investigated by X‐ray powder diffraction, transmission electron microscopy, and field emission scanning electron microscopy. By adjusting the synthetic parameters, the shape of the α‐Fe2O3 nanostructures can be controlled. The three‐dimensional flower‐like α‐Fe2O3 nanostructures were found to be highly active as catalysts for phenol alkylation. The effects of various parameters, such as reaction temperature, reaction time and the amount of catalyst, were studied. The catalyst was stable and could be reused three times in normal atmosphere without suffering appreciable loss in catalytic activity. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

7.
The Beckmann rearrangement of cyclohexanone oxime (CHO) to ?‐caprolactam (?‐C) was studied in a plug flow reactor at 300–400°C under atmospheric pressure by using Hβ, ZSM‐5, and alumina pillared montmorillonite. With Hβ(X) Y zeolites, raising the SiO2/Al2O3 molar ratio (X) results in the enhancement of catalyst acid strength with concomitant decrease of the total acid amount. In creasing the calcination temperature (Y) causes remarkable diminution of catalyst surface area, acid strength, and acid amount. A similar trend was found for AlPMY catalysts. In there action of CHO, the initial catalytic activity correlates well with the total acid amount of various catalysts except for Hβ(10) Y (Y > 600°C). The reaction proceeds on both Brönsted and Lewis acid sites and the catalyst deactivation most likely occurs at the strong Brönsted acid sites. The effect of solvents in the feed on the catalytic results was also investigated; it was found that polar solvents such as ethanol or n‐butanol give high ?‐C yield and longer catalyst life time. In the reaction of CHO/C2H5OH over Hβ(10)800 at 400°C and W/F 74.6 gh/mol, the CHO conversion and ?‐C yield remain 100% and 92%, respectively, for at least 20 h time‐on‐stream. The reaction paths and the mechanism for ?‐C formation are proposed.  相似文献   

8.
焙烧温度对 Pd/Al2O3 催化剂上甲烷燃烧反应性能的影响   总被引:1,自引:0,他引:1  
高典楠  王胜  刘莹  张纯希  王树东 《催化学报》2010,31(11):1363-1368
 考察了载体与催化剂焙烧温度对 Pd/Al2O3 催化剂上低浓度甲烷催化燃烧反应性能的影响. 采用 X 射线衍射、透射电镜、N2 物理吸附、NH3 程序升温脱附和 O2 程序升温氧化等手段对载体和催化剂进行了表征. 结果表明, 焙烧温度对催化剂活性及稳定性的影响显著. 随着载体焙烧温度的升高, Al2O3 的比表面积、物相结构、酸中心的数量及强度明显改变, 相应的 Pd/Al2O3 催化剂中载体与 Pd 的相互作用减弱, Pd 分散度降低. 当载体焙烧温度为 1 100 °C, Pd/Al2O3 焙烧温度为 200 °C 时, 所得催化剂在 260 h 的连续反应中, 甲烷转化率始终维持在 99%以上.  相似文献   

9.
Vapor‐phase aldol condensation of n‐butyraldehyde to 2‐ethyl‐2‐hexenal was studied at 1 atm and 150~ 300°C in a fixed‐bed, integral‐flow reactor by using NaX, KX, γ‐Al2O3 and Na/NaOH/γ‐Al2CO3 catalysts. Ion exchange of NaX zeolite with potassium acetate solution results in a decrease of crystallinity and apparent lowering of surface area, whereas the basic strength is enhanced. Treatment of γ‐Al2O3 with NaOH and Na causes a large decrease of the surface area but strong enhancement of the catalyst basicity. The catalytic activity on the basis of unit surface area is in the order Na/NaOH/γ‐Al2O3 < KXU < KXW < NaX >γ‐Al2O3, in accordance with the relative catalyst basic strength. The molar ratio of trimeric to dimeric products increases with increasing the reaction temperature and the catalyst basic strength except for Na/NaOH/γ‐Al2O3. Very high selectivity of 2‐ethyl‐2‐hexenal (>98.5%) was observed for reactions over NaX zeolite at 150°C. Based on the FT‐IR and the catalytic results, the reaction paths are proposed as follows: self‐aldol condensation of n‐butyraldehyde, followed by dehydration produces 2‐ethyl‐2‐hexenal, which then reacts with n‐butyraldehyde and successively dehydrates to 2,4‐diethyl‐2,4‐octadienal and 1,3,5‐triethylbenzene. For the reaction over NaX, the calculated Arrhenius frequency factor and activation energy are 314 mol/g·h and 32.6 kJ/mol, respectively.  相似文献   

10.
Liquid phase hydrogenolysis of ethyl lactate to 1,2‐propanediol was performed over silica supporting cobalt catalysts prepared by two different methods: precipitation‐gel (PG) technique and deposition‐precipitation (DP) procedure. The cobalt species (Co3O4/cobalt phyllosilicate) present in the corresponding calcined PG and DP catalysts were different as a consequence of the preparation methods, and Co OH Co olation and Si O Co oxolation molecular mechanisms were employed to elucidate the chemical phenomena during the different preparation procedures. In addition, the texture (BET), reduction behavior (TPR and in‐situ XRD), surface dispersion and state of cobalt species (XPS), and catalytic performance differ greatly between the samples. Because of small particle size, high dispersion of cobalt species and facile reducibility, the Co/SiO2 catalyst prepared by precipitation‐gel method presented a much higher activity than the catalyst prepared by deposition‐precipitation method. Metallic cobalt is assumed to be the catalytically active site for the hydrogenolysis reaction according to the catalytic results of both cobalt samples reduced at different temperatures and the structure changes after reaction.  相似文献   

11.
Water pollution by polychlorinated aromatic hydrocarbons has always been a global issue. In this work, we reported a synthesis of supported palladium catalysts Pd/C, Pd/CeO2, Pd/SBA‐15, Pd/ZrO2,Pd/SiO2, and Pd/Al2O3 as well as their catalytic activities on hydrodechlorination (HDC) of 1,2,4,5‐tetrachlorobenzene (TeCB). These Pd catalysts were characterized by Brunauer‐Emmett‐Teller (BET) specific surface area, Transmission electron microscopy (TEM), X‐ray diffraction (XRD), energy Dispersive X‐ray Fluorescence (EDXRF), CO‐chemisorption, and H2‐temperature programmed reduction (H2‐TPR) analysis. Pd/C, Pd/CeO2 and Pd/SBA‐15 catalysts showed relatively high catalytic activities. The catalytic activities were associated with dispersion of Pd, metal surface area, and reaction temperature, etc.  相似文献   

12.
The structural and chemical stabilities of immobilized polyoxometalate (POM)‐containing catalysts are crucial factors for their industrial application. An alumina supported POM catalyst is prepared by using a facile condensation reaction between the trilacunary POM Na12[α‐P2W15O56] ? 24 H2O (P2W15) and the hydroxy groups on the surface of γ‐Al2O3 spheres under acidic conditions. The heterogeneous catalyst P2W15?Al2O3 is characterized by a wide variety of techniques and shows excellent stability and highly efficient reactivity and selectivity for the oxygenation of thioethers to sulfoxides, which are a very useful intermediate in organic synthesis and the industrial preparation of drugs. Furthermore, P2W15?Al2O3 can be recycled and reused at least ten times without any observable loss of its catalytic efficiency, mainly due to the covalent immobilization and high dispersion of P2W15 on the γ‐Al2O3 surface.  相似文献   

13.
The correlation between phase structures and surface acidity of Al2O3 supports calcined at different temperatures and the catalytic performance of Ni/Al2O3 catalysts in the production of synthetic natural gas (SNG) via CO methanation was systematically investigated. A series of 10 wt% NiO/Al2O3 catalysts were prepared by the conventional impregnation method, and the phase structures and surface acidity of Al2O3 supports were adjusted by calcining the commercial γ-Al2O3 at different temperatures (600–1200 °C). CO methanation reaction was carried out in the temperature range of 300–600 °C at different weight hourly space velocities (WHSV = 30000 and 120000 mL·g?1·h?1) and pressures (0.1 and 3.0 MPa). It was found that high calcination temperature not only led to the growth in Ni particle size, but also weakened the interaction between Ni nanoparticles and Al2O3 supports due to the rapid decrease of the specific surface area and acidity of Al2O3 supports. Interestingly, Ni catalysts supported on Al2O3 calcined at 1200 °C (Ni/Al2O3-1200) exhibited the best catalytic activity for CO methanation under different reaction conditions. Lifetime reaction tests also indicated that Ni/Al2O3-1200 was the most active and stable catalyst compared with the other three catalysts, whose supports were calcined at lower temperatures (600, 800 and 1000 °C). These findings would therefore be helpful to develop Ni/Al2O3 methanation catalyst for SNG production.  相似文献   

14.
A series of Keggin‐type heteropolyacid‐based heterogeneous catalysts (Co‐/Fe‐/Cu‐POM‐octyl‐NH3‐SBA‐15) were synthesized via immobilized transition metal mono‐ substituted phosphotungstic acids (Co‐/Fe‐/Cu‐POM) on octyl‐amino‐co‐functionalized mesoporous silica SBA‐15 (octyl‐NH2‐SBA‐15). Characterization results indicated that Co‐/Fe‐/Cu‐POM units were highly dispersed in mesochannels of SBA‐15, and both types of Brønsted and Lewis acid sites existed in Co‐/Fe‐/Cu‐POM‐octyl‐NH3‐SBA‐15 catalysts. Co‐POM‐octyl‐NH3‐SBA‐15 catalyst showed excellent catalytic performance in H2O2‐mediated cyclohexene epoxidation with 83.8% of cyclohexene conversion, 92.8% of cyclohexene oxide selectivity, and 98/2 of epoxidation/allylic oxidation selectivity. The order of catalytic activity was Co‐POM‐octyl‐NH3‐SBA‐15 > Fe‐POM‐octyl‐NH3‐SBA‐15 > Cu‐POM‐octyl‐NH3‐SBA‐15. In order to obtain insights into the role of ‐octyl moieties during catalysis, an octyl‐free catalyst (Co‐POM‐NH3‐SBA‐15) was also synthesized. In comparison with Co‐POM‐NH3‐SBA‐15, Co‐POM‐octyl‐NH3‐SBA‐15 showed enhanced catalytic properties (viz. activity and selectivity) in cyclohexene epoxidation. Strong chemical bonding between ‐NH3+ anchored on the surface of SBA‐15 and heteropolyanions resulted in excellent stability of Co‐POM‐octyl‐NH3‐SBA‐15 catalyst, and it could be reused six times without considerable loss of activity.  相似文献   

15.
The oxidant‐free dehydrogenation of n‐pentanol over copper based catalysts was investigated in this paper. The effect of metal modification on the activity and stability of the copper catalyst supported on γ‐Al2O3 and La2O3 (Cu/γ‐Al2O3‐La2O3) was clarified and a Cr modified Cu/Al2O3‐La2O3 (Cu‐Cr/γ‐Al2O3‐La2O3) showed the best catalytic performance. The conversion of n‐pentanol was 70.0% and the selectivity for n‐pentanal increased to 97.1% over Cu‐Cr/γ‐Al2O3‐La2O3. X‐ray diffraction and temperature programmed reduction of H2 indicated that the addition of Cr favors the formation and reduction of the copper oxide, and the dispersion of the active Cu0 species, accounting for the good activity and stability of this catalyst. Furthermore, the lower amount of acidic sites in Cu‐Cr/γ‐Al2O3‐La2O3 is suggested to suppress the dehydration in oxidant‐free dehydrogenation of n‐pentanol, accounting for the higher selectivity for n‐pentanal.  相似文献   

16.
This work is focused on the role of gold and Al3CrO6 support for physicochemical properties, and catalytic activity of supported nickel catalysts in partial oxidation of methane (POM). Catalysts, containing 5% Ni and 5% Ni-2% Au active phases dispersed on mono- (Al2O3, Cr2O3) and bi-oxide Al3CrO6 support, were investigated by TPR, BET and XRD methods, and the activity tests in POM reaction were carried out. Bimetallic Ni-Au catalysts dispersed on Al3CrO6 support remained highly stable and active. The amorphous binary oxide Al3CrO6 can stabilize considerable amount of Cr4+, Cr5+, and Cr6+ species in Ni-Au/Al3CrO6 catalyst network during its calcination in the air. Nickel supported on binary oxide Ni/Al3CrO6 can form Ni(III)CrO3 bi-oxide phase in reductive conditions. During TPR H2 reduction of Ni-Au/Al3CrO6 catalyst chromium(II) oxide Cr(II)O phase is observed. After POM reaction the existence of bimetallic Au-Ni alloy was experimentally confirmed on mono-oxide Al2O3 support surface, but its formation was not identified on bioxide Al3CrO6 support. Published in Russian in Kinetika i Kataliz, 2009, Vol. 50, No. 1, pp. 149–156. The article is published in the original. Based on a report at the VII Russ. Conf. on Mechanisms of Catalytic Reactions (with international participation), St. Petersburg, July 2–8, 2006.  相似文献   

17.
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   

18.
Dimethyldichlorosilane, one of the most consumed organosilicon monomers in the industry, can be prepared in a highly efficient and environmentally friendly synthesis method of disproportionating methylchlorosilanes. However, the internal mechanism of the reaction remains unclear. In this paper, the mechanism catalyzed by AlCl3/MIL‐53(Al) and AlCl3/MIL‐53(Al)@γ‐Al2O3 catalysts was calculated at B3LYP/6‐311++G(3df, 2pd) level by using the density functional theory (DFT). The results showed that although the two catalysts had similar active structures, the catalytic effects were significantly different. The Lewis acid center on the surface of γ‐Al2O3 in the core‐shell catalyst is complementary to the classic Lewis acid AlCl3 through the spatial superposition effect, which greatly improves the Lewis acid catalytic activity of AlCl3/MIL‐53(Al)@γ‐Al2O3.  相似文献   

19.
Gold catalysts with loadings ranging from 0.5 to 7.0 wt% on a ZnO/Al2O3 support were prepared by the deposition–precipitation method (Au/ZnO/Al2O3) with ammonium bicarbonate as the precipitation agent and were evaluated for performance in CO oxidation. These catalysts were characterized by inductively coupled plasma-atom emission spectrometry, temperature programmed reduction, and scanning transmission electron microscopy. The catalytic activity for CO oxidation was measured using a flow reactor under atmospheric pressure. Catalytic activity was found to be strongly dependent on the reduction property of oxygen adsorbed on the gold surface, which related to gold particle size. Higher catalytic activity was found when the gold particles had an average diameter of 3–5 nm; in this range, gold catalysts were more active than the Pt/ZnO/Al2O3 catalyst in CO oxidation. Au/ZnO/Al2O3 catalyst with small amount of ZnO is more active than Au/Al2O3 catalyst due to higher dispersion of gold particles.  相似文献   

20.
This study aims to develop highly efficient, recyclable solid catalysts for the epoxidation of vegetable oils. An Al2O3–ZrO2–TiO2 solid acid catalyst was prepared by a co‐precipitation/impregnation method and characterised through scanning electron microscopy, energy‐dispersive spectroscopy, X‐ray diffraction, X‐ray photoelectron spectroscopy, Fourier‐transform infrared and nitrogen adsorption–desorption analyses. The solid acid catalyst with a high surface area and typical slit pore adsorption was successfully synthesised. Al2O3–ZrO2–TiO2 also exhibits high stability and improved catalytic efficiency in the epoxidation of soybean oil. An oil conversion rate of 86.6%, which is higher than that of conventional catalysts, was obtained with a catalyst loading of 0.8 wt% and was maintained at 76.6% even after recycling the catalyst three times. The performance of the solid catalyst was slightly superior to that of H2SO4. Therefore, this novel catalyst may potentially be applicable in catalysing soybean oil epoxidation.  相似文献   

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